ULTRASONOGRAPHY IN DENTISTRY

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ULTRASONOGRAPHY IN DENTISTRY:

ULTRASONOGRAPHY IN DENTISTRY SAJIDA SULTANA. N , C.R.R.I

Introduction:

Introduction Ultrasound is an oscillating sound pressure wave with a frequency greater than the upper limit of the human hearing range . Thus not separated from "normal" (audible) sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is approximately 20 kilohertz (20,000 hertz) in healthy, young adults. Ultrasound devices operate with frequencies from 20 kHz up to several gigahertz.

Applications:

Applications

History:

History Acoustics , the science of sound, starts as far back as Pythagoras in the 6th century BC, who wrote on the mathematical properties of stringed instruments. Sir Francis Galton constructed a whistle producing ultrasound in 1893. The first technological application of ultrasound was an attempt to detect icebergs by Paul Langevin in 1917. The piezoelectric effect discovered by Jacques and Pierre Curie in 1880 was useful in transducers to generate and detect ultrasonic waves in air and water. Echolocation in bats was discovered by Lazzaro Spallanzani in 1794, when he demonstrated that bats hunted and navigated by inaudible sound and not vision.

Imaging:

Imaging The potential for ultrasonic imaging of objects, with a 3 GHZ sound wave producing resolution comparable to an optical image, was recognized by Sokolov in 1939 but techniques of the time produced relatively low-contrast images with poor sensitivity. Ultrasonic imaging uses frequencies of 2 megahertz and higher; the shorter wavelength allows resolution of small internal details in structures and tissues. The power density is generally less than 1 watt per square centimetre , to avoid heating and cavitation effects in the object under examination. High and ultra high ultrasound waves are used in acoustic microscopy , with frequencies up to 4 gigahertz. Ultrasonic imaging applications include industrial non-destructive testing, quality control and medical uses.

Types:

Types A mode - Amplitute mode – not in use B mode – Brightness mode – Producing different echogenicity M mode Doppler Grey scale Real time Endoscopic

Pulse-Echo Scan of Human Tooth:

Pulse-Echo Scan of Human Tooth

PowerPoint Presentation:

Dentistry in the modern era is emerging with the use of advanced imaging techniques such as computed tomography(ct),magnetic resonance imaging (MRI), nuclear medicine (NM), and ultrasound (US), of which MRI and ultrasound are the only imaging technique, which operate without causing radiation hazards to the patients. It is one of the advanced imaging techniques which uses sound waves for viewing the normal and pathological conditions involving bone and soft tissue of the oral and maxillofacial region. In dentistry for detecting a bony (or) soft tissue mass, patients are exposed to multiple radiographs which might cause radiation effects at the tissue and organ level. So this valuable technique can be used prior to use of x-ray radiation.

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Sonography was introduced in the Medical field in early 1950's with steady development and requirement of Ultrasound equipment for diagnosis has improved the Medical field & now in dentistry. In diagnostic Ultrasound high frequency sound waves are transmitted in to the body by a transducer and echoes from tissue interface are detected and displayed on a screen. The transducers are designed to produce longitudinal waves hence only those waves can pass through tissues get reflected, Audiofrequency of a sound wave is 20 KHz. Anything below this is called infrasonic and above this Ultrasound. Medical Ultrasound uses the frequency of 1-15 MHz (2.5, 3.5, 7.5 and 10 MHz). The transducer has a special property called piezoelectric effect i.e. they can convert sound waves in to electrical waves and vice versa.

Packaged Single-Element Ultrasound Transducer:

Packaged Single-Element Ultrasound Transducer

Piezoelectric Transducer Array:

Piezoelectric Transducer Array

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As like x-ray, sound beam from ultrasound are waves transmitting energy, x-ray passes readily in vacuum, whereas sound requires medium for its transmission. Sound waves travel slowest in gases, at intermediate velocity in liquids and most rapidly in solids. All body tissues except bone behave like liquids and therefore, they all transmit sound at about some velocity. A velocity of 1540 m/sec is used as an average for body tissues. Ultrasonography is one method of imaging which lacks radiation hazards, this imaging technique can be used for bone and soft tissue examination, either normal (or) pathological lesions, detection of calculi in major salivary glands, tmj imaging, detection of fractures & vascular lesions. So proper application of this method can be of great importance in dentistry.

Application of US:

Application of US Ultrasonic echography has been used as an instant, non-invasive method for the observation of relatively deep areas, recently, however high frequency echography has been developed that can provide detail investigation of more superficial regions . Ultrasound in dentistry is used for detection of fractures of the maxillo facial region i.e. nasal bone Fractures, orbital rim fractures, maxillary fractures, mandibular fractures, zygomatic arch fractures and for locating the position of mandibular condyles . And post operative view can be done instantly to view the reduction & healing of fractures.

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Ultrasound can be used to detect parotid lesions, where solid and cystic lesions are reliably differentiated and diffuse enlargement of the parotid gland (or) focal disease is readily shown by ultrasound. Sonographically, benign lesions usually look well defined, homogeneous and hypo echoic, while malignant lesions tend to be ill defined and hypo echoic with heterogeneous internal architecture and enlarged cervical lymph node may be visible and reactive intra parotid lymph nodes may also be readily assessed.

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Ultra sound can also be used during FNAC (or) FNAB, central sampling of a solid lesions is more reliable than peripheral sampling. So ultra sound guidance circumvents this problem by ensuring that the lesion itself is sampled. This technique offers the ability to sample non- palpable diseases, gives access to different regions of the lesion and approaches the lesion from different angles. The use of spring – loaded device such as biopsy (or) magnum gun to discharge the needle also offers the advantage of precise and co- ordinated cutting action.

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This combined with ultrasound ensures that the needle is placed with in the lesion and does not exit the lesion and during biopsy of parotid gland there is chance of injuring the facial nerve (or) seeding neoplastic cells, under ultrasound guidance these can be avoided . The value of ultrasonography is well recognized in inflammatory soft tissue conditions of the head and neck region and superficial tissue disorders of the maxillofacial region. Ultra sound can provide the content of the lesion before any surgical procedure, both solid and cystic Contents could be identified in ultrasound. The mixed lesions should be considered neoplastic and should be biopsied before surgical procedure.

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Ultrasound with aid of high resolution transducer, can demonstrate the internal muscle structures more clearly than CT. Hyper echoic bands, which corresponds to the internal fascia are usually observed on us image of normal muscles and are sometimes referred to as septa. These bands diminish or disappear with inflammation; hence this is an important structural index of masseteric infection. Ultrasound is also an accurate modality for measuring the thickness of muscles, data regarding thickness may provide information useful in diagnosis and treatment especially in follow up examination.

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Ultrasound can also be used for detecting sialoliths in parotid, submandibular and sublingual salivary glands, which appear as echo-dense spots with a characteristic acoustic shadow . In ultrasound, color doppler sonography has been developed to identify vasculatures and to enable evaluation of the blood flow, velocity and vessel resistance together with surrounding morphology . It can be used for detecting the coarse of the facial artery and for detecting hemangioma . So the use of ultrasound is unlimited, so proper application of this imaging can be of use in detecting various normal & pathological lesion in the maxillofacial region.

SALIVARY GLANDS :

SALIVARY GLANDS

Examination:

Examination The examination should be carried out with the highest-frequency transducer possible. Usually, 5–12-MHz wide-band linear transducers (median frequency, 7–7.5 MHz or more) are used . In assessment of large tumors and lesions located in deep portions of the glands, 5–10-MHz transducers may be useful . Probes with a median frequency above 10 MHz may be useful in evaluation of the internal structure of salivary glands . Entire salivary glands and all lesions have to be evaluated in at least two perpendicular planes during a US examination. The whole neck should also be scanned to assess lymph nodes and search for concomitant or related disease.

Anatomy:

Anatomy Parotid Gland The parotid gland is located in the retromandibular fossa, anterior to the ear and sternocleidomastoid muscle. Parts of the superficial lobe cover the ramus of the mandible and the posterior part of the masseter muscle.

Transverse panoramic US image and corresponding diagram show the normal anatomy of the left parotid gland and part of the cheek muscle.:

Transverse panoramic US image and corresponding diagram show the normal anatomy of the left parotid gland and part of the cheek muscle.

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The border between the superficial and deep parotid lobes is created by a plane in which the facial nerve and its branches are located. Branches of the facial nerve are not visible at US. Parts of the trunk of this nerve may be demonstrated only with high-frequency probes (above 10 MHz) . Therefore, the retromandibular vein, which usually lies directly above the trunk of the facial nerve , is used as a US landmark separating the superficial and deep lobes of the parotid gland . Although the extracranial portion of the facial nerve may be visualized on high-resolution MR images, the retromandibular vein is commonly used as an anatomic landmark in preoperative CT and MR imaging examinations of parotid neoplasms . The deep parotid lobe can be visualized only partially at US. Some areas of glandular parenchyma and possible lesions may be hidden in the acoustic shadow behind the mandibular ramus .

Drawing shows the major blood vessels in the area of the salivary glands.:

Drawing shows the major blood vessels in the area of the salivary glands. 1 = retromandibular vein, 2 = external carotid artery, 3 = facial artery and vein, 4 = lingual artery and vein, 5 = external carotid artery, 6 = internal jugular vein, 7 = external jugular vein.2

 Transverse and longitudinal US images show the normal anatomy of the left parotid gland. The positions of the US probe are shown in the inset diagrams.:

Transverse and longitudinal US images show the normal anatomy of the left parotid gland. The positions of the US probe are shown in the inset diagrams. 1 = retromandibular vein, 2 = external carotid artery, 3 = echo from the surface of the mandible, 4 = parotid gland, 5 = masseter muscle

 Transverse US image of the right parotid gland and corresponding diagram show the border between the superficial and deep lobes of the gland. The position of the US probe is shown in the inset diagram.:

Transverse US image of the right parotid gland and corresponding diagram show the border between the superficial and deep lobes of the gland. The position of the US probe is shown in the inset diagram.

PowerPoint Presentation:

The normal echogenicity of all major salivary glands, including the parotid gland, is generally homogeneous and varies from very bright and markedly hyperechoic to only slightly hyperechoic in comparison to adjacent muscles. The echogenicity of the parotid gland depends on the amount of intraglandular fatty tissue. Salivary glands with high fat content are hyperechoic in comparison to surrounding muscles and markedly suppress ultrasound waves, so that the deep lobe is inaccessible for US assessment and sometimes even large vessels crossing the parotid gland—the retromandibular vein and external carotid artery—are barely visible or not visible at all on gray-scale images

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Transverse panoramic US image of the left parotid gland (arrows) and cheek shows that the gland has a high fat content. The parenchyma is hyperechoic with marked suppression of ultrasound waves, and no vessels are visible. The position of the US probe is shown in the inset diagram. 1 = masseter muscle.

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After leaving the parotid gland, the main excretory duct ( Stenon duct) lies on the masseter muscle, about 1 cm below the zygomatic arch, then crosses the buccal muscle and has its orifice in the parotid papilla at the level of the upper second molar. The length of the Stenon duct usually varies between 3 and 5 cm. A nondilated duct is usually not visible during US examination . However, some authors report showing intraglandular nondilated parts of the Stenon duct with high-resolution US

Diagram shows the location of the Stenon duct. Panoramic US image shows a dilated Stenon duct in a patient with sialolithiasis and inflammation.:

Diagram shows the location of the Stenon duct. Panoramic US image shows a dilated Stenon duct in a patient with sialolithiasis and inflammation. 1 = parotid gland, 2 = Stenon duct, 4 = masseter muscle, 5 = surface of the mandible, 6 = buccal muscle, large arrow = retromandibular vein and external carotid artery.

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Along the course of the Stenon duct in the soft tissues of the cheek, an accessory parotid gland may be found, unilaterally or bilaterally. The accessory parotid gland may also be the site of salivary gland tumors, benign or malignant.

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In the parenchyma of the parotid gland, lymph nodes may be found. They are localized mainly in the area of the upper and lower poles of the gland. Normal intraparotid lymph nodes may be oval or have a longitudinal shape . Almost 60% of parotid nodes have a short axis–to–long axis ratio greater than 0.5. The presence of a hyperechoic hilum is one of the important criteria for the normality of parotid lymph nodes. Their short axis should not exceed 5–6 mm in the normal state . With the application of sensitive power Doppler US, central vessels may be seen in normal parotid lymph nodes.

Submandibular Gland:

Submandibular Gland The submandibular gland lies in the posterior part of the submandibular triangle. The sides of the submandibular triangle are created by the anterior and posterior bellies of the digastric muscle and the body of the mandible. The space anterior to the submandibular gland is occupied by connective tissue and lymph nodes. Generally, the shape of the submandibular gland in longitudinal and transverse sections is close to a triangle . The submandibular gland may be connected with the parotid or sublingual gland by the glandular processes.

US image obtained obliquely relative to the mandible (a) and corresponding diagram (b)show the left submandibular gland with surrounding structures. :

US image obtained obliquely relative to the mandible (a) and corresponding diagram (b) show the left submandibular gland with surrounding structures.

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The facial artery may cross the parenchyma of the submandibular gland in its tortuous course. The facial vein runs along the anterosuperior part of the submandibular gland. In its posterior portion, a branch connecting with the retromandibular vein may be found. Medially to the submandibular gland run the lingual artery and vein.

US image shows the tortuous facial artery (arrowheads) crossing the parenchyma of the right submandibular gland (arrows).:

US image shows the tortuous facial artery (arrowheads) crossing the parenchyma of the right submandibular gland (arrows).

PowerPoint Presentation:

The submandibular excretory duct (Wharton duct) runs from the area of the submandibular gland hilum at the level of the border of the mylohyoid muscle, then bends around the free part of the mylohyoid muscle and extends to its orifice at the sublingual caruncle along the medial part of the sublingual gland. In general, a nondilated duct is not visible at US, but sometimes in slim individuals it may be visible.

(a) US image shows a nondilated Wharton duct (arrow) in a slim patient. Arrowheads = submandibular gland, 1 = mylohyoid muscle. (b)Diagram shows the course of the Wharton duct (arrow). Arrowheads = submandibular gland, 1 = mylohyoid muscle, 2 = sublingual gland. :

(a) US image shows a nondilated Wharton duct (arrow) in a slim patient. Arrowheads = submandibular gland, 1 = mylohyoid muscle. (b) Diagram shows the course of the Wharton duct (arrow). Arrowheads = submandibular gland, 1 = mylohyoid muscle, 2 = sublingual gland.

PowerPoint Presentation:

In some patients (obese patients, those who have undergone neck irradiation), the submandibular parenchyma may suppress ultrasound waves to such an extent that it is not possible to show not only deeper-lying structures but also the lower outline of the submandibular gland.

Sublingual Gland:

Sublingual Gland The sublingual gland lies between the muscles of the oral cavity floor: the geniohyoid muscle, intrinsic muscles of the tongue, and hyoglossal muscle (medially) and the mylohyoid muscle. Its lateral side is adjacent to the mandible. On transverse sections, the shape of the sublingual gland is close to an oval; on sections parallel to the body of the mandible, the shape is longitudinal and lentiform. Along its medial part runs the excretory duct of the submandibular gland.

Transverse US image (a) and corresponding diagram (b) show the sublingual gland and its surrounding structures. White circle = Wharton duct, m = muscle. :

Transverse US image (a) and corresponding diagram (b) show the sublingual gland and its surrounding structures. White circle = Wharton duct, m = muscle.

INFLAMMATORY DISEASES:

Inflammatory diseases are the most common diseases affecting the major salivary glands. INFLAMMATORY DISEASES

Acute Inflammation:

Acute Inflammation Acute inflammation causes painful swelling of the salivary gland, often bilaterally. Viral salivary gland infections are the most common in children. A particular predilection for the salivary glands is shown by mumps virus and cytomegalovirus. Acute bacterial infections are usually caused by Staphylococcus aureus or oral flora. In acute inflammation, salivary glands are enlarged and hypoechoic. They may be inhomogeneous; may contain multiple small, oval, hypoechoic areas; and may have increased blood flow at US. Enlarged lymph nodes with increased central blood flow may be observed in acute inflammation of salivary glands

Power Doppler US image shows an acutely inflamed right submandibular gland (arrows) containing a stone (arrowhead) :

Power Doppler US image shows an acutely inflamed right submandibular gland (arrows) containing a stone (arrowhead) The gland is enlarged and hypoechoic with rounded edges and increased blood flow.

Gray-scale US image shows an acutely inflamed right parotid gland (arrows) in a 5-year-old child. :

Gray-scale US image shows an acutely inflamed right parotid gland (arrows) in a 5-year-old child. The gland is enlarged and inhomogeneous with multiple small, oval, hypoechoic areas (arrowheads). The position of the US probe is shown in the inset diagram.

Abscess:

Abscess During acute sialadenitis, abscess formation may take place. Predisposing factors include dehydration and excretory duct obstruction caused by stones or fibrosis . At clinical examination, abscesses may be difficult to detect. They usually manifest as painful swelling of the salivary gland with skin reddening . The typical fluctuation sign may be absent in about 70% of cases . At US, abscesses are hypoechoic or anechoic lesions with posterior acoustic enhancement and unclear borders. Central liquefaction may be distinguished as an avascular area or identified by means of moving debris. Hyperechoic foci due to microbubbles of gas may be seen within the abscess . Organized abscesses may be surrounded by a hyperechoic “halo”. US guidance is being used for therapeutic drainage

Chronic Sialadenitis:

Chronic Sialadenitis Chronic sialadenitis is clinically characterized by intermittent swelling of the gland, often painful, that may or may not be associated with food. In chronic inflammation, salivary glands are normal sized or smaller, hypoechoic, and inhomogeneous and usually do not have increased blood flow at US At US, chronic and sometimes acute sialadenitis in children , as well as acalculous submandibular gland sialadenitis in adults, have also been described as showing multiple small, round or oval, hypoechoic areas or lesions distributed throughout glandular parenchyma. The differential diagnosis in such cases includes sarcoidosis and other granulomatous diseases, Sjögren syndrome, disseminated lymphoma, hematogenous metastases, and benign lymphoepithelial lesions in human immunodeficiency virus (HIV)–positive patients

Power Doppler US image shows chronic inflammation of the left submandibular gland (arrowheads):

Power Doppler US image shows chronic inflammation of the left submandibular gland (arrowheads) The gland is inhomogeneous with decreased parenchymal echogenicity but without increased blood flow. Arrows = stones.

Chronic Sclerosing Sialadenitis :

Chronic Sclerosing Sialadenitis A special form of chronic sialadenitis that may mimic a malignant lesion, both clinically and at imaging, is chronic sclerosing sialadenitis (Küttner tumor). In Küttner tumor, diffuse involvement of the salivary gland (usually the submandibular gland) may occur, with multiple small hypoechoic foci scattered on a heterogeneous background of salivary tissue visible at US. Focal involvement may also be encountered, with a focal hypoechoic heterogeneous lesion within a normally shaped gland. In all doubtful cases, verification with fine-needle aspiration biopsy is recommended .

Granulomatous Sialadenitis :

Granulomatous Sialadenitis Granulomatous sialadenitis occurs only rarely. US features of granulomatous sialadenitis are nonspecific: single or multiple hypoechoic areas in an enlarged or normally sized gland or diffuse low echogenicity . Blood flow may be increased. Mycobacterial disease of major salivary glands may manifest as a salivary gland mass, clinically indistinguishable from a neoplasm . In the parenchymal type of tuberculosis, Chou et al described focal, intraparotid, nearly anechoic zones that might have a cavity or cavities within them. In necrotic caseous cavities, which appear very hypoechoic, no color flow signals can be detected at US, in contrast to most salivary tumors. Salivary gland actinomycosis may mimic a malignant tumor at US; it may manifest as a hypoechoic area with ill-defined margins

Lymph Nodes in Sialadenitis :

Lymph Nodes in Sialadenitis In acute or chronic inflammation, lymph nodes may be enlarged; however, their normal echo-structure (homogeneous cortex and hyperechoic central hilum) is preserved. Central blood vessels or short vessel segments may be visible. Increased central blood flow in lymph nodes may be observed in acute inflammation

Sialolithiasis :

Sialolithiasis Salivary stones are most often located in the submandibular gland (60%–90% of cases) and may be multiple . Parotid glands are affected in about 10%–20% of cases . On classic radiographs, intraglandular and small stones may be missed, and only about 20% of sialoliths are radiopaque . CT allows visualization of large stones but without their precise localization and without the possibility of assessment of the ducts . The standard technique for imaging of the submandibular duct and the intraglandular ductal system remains digital sialography . A novel, noninvasive, promising method appears to be MR sialography, which also gives very good results in detection of sialoliths. US is a noninvasive method, well-established in cases of clinical suspicion of sialolithiasis, and is used as a primary modality, particularly in Europe . Although some authors claim that sialoliths smaller than 2–3 mm may be overlooked because of the absence of acoustic shadow, these articles are from the 1980s and currently used machines have better resolution and detection possibilities . Sialolithiasis causes partial or total mechanical obstruction of the salivary duct, which results in recurrent swelling of a salivary gland during eating and may be complicated by bacterial infection . Sialoliths in the distal part of the submandibular duct (Wharton duct) may be palpable in the floor of the mouth. However, sialoliths in the proximal portion of the duct or in the parenchyma of salivary glands may be demonstrated only radiologically. US features of sialolithiasis include strongly hyperechoic lines or points with distal acoustic shadowing, which represent stones . In symptomatic cases with duct occlusion, dilated excretory ducts are visible .

US image obtained obliquely relative to the mandible:

US image obtained obliquely relative to the mandible It shows a sialolith (arrowheads) in the inflamed parenchyma of the right submandibular gland (dashed line), which appears hypoechoic and inhomogeneous. The intraglandular excretory duct (arrows) above the stone is dilated. T = tongue.

PowerPoint Presentation:

When sialolithiasis of the submandibular gland is suspected, US may demonstrate whether the stone is located in the glandular parenchyma or in the Wharton duct. This distinction is essential for choosing the method of treatment.

US image shows a stone (arrows) in the dilated Wharton duct (arrowheads) near its orifice at the sublingual caruncle.:

US image shows a stone (arrows) in the dilated Wharton duct (arrowheads) near its orifice at the sublingual caruncle. M= acoustic shadow behind the surface of the body of the mandible. The position of the US probe is shown in the inset diagram.

PowerPoint Presentation:

In chronic ductal sialolithiasis complicated by chronic or recurrent inflammation, the gland may lose its function. At this stage of disease, stones located in a nondilated duct may be difficult to demonstrate. Stones located near the duct orifice or in the middle part of the Wharton duct may sometimes be better demonstrated when additional pressure is administered from inside the oral cavity during US examination. In about 50% of patients, sialolithiasis coexists with inflammation. Hyperechoic bubbles of air mixed with saliva may mimic stones in the Wharton duct and thus be a diagnostic pitfall.

US image shows hyperechoic linear structures (arrows), which may be mistaken for sialoliths in the Wharton duct.:

US image shows hyperechoic linear structures (arrows), which may be mistaken for sialoliths in the Wharton duct. These structures represent air bubbles in the oral cavity. Note the “dirty” (not purely anechoic) shadow behind the hyperechoic lines and points. Arrowheads = submandibular gland.

Sialosis:

Sialosis Sialosis is a noninflammatory, nonneoplastic, recurrent, painless salivary gland swelling, usually bilateral, which most often concerns the parotid glands. Sialosis has been described in connection with endocrine diseases, malnutrition, hepatic cirrhosis, chronic alcoholism, or different deficiency diseases (eg, avitaminoses) . US reveals enlarged, hyperechoic salivary glands with a poorly visible deep lobe but without focal lesions or increased blood flow

Sjögren syndrome:

Sjögren syndrome Sjögren syndrome is a chronic autoimmune disease predominantly affecting women over 40 years of age. It is characterized by intense lymphocytic and plasma cell infiltration and destruction of salivary and lacrimal glands . Major clinical symptoms include a dry mouth and eyes. Advanced stages of Sjögren syndrome may be recognizable at US examination of the parotid and submandibular glands . The disease may affect all salivary glands. US features of advanced Sjögren syndrome include inhomogeneous structure of the gland with scattered multiple small, oval, hypoechoic or anechoic areas, usually well defined, and increased parenchymal blood flow . Hypoechoic or anechoic areas are believed to represent infiltration by lymphatic cells, destroyed salivary parenchyma, and dilated ducts.

Gray-scale (a)and power Doppler (b) US images show advanced-stage Sjögren syndrome in the parotid gland.:

Gray-scale (a) and power Doppler (b) US images show advanced-stage Sjögren syndrome in the parotid gland. The gland has an inhomogeneous structure with multiple small, oval, hypoechoic areas (arrowheads) and increased blood flow. The position of the US probe is shown in the inset diagram.

PowerPoint Presentation:

Sjögren syndrome is frequently associated with both reactive and neoplastic lymphoproliferative disease. Further US monitoring for early detection of possible lymphomatous change is required in patients with Sjögren syndrome. Biopsy is recommended for lesions exceeding 2 cm or fast-growing lesions. Differential diagnosis of Sjögren syndrome with disseminated lymphoma in salivary glands may be challenging. Non-Hodgkin lymphoma manifesting as small multiple nodular disseminations with hypervascularization in the salivary gland has been reported. In addition, bilateral inflammation (acalculous), granulomatous disease (eg, sarcoidosis), hematogenous metastases, and benign lymphoepithelial lesions in HIV-positive patients should be taken into consideration in cases of multiple hypoechoic areas scattered in salivary gland parenchyma

NEOPLASMS:

Salivary gland neoplasms are relatively rare. Most of them are benign (70%–80%) and found in the parotid glands (80%–90%). About 10%–12% of all salivary gland neoplasms are located in the submandibular glands, but almost half of these neoplasms may be malignant. NEOPLASMS

Benign Neoplasms :

Benign Neoplasms The most common benign neoplasms of major salivary glands are pleomorphic adenomas (mixed tumor) and Warthin tumors (adenolymphoma, cystadenolymphoma, papillary cystadenoma lymphomatosum). Clinically, they manifest as slowly growing painless masses . However, small lesions may be detected incidentally at US. When their US appearance is analyzed, many common features may be found, but definitive differential diagnosis is usually not possible with US even between benign and malignant tumors. Pleomorphic Adenoma.— Pleomorphic adenomas occur most often in the parotid gland (60%–90%) in people in the fourth and fifth decades of life but may arise at any age. There is a slight predominance in women . Pleomorphic adenomas are usually solitary and unilateral . They grow slowly and may be asymptomatic. Nontreated pleomorphic adenomas may undergo malignant transformation after decades . In exceptional cases, pleomorphic adenomas may be clinically aggressive; they may metastasize and even be fatal . At US, pleomorphic adenomas are hypoechoic, well-defined, lobulated tumors with posterior acoustic enhancement and may contain calcifications. The feature of lobulated shape is being emphasized in differential diagnosis

Gray-scale US image shows the typical appearance of a pleomorphic adenoma (arrows).:

Gray-scale US image shows the typical appearance of a pleomorphic adenoma (arrows). The lesion is hypoechoic and lobulated with distinct borders and posterior acoustic enhancement.

 US image shows an inhomogeneous pleomorphic adenoma (arrows):

US image shows an inhomogeneous pleomorphic adenoma (arrows)

PowerPoint Presentation:

Vascularization in pleomorphic adenomas is often poor or absent (even when the sensitive power Doppler mode is used) but may be abundant . After inadequate surgery, pleomorphic adenomas often recur, usually multifocally

Power Doppler US image shows a pleomorphic adenoma (arrows) in the lower pole of the parotid gland. No blood vessels are visible in the lesion. :

Power Doppler US image shows a pleomorphic adenoma (arrows) in the lower pole of the parotid gland. No blood vessels are visible in the lesion.

PowerPoint Presentation:

Warthin Tumor.— Warthin tumor is the next most common benign salivary neoplasm (5%–10% of all benign salivary neoplasms) . It arises most often in men in the fifth and sixth decades of life . The relationship between smoking and development of Warthin tumors has been proved . Warthin tumor is usually solitary, unilateral, and slow growing. In about 10%–60% of cases, tumors may occur bilaterally or multifocally, sometimes metachronously, growing and manifesting clinically at different times . Sporadically, the epithelial component of Warthin tumor may undergo malignant transformation. At US, Warthin tumors are oval, hypoechoic, well-defined tumors and often contain multiple anechoic areas . Warthin tumors are often hypervascularized but may also contain only short vessel segments.

Gray-scale US image shows the typical appearance of a Warthin tumor (arrows).:

Gray-scale US image shows the typical appearance of a Warthin tumor (arrows). The lesion, which is located in the lower pole of the parotid gland, is oval, well defined, hypoechoic, and inhomogeneous with multiple irregular anechoic areas (arrowheads) and posterior acoustic enhancement.

Panoramic gray-scale US image shows two Warthin tumors (arrows) in the lower pole of the left parotid gland.:

Panoramic gray-scale US image shows two Warthin tumors (arrows) in the lower pole of the left parotid gland. The lesions are oval, well defined, hypoechoic, and inhomogeneous.

PowerPoint Presentation:

Diagnosis of a Warthin tumor may be supported by results of technetium 99m scintigraphy, which reveals a “hot” tumor because of the increased uptake of the tracer by the tumor . However, some other parotid neoplasms, benign as well as malignant, may sporadically show uptake of the radionuclide. Lobulated shape in pleomorphic adenomas and anechoic areas in Warthin tumors, although common, are not pathognomonic and may be found in many other lesions, including malignancies . For example, macroscopic cystic structures, which appear as anechoic areas at US, may occur in other benign tumors (pleomorphic adenoma, basal cell adenoma), in malignant tumors (mucoepidermoid carcinoma, acinic cell carcinoma), and in an abscessed or necrotic metastatic node; in addition, benign lymphoepithelial lesions in HIV-positive patients may have the appearance of solid-cystic nodules . Warthin tumor may also appear in the form of a simple cyst at US and thus require differentiation from cystic carcinomas (mucoepidermoid carcinoma, acinic cell carcinoma) and benign cysts (lymphoepithelial cysts)

Power Doppler US image shows a hypervascularized Warthin tumor (arrows) in the parotid gland. :

Power Doppler US image shows a hypervascularized Warthin tumor (arrows) in the parotid gland.

US image shows a pleomorphic adenoma (arrows) with an anechoic area (arrowheads), an appearance that mimics a Warthin tumor. :

US image shows a pleomorphic adenoma (arrows) with an anechoic area (arrowheads), an appearance that mimics a Warthin tumor.

PowerPoint Presentation:

Other Benign Tumors.— Other benign tumors (eg, oncocytoma, basal cell adenoma) occur less frequently in the salivary glands. Their differentiation is not possible with US. Among nonepithelial lesions, hemangiomas, lipomas, and neurinomas or schwannomas may be found in salivary glands

Panoramic gray-scale US image shows the typical appearance of a lipoma (arrowheads).:

Panoramic gray-scale US image shows the typical appearance of a lipoma (arrowheads). The lesion, which is located in the left parotid gland (arrows), is hypoechoic with regularly distributed linear structures. 1 = echo from the surface of the ramus of the mandible, 2 = masseter muscle.

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Hemangiomas, the most frequent tumors in infants, may manifest as heterogeneous lesions with sinusoidal spaces and calcifications representing phleboliths . Lipomas are usually oval and hypoechoic with sharp margins and hyperechoic linear structures regularly distributed within the lesion in a striated or feathered pattern . At color or power Doppler US, only single vessel segments may be found . In infants with hemangioma, US may show a homogeneous, mildly lobulated mass with a lobular structure, fine echogenic septa, and extremely high vascularization at color Doppler imaging. Other vascular lesions, such as pseudoaneurysms or arteriovenous fistulas, may also be encountered in the parotid gland, although they are rare. Neurogenic tumors often contain anechoic areas

Malignant neoplasm:

Malignant neoplasm The most common malignant neoplasms occurring in salivary glands are mucoepidermoid carcinoma and adenoid cystic carcinoma. Squamous cell carcinoma, acinic cell carcinoma, and adenocarcinoma are less common. Less than 30% of focal lesions in the parotid gland are malignant, whereas almost 50% of focal lesions in the submandibular gland are malignant. Unlike benign salivary neoplasms, malignant tumors may grow rapidly, may be tender or painful at palpation, may be fixed to the background, and may cause facial nerve paresis or paralysis

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Mucoepidermoid carcinoma occurs mostly between 30 and 50 years of age. Mucoepidermoid carcinoma may show several levels of differentiation and thus different tendencies to infiltration, metastases, and progress; the poorly differentiated form is extremely aggressive. The macroscopic appearance of the tumor, and similarly its imaging features, depend mostly on the level of malignancy. Well-differentiated tumors may be similar to benign tumors at US. Adenoid cystic carcinoma, which is a slowly growing tumor, shows a particular tendency to nerve infiltration (and thus pain), and late metastases are frequent . Classic US features of poorly differentiated or advanced malignant neoplasms of salivary glands are like those in other organs or tissues. US features of malignant salivary neoplasms include the following: an irregular shape, irregular borders, blurred margins, and a hypoechoic inhomogeneous structure. However, malignant tumors may also be homogeneous and well defined. The internal structure of a malignant tumor at US may be not only solid but also cystic or cystic with a mural solid nodule. Malignant tumors may have a lobulated shape, similar to that of pleomorphic adenomas

Panoramic gray-scale US image shows an acinic cell carcinoma (arrowheads) in the left parotid gland (solid arrows). :

Panoramic gray-scale US image shows an acinic cell carcinoma (arrowheads) in the left parotid gland (solid arrows). The tumor is well defined and has regular margins; however, there are signs of mandibular destruction (open arrows), a finding that suggests malignancy.

Panoramic gray-scale US image shows metastatic lymph nodes (open arrows), which are oval or round and inhomogeneous without hyperechoic hila:

Panoramic gray-scale US image shows metastatic lymph nodes (open arrows), which are oval or round and inhomogeneous without hyperechoic hila There is a primary adenocarcinoma (arrowheads) in the left parotid gland (solid arrows).

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Vascularization of malignant tumors is not pathognomonic, and assessment with color Doppler or power Doppler US does not allow reliable differentiation between benign and malignant salivary gland tumors . However, Schick et al report that high vascularization and high systolic peak flow velocity should raise the suspicion of malignancy. On the other hand, Bradley et al conclude that tumors demonstrating an increased intratumoral vascular resistance index have an increased risk of malignancy. The presence of metastatic-appearing lymph nodes accompanying a tumor in the salivary gland strongly suggests a malignancy. Very rarely, malignant tumors may occur multifocally or bilaterally, sometimes metachronously, or may coexist with benign neoplasms . An important problem in US is caused by small malignant neoplasms and metastases, less than 20 mm in diameter, and well-differentiated malignant neoplasms because they may demonstrate benign features: clear, even margins and homogeneous structure. These tumors also cause similar diagnostic problems with other diagnostic methods (CT and MR imaging)

 US image shows an oval, well-defined, homogeneous tumor with even margins (arrows) in the right submandibular gland:

US image shows an oval, well-defined, homogeneous tumor with even margins (arrows) in the right submandibular gland The parenchyma of the gland (arrowheads) has been changed by therapeutic neck irradiation. Despite its benign features, the tumor proved to be a metastasis from a squamous cell carcinoma at the base of the tongue.

Metastases:

Metastases Salivary glands are very uncommonly sites of metastases. Primary tumors metastasizing to salivary glands may be located in the head and neck region, as well as in more distant parts of the body. Melanoma, spinocellular cancer, breast cancer, and lung cancer may produce metastases to intraparotid lymph nodes. Extremely rare are metastases from renal cancer. At US, metastases may be well defined and oval. It may be difficult to differentiate multiple metastatic lesions from some patterns of inflammation, Sjögren syndrome, and granulomatous disease at US

 Power Doppler US image shows a metastasis (arrowheads) to the superficial lobe of the parotid gland (arrows) from a melanoma:

Power Doppler US image shows a metastasis (arrowheads) to the superficial lobe of the parotid gland (arrows) from a melanoma The tumor is lobulated, inhomogeneous, and virtually anechoic with posterior acoustic enhancement and chaotic, mainly peripheral vessel segments.

Lymphoma:

Lymphoma Salivary glands may also be affected by lymphoma. However, primary involvement of salivary glands is rare; they are usually one of the sites of systemic disease. Clinically, salivary lymphomas most often manifest as a painless, progressive swelling. They are usually associated with autoimmune disease, most often with Sjögren syndrome, sometimes also with rheumatoid arthritis

US image of a patient with follicular lymphoma shows affected lymph nodes (arrowheads) in the parotid gland (arrows = external outline of the superficial lobe).:

US image of a patient with follicular lymphoma shows affected lymph nodes (arrowheads) in the parotid gland (arrows = external outline of the superficial lobe). Affected nodes were also located beneath and along the sternocleidomastoid muscle.

PowerPoint Presentation:

At US of cases of lymphoma in the salivary gland, one may observe a solitary, hypoechoic, homogeneous or inhomogeneous lesion, which is oval or lobulated or has irregular margins and sometimes contains echogenic septa or stripes. However, these features are not pathognomonic, and lymphoma may not be reliably differentiated from other neoplastic or nonneoplastic salivary gland tumors with US. A pattern of multiple hypoechoic lesions with increased blood flow may also be seen. Such a pattern requires differentiation from inflammation, Sjögren syndrome, granulomatous disease (eg, sarcoidosis), and hematogenous metastases. In cases of lymphoma, solitary or multiple salivary gland lesions sometimes associated with microcysts may be observed at CT or MR imaging. Multiple lesions simulating Sjögren syndrome may also be difficult to diagnose with other imaging methods (eg, MR imaging) . At gray-scale US, lymphomatous lymph nodes may demonstrate all the US features of a simple cyst

Gray-scale US image of a patient with non-Hodgkin lymphoma shows a lymphomatous lymph node (arrows) in the parotid gland.:

Gray-scale US image of a patient with non-Hodgkin lymphoma shows a lymphomatous lymph node (arrows) in the parotid gland. The oval, well-defined, anechoic lesion demonstrates discrete posterior enhancement and mimics a simple cyst.

Cysts:

Cysts Simple cysts are uncommon in salivary glands. They may be congenital or acquired. Some acquired cysts develop due to obstruction of the salivary ducts in the presence of a tumor, stones, or inflammation. Clinically, they usually manifest as a painless swelling but may be tender when infected. US features of a cyst are classic (like in any other location in the body): well-defined margins, anechoic content, posterior acoustic enhancement, and no evidence of internal blood flow at power Doppler or color Doppler imaging

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Benign lymphoepithelial lesions in HIV-positive patients may manifest as multiple cysts . Possible diagnostic pitfalls include a “pseudocystic” appearance of lymphoma, the cystic form of Warthin tumor, lymphoepithelial lesions, or metastatic lymph nodes with a central fluid collection or necrosis

Gray-scale tissue harmonic US image shows a simple cyst (arrowheads) in the lower pole of the parotid gland (arrows). :

Gray-scale tissue harmonic US image shows a simple cyst (arrowheads) in the lower pole of the parotid gland (arrows).

Effects of irradiation:

Effects of irradiation The major salivary glands are often irradiated during radiation therapy of head and neck neoplasms. A major adverse effect of such treatment is xerostomia caused by functional and structural impairment of salivary parenchyma . Loss of salivary gland function significantly diminishes the patient’s quality of life. The most useful method for evaluation of salivary excretory function remains scintigraphy, especially single photon emission CT (SPECT). Carbon 11–methionine positron emission tomography (PET) offers new possibilities for studying the individual response of major salivary glands to irradiation . After irradiation, salivary glands become hypoechoic and inhomogeneous at US . The salivary glands enlarge in the acute phase and later become smaller because of atrophy . Postirradiation edema corresponding to sialadenitis is well visible on T2-weighted MR images .

Trauma:

Trauma Traumatic injuries of the salivary glands occur most often in the parotid gland because the other major salivary glands are protected by the mandible. After salivary gland trauma, US may demonstrate a hematoma, other fluid collections ( eg , a sialocele ), or a fistula in the parotid gland or surrounding structures . Suspected damage to the facial nerve or Stenon duct warrants application of other imaging modalities (CT, MR, sialography )

Conclusion:

Conclusion Ultrasound is an inexpensive, non-invasive and readily available imaging technique, that can be used as an primary investigative imaging technique so as to avoid radiation hazards caused by x-ray radiation (or) MRI which may be highly economical to the patients. So proper application and utilization of this technique can be of great use in dentistry.

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