Image of the Month—Quiz Case

A 43-year-old man was referred to our institution with lower abdominal pain and perineal swelling and fullness of more than a year. At the referring hospital, he underwent a nondiagnostic computed tomography–guided biopsy of what was presumed to be a large pilonidal cyst. His medical history was unremarkable for hematochezia or alteration in bowel function. Magnetic resonance imaging at our institution revealed a 14 × 10.5 × 25-cm bilobed, cystic mass situated in his pelvic outlet in the retrorectal space, markedly compressing his rectum (Figure 1and Figure 2). There was a suggestion of internal hemorrhagic vs proteinaceous debris with degenerative changes within the mass and enhancing mural nodules. The mass extended through the floor of the pelvis and into the perineal area. It did not appear to invade his rectum or involve the regional vasculature.

Figure 1. 

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A sagittal T2-weighted magnetic resonance image demonstrates the bilobed retrorectal mass compressing the adjacent structures. The arrow indicates the compressed rectum, and the asterisk indicates the bladder.

Figure 2. 

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A coronal digital subtraction magnetic resonance image demonstrates multiple enhancing mural nodules on the mass indicated by the arrow.

A. Enteric duplication cyst

B. Complex pilonidal cyst

C. Retrorectal cystic hamartoma (tailgut cyst)

D. Perirectal abscess

Answer