Figure 1. Contrast computed tomography reveals a hypodense cystic lesion
measuring about 99*93 mm in the left retro-rectal region (arrowhead)
without contrast enhancement, causing a rectal deviation to the right
side.
She underwent surgical cystectomy drainage and incomplete resection of
the cyst. Histopathologic examination showed a cyst wall containing
smooth muscle bundles lined by squamous or columnar epithelium. The
stroma was infiltrated by nests of neoplastic cells with vesicular
nuclei and abundant eosinophilic cytoplasm with foci of keratin-like
material (Figure 2). In immunohistochemical staining, CK7, HMWCK, and
P63 were positive, but CK20 was negative. These findings were compatible
with squamous cell carcinoma arising on tailgut cyst.