Читать книгу Salivary Gland Pathology - Группа авторов - Страница 95

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.