Salivary Gland Pathology. Группа авторов
can be like that of lymphoepithelial lesions seen with HIV but does include calcifications. Typically, there is no diffuse cervical lymphadenopathy. The development of cervical adenopathy may indicate development of lymphoma (Takashima et al. 1992). Solid nodules or masses can also represent underlying lymphoma (non‐Hodgkin type) to which these patients are prone (Sugai 2002). The latter stages of the disease produce a smaller and more fibrotic gland (Shah 2002; Bialek et al. 2006; Madani and Beale 2006a).
Figure 2.56. Reformatted coronal contrast‐enhanced CT of the submandibular gland demonstrating a sialolith in the hilum of the right submandibular gland.
Figure 2.57. Axial contrast‐enhanced CT of the parotid gland demonstrating a small left parotid sialolith (arrow).
Figure 2.58. Axial contrast‐enhanced CT at the level of the submandibular glands with a very large left hilum sialolith (arrow).
SARCOIDOSIS
Sarcoidosis is a granulomatous disease of unknown etiology (see Chapter 6). It typically presents with bilateral parotid enlargement. It may be an asymptomatic enlargement or may mimic a neoplasm with facial nerve palsy. The parotid gland usually demonstrates multiple masses bilaterally, which is a nonspecific finding and can also be seen with lymphoma, tuberculosis (TB) or other granulomatous infections, including cat‐scratch disease. There is usually associated cervical lymphadenopathy. The CT characteristics of the masses are slightly hypodense to muscle but hyperdense to the more fatty parotid gland. MRI also demonstrates nonspecific findings. Doppler US demonstrates hypervascularity, which may be seen with any inflammatory process. The classically described “panda sign” seen with uptake of 67Ga‐citrate in sarcoidosis is also not pathognomonic for this disease and may be seen with Sjögren syndrome, mycobacterial diseases, and lymphoma.
CONGENITAL ANOMALIES OF THE SALIVARY GLANDS
First Branchial Cleft Cyst
This congenital lesion is in the differential diagnosis of cystic masses in and around the parotid gland along with lymphoepithelial lesions, abscesses, infected or necrotic lymph nodes, cystic hygromas, and Sjögren syndrome. Pathologically, the first branchial cleft cyst is a remnant of the first branchial apparatus. Radiographically, it has typical characteristics of a benign cyst if uncomplicated by infection or hemorrhage, with water density by CT and signal intensity by MRI. It may demonstrate slightly increased signal on T1 and T2 images if the protein concentration is elevated and may be heterogenous if infected or hemorrhagic. Contrast enhancement by either modality is seen if infection is present. Ultrasound demonstrates hypoechoic or anechoic signal if uncomplicated and hyperechoic if infected or hemorrhagic. There is no increase in FDG uptake unless complicated. Anatomically, it may be intimately associated with the facial nerve or branches. They are classified as type I (Figure 2.59) (less common of the two types) if found in the external auditory canal and type II if found in the parotid gland or adjacent to the angle of the mandible (Figure 2.60) and may extend into the parapharyngeal space. It may have a fistulous connection to the external auditory canal or the skin surface. Infected or previously infected cysts may mimic a malignant tumor. Although not typically associated with either the parotid or submandibular glands, the second branchial cleft cyst, which is found associated with the sternocleidomastoid muscle and carotid sheath, may extend superiorly to the tail of the parotid or anteroinferiorly to the posterior border of the submandibular gland. It has imaging characteristics like the first branchial cleft cyst. Therefore, the second branchial cleft cyst must be differentiated from cervical chain lymphadenopathy or exophytic salivary masses. The third and fourth branchial cleft cysts are rare and are not associated with the salivary glands and are found in the posterior triangle and adjacent to the thyroid gland, respectively (Koeller et al. 1999).
Figure 2.59. Axial contrast‐enhanced CT (a) of the head with a cystic mass at the level of the left external auditory canal and sagittal T2 MRI of a different patient (b) consistent with a type 1 branchial cleft cyst.
NEOPLASMS – SALIVARY, EPITHELIAL
Benign
Pleomorphic adenoma
Pleomorphic adenoma (PA) is the most common tumor of the salivary glands and is comprised of epithelial, myoepithelial, and stromal components. It is also the most common benign tumor of the minor salivary glands (Jansisyanant et al. 2002). Most commonly unilateral, lobulated and most commonly sharply marginated, the PA can vary in size and be up to 8 cm long and involve superficial and deep parotid lobes. The lobulated regions are sometimes referred to as a “cluster of grapes” (Shah 2002). The majority (80%) exist in the superficial lobe of the parotid gland. Small lesions are better circumscribed, have homogenous enhancement, and are of uniform soft tissue density (skeletal muscle). There can be mild to moderate enhancement and the lesion is relatively homogenous. The larger lesions have heterogenous density, enhancement pattern, and low attenuation foci from necrosis and cyst formation as well as calcification. The T1 signal can be as variable as the density on CT but tends to follow muscle or soft tissue signal against a background of fat of the normal parotid gland (Figure 2.61). The masses may be hypointense when small, and then become heterogenous with the cystic and calcific changes, and can be hyperintense secondary to areas of hemorrhage and calcifications. The T2 imaging characteristic is that of high signal intensity, with a thin low signal rim, except when hemorrhage may cause the signal to be heterogenous. The cystic or necrotic regions will tend to be low to intermediate signals on T1 and high on T2. There is mild homogenous enhancement when small and heterogenous when large. US usually demonstrates a homogenous hypoechoic mass but may also have heterogenous hypoechoic features with slight increase in thru transmission (Madani and Beale 2006b). These features may be shared with other benign and malignant lesions but only tumors that have both lobulation of the contour and a well‐defined pseudocapsule are benign (Ikeda et al. 1996). The tumor components, cellular or myxoid, determine the MRI signal. The hypercellular regions have lower signal on T2 and STIR sequences as well as reduced ADC values on DWI and earlier TIC (time versus signal intensity curves) peak on dynamic MRI (Motoori et al. 2004). The high cellular components may be seen with other tumor types including malignant types. The myxoid components, which are more diagnostic of PAs, result in high T2 and STIR signal, high ADC values on DWI, and progressive enhancement on dynamic MRI (Motoori et al. 2004). In fact, of the three types of PAs, myxoid, cellular, and classic, the myxoid is the most common the most likely to recur (Moonis et al. 2007). MRI with T2 and STIR sequences has been shown to be quite sensitive in detecting recurrent PA of the myxoid type by demonstrating