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Radiodiagnosis of Salivary gland tumours Dr. Pankaj Kaira JR –II Radiodiagnosis SRMSIMS Bareilly, India
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Salivary glands have a glandular structure with tubules, secretory acini and myoepithelial cells to produce and secrete saliva. MAJOR SALIVARY GLANDS (paired structures): PAROTID SUBMANDIBULAR (SUBMAXILLARY) SUBLINGUAL MINOR SALIVARY GLANDS (diffusely scattered in the oral cavity, paranasal sinuses, pharynx and larynx) BUCCAL (cheek) PALATINE(palate) LABIAL(lip) LINGUAL(tongue) Secrete 10% of total volume of saliva Account for about 70% of mucus secreted
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Parotid gland drains via the Stenson's duct traversing superficial to the masseter muscle and passing through the buccinator muscle before finally opening into the oral cavity at the ipsilateral 2ndmaxillary molar.
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Submandibular gland is also called submaxillary gland. The submandibular gland is the second largest salivary gland and is located in the floor of the mouth adjacent to the posterior body of mandible along the free edge of the mylohyoid muscle. Partially enclosed between two layers of the deep cervical fascia. The amount of adipose tissue is relatively lower than that of parotid gland. The lingual nerve and submandibular ganglion are noted superficial to the submandibular gland while the hypoglossal nerve lies deep to it. It drains through the Wharton's duct in the anterior sublingual region at the papilla in paramidline location.
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Sublingual gland is the smallest major salivary gland. It lies submucosally adjacent to the anterior mandible in parasymphyseal location. The Wharton’s duct and lingual nerve separate the sublingual gland from the medial genioglossus muscle. It opens via multiple ducts usually 20 in number (known as ducts of Rivinus) directly into the floor of mouth along sublingual papillae and folds. Occasionally, some of the ducts unite to form the Bartholin’s duct that drain into the Wharton’s duct.
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Imaging Pain radiography Sialography Ultrasonography Computed Tomography (CT) Magnetic Resonance Imaging (MRI) Radionuclide scintigraphy
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SIALOGRAPHY It refers to the evaluation of the ductal system of the salivary glands. It is considered the gold standard technique for studying the ductal morphology. It is commonly used for parotid and submandibular glands and its main indication is chronic sialadenitis unrelated to sialolithiasis. Acute sialadenitis is a contraindication for sialography. Irregular pooling of contrast and ductal obstruction without presence of calculus are indirect signs of malignancy. 3DCT performed especially with cone-beam CT following injection of the contrast medium into the ductal system without intravenous injection of contrast can provide images similar to or better than conventional sialography and is often referred to as CT sialography. MR Sialography, by contrast, delineates the ductal system of the gland without injection of ductal/intravenous contrast by utilizing the highly fluid-sensitive sequences similar to that used for magnetic resonance cholangiopancreatography (MRCP).
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Ultrasonography It is a quick and noninvasive method of evaluating parotid and submandibular glands. Both glands appear homogeneously hyperechoic on HRUS, and retromandibular vein can be noted within the parotid gland. It is performed by a high-frequency linear (7-10 MHz) transducer. It helps in differentiating cystic from solid lesions and also aids in guiding the exact site of Fine Needle Aspiration Cytology (FNAC) in suspected salivary gland lesions. It fails to demonstrate the parotid gland in its entirety because of intervening mandible. It also does not clearly demonstrate the intraglandular facial nerve branches.
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Both glands have homogenous echo pattern with scattered echogenic steaks produced by branch ducts converging into main duct. When combined with color Doppler imaging, it helps in assessing the vascularity and nature of the lesion (malignant lesions of salivary glands are highly vascular as compared to their benign counterparts – peripheral vascularity with hypovascular central area in the tumoral lesion is highly suggestive of pleomorphic adenoma). RI and PI values of greater than 0.7 and 1.2, respectively, coupled with high PSV (greater than 44.3 cm/s), ill-defined margins, and nodal involvement with central vascularity are highly indicative of malignant salivary gland lesion.
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CT & MRI These cross-sectional studies help in true and near complete imaging of the salivary glands. MRI, because of its multiplanar capability and higher soft tissue resolution, has an upper hand over CT to assess the relationship of tumours with neighbour structures and detect if there is perineural, lymphatic or intracranial spread. The basic sequences are: T1-WI, T2FSE-WI, STIR or T1 with fat saturation and T1-WI after contrast. However, CT (especially cone-beam CT) demonstrates the osseous lesions/extension and calcification/calculus better than MRI and is used when inflammatory conditions are suspected. However, ductal system is not optimally evaluated by any of these techniques.
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Parotid glands have variable amounts of fatty stroma, thus have lower CT attenuation (-25 to +15HU) than adjacent muscles, LN and vessels. The submandibular glands have higher attenuation than the parotid glands but are still easily distinguished from the adjacent musculature. These studies are often performed after intravenous injection of the contrast media for better delineation of the anatomy and the extent of lesion. Diffusion-weighted (DW) images and gadolinium-enhanced dynamic MR (Gd-MRI) imaging have proven to be very useful in differentiating benign from malignant tumors. DW images can be used to calculate apparent diffusion coefficient (ADC) values, which are different for different salivary gland tumors.
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Gd-MR with dynamic imaging using 120 s as cut-off for time to peak enhancement and 30 % wash-out ratio can differentiate benign and malignant tumors as the latter take less time for peak enhancement and show rapid wash-out. Plateau type of time–intensity curve in dynamic Gd-MR coupled with low ADC values is also highly suggestive of malignancy. Proton MR Spectroscopy has also been described for differentiation of benign from malignant tumors by some authors. Choline/creatinine ratios are significantly lower in malignant than in benign salivary gland tumors
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PET SCAN Very sensitive for metastatic LN < 8mm Helpful for previously treated H + N cancers Positron emission tomography (PET) imaging using 2-deoxy-2-[18F] fluoro-d -glucose (FDG) can be used to differentiate benign from malignant tumors of the salivary glands as the former appear as cold spots with the exception of Warthin's tumor and oncocytoma. PET/CT Scan Has increased value in salivary gland tumour staging Pittsburgh study(55pts) showed sensitivity of 74.4% specificity of 100% Angiography or MRI-Angio Can be used to assess carotid artery involvement
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Radionuclide Imaging Scintigraphy with technetium (Tc) 99m pertechnetate is a dynamic and minimally invasive diagnostic test to assess salivary gland function and to determine abnormalities in gland uptake and excretion. Only the parotid and submandibular glands are visualized distinctly, as well as the thyroid gland, which binds and retains Tc. Uptake and secretion phases can be recognized on the scans. Uptake of Tc 99m by a salivary gland indicates that there is functional epithelial tissue present. With few exceptions, neoplasms arising within the salivary glands do not concentrate Tc 99m. The exceptions are Warthin’s tumor and oncocytomas, which arise from ductal tissue and are capable of concentrating the tracer.
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SALIVARY GLAND TUMOURS According to the World Health Organization there are nearly 40 different types of tumors that arise from salivary glands with a variable behaviour. The WHO classification divide them into epithelial and non- epithelial, benign and malignant
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WHO classification with the most common tumors of salivary glands, includes: Benign epithelial tumors: Pleomorphic adenoma, Warthin´s tumor, myoepithelioma, oncocytoma, ductal papilloma. Malignant epithelial tumors: Mucoepidermoid carcinoma, acinic cell carcinoma, adenoid cystic carcinoma, adenocarcinoma not otherwise specified, carcinoma ex pleomorphic adenoma. Benign non-epithelial tumors: Haemangioma, lymphangioma, lipoma. Malignant non epithelial tumors: Hodgkin´s lymphoma, diffuse large B-cell lymphoma, metastases.
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The distribution of the tumors is as follows: 80% in parotids, 10% in submandibulars, 1% in sublinguals and 5% in minor salivary glands.
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PLEOMORPHIC ADENOMA (Benign Mixed Tumour) Most common benign tumor in all salivary glands. It accounts for 50% of all salivary gland tumors and 80% of parotid tumors. They typically occur in middle-aged women. Usually solitary and unilateral. Slow-growing, painless mass. If untreated, 15% become malignant and occasionally metastatize to lymph nodes, lung, bone and brain.
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IMAGING : USG - Hypoechoic, well-defined, lobulated tumors with posterior acoustic enhancement and may contain calcifications. At doppler color study show peripheral vascularity with hypovascular center.
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CT - Smoothly marginated or lobulated homogeneous small spherical mass is the most common appearance. When larger they can be heterogeneous with foci of necrosis. Small regions of calcification are common. When small enhancement tends to be prominent. In larger tumours enhancement is less marked, but can demonstrate delayed enhancement. MRI They are commonly seen as well-circumscribed and homogeneous when small. Larger tumours may be heterogeneous. T1 - usually of low intensity T2 usually of very high intensity (especially myxoid type) often have a rim of decreased signal intensity on T2-weighted images representing the surrounding fibrous capsule T1 C+ (Gd) - usually demonstrates homogeneous enhancement. Show no restriction on DWI. Angiography (DSA) Typically hypovascular.
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WARTHIN TUMOUR Also known as adenolymphoma, cystadenolymphoma, papillary cystadenoma lymphomatosum. It arises from heterotopic parotid tissue within parotid lymph nodes. Second most common benign salivary neoplasm (5%–10%). It arises most often in men in the fifth and sixth decades of life. Warthin tumor is usually solitary, unilateral, and slow growing. In the differential diagnoses of multiple lesions, metastases, lymphoma or inflammatory disease must be considered.
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IMAGING: USG -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.
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CT: Classic appearance is a cystic lesion posteriorly within the parotid with a focal tumour nodule. relatively well defined cystic changes appear as intra lesion at lower attenuation, no calcification. MRI: Well defined and can be bilateral. T1 - low to intermediate signal with cyst containing cholesterol components containing focal high signal. T2 - heterogenous and variable signal intensity C+ (Gd) - usually no contrast enhancement . Scintigraphy: Often shows uptake with Tc99-pertechnetate, thallium and FDG-PET which reveals a “hot” tumor.
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Computed tomography of Warthin tumor. A: A large well-defined mass involves the superficial lobe of the left parotid gland. The mass enhances diffusely. B: At the level of the parotid tail, areas of lower density (arrowheads) are consistent with cystic components observed in the posterior aspect of the mass.
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Other benign lesions Haemangioma -. Non epithelial benign tumor with proliferation of benign blood vessels. It is the most common in children, and 80% affect to females. The majority presents an spontaneous involution. Imaging Findings: On US, they appear as a hypoechoic polilobulated infiltrating tumor with prominent internal vascular structures. It typically has phleboliths on CT and marked hyperintensity signal on T2WI in MRI. At MRI flow void in or around the mass may be present. It enhances avidly after contrast administration. Oncocitoma -. Rare tumors that arise from oncocytes derived from striated duct cells. Appear in elderly (>70years). Inespecific on imaging or similar to pleomorhic adenomas.
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T1-weighted axial (A) and T2-weighted axial images with fat saturation demonstrate enlargement and replacement of the left parotid gland by a cystic-appearing lesion. The lesion remains well encapsulated and has an enlarged flow void in the retromandibular vein consistent with a hemangioma
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A left parotid oncocytoma in a 68- year-old woman. CT scan reveals a large deformable tumor (white asterisk), which extends medially into the parapharyngeal space through the stylomandibular gap. The contour of the tumor is distorted by the styloid process (black arrow) and the left medial pterygoid muscle (black arrowheads).
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MUCOEPIDERMOID CARCINOMA The most common of malignant tumor. It´s about 10% of all salivary gland tumors and 50% of the malignant. It sets in the parotids (50%) and minor salivary glands (45%). Patients usually are 35-65 years old.
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USG : Typically a well circumscribed hypoechoic, with an either part of completely cystic appearance. The lesion stands out against the relatively hyperechoic normal parotid gland. CT : Low grade tumours appear as well circumscribed masses, usually with cystic components. The solid components enhance, and calcification is sometimes seen. They have appearances similar to benign mixed tumours. High grade tumours on the other hand, have poorly defined margins, infiltrate locally and appear solid. MRI : Again, imaging is dependent on grade. Low grade tumours have similar appearances to benign mixed tumors. T1 - low to intermediate signal ; low signal cystic spaces T2 - intermediate to high signal ; cystic areas will be high signal T1 C+ (Gd) - heterogeneous enhancement of solid components High grade tumours on the other hand have lower signal on T2 and poorly defined margins and infrequent cystic areas. T1 - low to intermediate signal T2 - intermediate to low signal
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Mucoepidermoid carcinoma of the parotid gland. Transverse CT scan shows an ill-defined mass (C) that has less attenuation than that of enhancing parotid tissue in the right parotid gland.
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Adenoid cystic carcinoma The most common malignant tumour in submandibular, sublingual and minor salivary glands. Equal incidence in male and females. Usually seen in 5th decade. It typically appears as an infiltrating mass with a high tendency to perineural and perivascular extension (50-60%). Very high recurrence rate after surgery.
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CT - well defined, low grade tumours can usually be differentiated from infiltrative, high grade tumours although homogeneous enhancement following contrast is common in both groups. MRI - especially useful for these tumours, due to their tendency for perineural spread. They generally have a hypointense appearance on T1 weighted imaging, a slightly hyperintense appearance on T2 weighted imaging and, similar to CT, enhance homogeneously.
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Acinic cell carcinoma It is the second most common malignant tumour of parotids in children. Slight female preference, around 40-60 years old. Can be multiple/bilateral. Its typical features are circumscribed solid or partially cystic lesions that may have a thin or incomplete capsule.
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Acinic cell carcinoma. MR shows a well-delimited nodular lesion (arrow) inside accessory parotid gland, localized lateral to the masseter muscle (M). This lesion is hyperintense in T2, hypointense in T1 and with homogeneous enhancement after de endovenous gadolinium administration. The definitive diagnose was anatomopathological (cystic acinic cell carcinoma),
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Lymphoma Lymphomas can present as a diffuse disease affecting the whole gland or as intraparotid adenopathies. Primary parotid lymphoma is a rare entity, so lymphoma usually involves parotid glands via haematogenous spread. The most common is non-Hodgkin lymphoma,and among them, large B-cell lymphoma. Its imaging features are wide and nospecific,ranging from nodes with "pseudocystic" appearance to large masses. They have the lowest ADC values in DWI-MRI.
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Non-contrast T1W axial images show intra-parotid adenopathy (white arrows) with altered appearance in a case of tuberculosis of left parotid gland.
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METASTASIS Metastases to salivary glands are mainly observed in the parotid gland due to the presence of intraglandular lymph nodes, which drain the face, external ear, and scalp. Skin malignancies (melanoma, squamous cell carcinomas) are the most common primary tumours metastasising to the salivary glands, therefore careful clinical examination has to be performed. However, other malignancies, such as renal cell carcinomas, lung, breast and gastrointestinal carcinomas can also metastasise to the parotid gland or periparotid lymph nodes.
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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.
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