Radiology for the surgeon: soft-tissue case 59

• Published in: Canadian Journal of Surgery 2006-12, Vol.49 (6), p.435-436
• Main Authors: Ng, Simon S.M, Hon, Sophie S.F, Wong, Joseph H.M, Lee, Janet F.Y
• Format: Article
• Language: English
• Subjects: Continuing Medical Education; Cysts; Genetic disorders; Medical diagnosis; NMR; Nuclear magnetic resonance; Radiology; Sexual disorders; Surgery
• ISSN: 0008-428X; 1488-2310

Magnetic resonance imaging (MRI) of the pelvis demonstrated a wellcircumscribed, homogeneous and unilocular cystic lesion 13×10×8 cm in size in the left ischiorectal fossa. The lesion demonstrated high signal intensity on T^sub 2^-weighted images. No intralesional solid component or debris was noted. Medially, the lesion displaced the vagina and the anal canal contralaterally (Fig. 4, arrows); superiorly, the lesion elevated the levator ani muscles without direct intraabdominal extension (Fig. 5, arrows). No definite communication between the cystic lesion and the spinal canal was seen. Differential diagnoses included epidermal cyst, Gartner duct cyst, rectal duplication cyst and tailgut cyst. Ischiorectal fossa epidermal cysts are usually unilocular and have high signal intensity on T^sub 2^-weighted MRI. They are lined by stratified squamous epithelium and contained keratin material. They are generally small, but several cases of giant epidermal cysts affecting the ischiorectal fossa with a diameter of 5 cm or more have been reported in the literature.2 The differential diagnoses of ischiorectal fossa epidermal cyst on MRI include Gartner duct cyst, rectal duplication cyst and tailgut cyst. Gartner duct cysts are congenital lesions resulting from incomplete regression of the Wolffian ducts. They are usually confined to the vaginal walls, but the larger cysts can extend into the ischiorectal fossa. The MRI features of Gartner duct cysts are very similar to that of epidermal cysts.3 Rectal duplication cysts are also unilocular on MRI, but they are attached to the alimentary tract. They are lined by epithelium similar to that of the alimentary tract and possess a smooth muscle coat.4 Tailgut cysts are uncommon congenital lesions caused by incomplete regression of the embryonic tailgut. On MRI, tailgut cysts are usually multilocular instead of unilocular, and they show high-signal intensity on T^sub 2^-weighted images.5 Both rectal duplication cysts and tailgut cysts have the potential for malignant transformation; thus it is essential to differentiate these lesions from benign epidermal cysts.4,5