Читать книгу Salivary Gland Pathology - Группа авторов - Страница 104

Intraglandular lymph nodes are found in the parotid gland due to its early encapsulation during development. The sublingual gland and submandibular gland do not contain lymph nodes. The parotid and periparotid lymph nodes are the first order nodal site for lesions that affect the scalp, skin of the upper face, and external ear (Ollila et al. 1999). The most common malignancy to metastasize to the parotid nodes is squamous cell carcinoma followed by melanoma and, less commonly, Merkel cell carcinoma (Bron et al. 2003) (Figures 2.82 through 2.84 ).

Figure 2.79. Axial CT scan with contrast at the level of the parotid tail demonstrating an ill‐defined heterogeneously enhancing mass adjacent to or exophytic from the parotid tail medially (arrow). Lymphoma in cervical lymphadenopathy was diagnosed at surgery.

Figure 2.80. Axial PET scan image corresponding to the case in Figure 2.79. A large mass of the left parotid gland (arrow) is noted.

Figure 2.81. Fused axial PET/CT image corresponding to the case illustrated in Figure 2.79.

Figure 2.82. Axial CT of a mass in the right parotid gland with homogenous enhancement. The patient had a history of right facial melanoma. Metastatic melanoma was diagnosed at surgery.

The imaging findings are not specific. CT in early stages demonstrates the nodes to have sharp margins, round or ovoid architecture but without a fatty hilum. Late in the disease, mass can mimic infected or inflammatory nodes with heterogenous borders, enhancement, and necrosis. Late in the disease with extranodal spread, the margins blur and are ill‐defined. Contrast enhancement is heterogenous. Similar findings are seen on MRI with T1 showing low to intermediate signal pre‐contrast and homogenous to heterogenous signal post‐contrast depending on intranodal versus extranodal disease. PET with FDG is abnormal in infectious, inflammatory, and neoplastic etiology and is not typically helpful within the parotid, but can aid in localizing the site of the primary lesion as well as other sites of metastases. This can be significant since the incidence of clinically occult neck disease is high in skin cancer metastatic to the parotid gland (Bron et al. 2003). Local failure was highest with metastatic squamous cell carcinoma and distant metastases were higher in melanoma (Bron et al. 2003).

Figure 2.83. Axial PET scan corresponding to the case illustrated in Figure 2.82. The mass in the right parotid gland (arrow) is hypermetabolic. Note two foci of intense uptake corresponding to inflammatory changes in the tonsils.

Figure 2.84. Axial contrast‐enhanced CT scan through the parotid glands demonstrating a large mass of heterogenous density and enhancement partially exophytic from the gland. Metastatic squamous cell carcinoma from the scalp was diagnosed.

With either squamous cell carcinoma or melanoma, there is also a concern for perineural invasion and spread. Tumors commonly known to have perineural spread in addition to the above include adenoid cystic carcinoma, lymphoma, and schwannoma. The desmoplastic subtype of melanoma has a predilection for neurotropism (Chang et al. 2004). The perineural spread along the facial nerve in the parotid gland and into the skull base at the stylomastoid foramen must be carefully assessed. MRI with contrast is the best means of evaluating the skull base foramina for perineural invasion. Gadolinium contrast‐enhanced T1 MRI in the coronal plane provides optimal view of the skull base (Chang et al. 2004). There may also be symptomatic facial nerve involvement with lymphadenopathy from severe infectious adenopathy, or inflammatory diseases such as sarcoidosis.