Image of the Month—Diagnosis

Exploratory laparotomy and pelvic exploration with resection of the mass was performed. We approached the resection through a midline incision. Intraoperatively, we found a large, multicystic, fluid-filled mass that involved the superior rectal artery and significantly compressed the adjacent structures. The tumor was resected in continuity with the rectum and anus; a coccygectomy was also performed. No evidence was found of metastatic disease or lymphadenopathy.

Histologic examination of the specimen revealed a moderately differentiated adenocarcinoma with colorectal-type morphologic features arising within a tailgut cyst. The colorectal phenotype was confirmed immunohistochemically by positive stains for CDX2 and CK20 and a negative stain for CK7. Nine local lymph nodes were negative for malignant neoplasm. The surgical margins were free of malignant neoplasm. The patient elected to undergo adjuvant locoregional chemoradiotherapy, as recommended by our institutional tumor board.

A tailgut cyst, or retrorectal cystic hamartoma (RCH), is a rare congenital lesion that arises from vestiges of the most caudal portion of the primitive hindgut and typically presents as a retrorectal mass.^1,2This embryologic remnant usually regresses during the 7th to 8th week of development. These tumors occur most commonly in middle-aged women (3:1) and often have a nonspecific clinical presentation, with pain reported in 51% of patients.³The tumors often contain many types of epithelial tissue but always contain some elements of intestinal epithelium. An RCH rarely undergoes malignant transformation of the epithelial components of the tumor, but it nonetheless necessitates meticulous gross and microscopic evaluation of the surgical specimen to rule out malignant neoplasm. In 2000, Prasad et al⁴noted 12 cases in the literature of a malignant neoplasm within an RCH. We identified 14 more through June 2006 and, including our case, 26 cases of malignant transformation within an RCH have been reported during the past 75 years; 17 were adenocarcinomas^2,4-9and 9 were carcinoid tumors.⁹An elevated preoperative carcinoembryonic antigen level may indicate malignant transformation and may be useful in tracking the recurrence of adenocarcinomas that arise within an RCH after surgical extirpation.⁸

Complete surgical resection of an RCH is necessary to prevent recurrence and the development of draining sinuses and to evaluate for malignant transformation. A combined anterior and posterior pelvic approach with complete resection of the tumor and adjacent involved structures is recommended for cysts with malignant transformation. The incidental finding of a retrorectal mass during laparotomy also necessitates resection and has been advocated by several authors.^5,6Local chemoradiotherapy is frequently recommended for an adenocarcinoma that arises within an RCH because of the frequently large size of these tumors, the difficulty in evaluating surgical margins, and the compression of adjacent structures. Follow-up with computed tomography or magnetic resonance imaging after treatment is recommended.

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Correspondence:Kevin G. Billingsley, MD, Department of Surgery, Oregon Health and Science University, 3181 SW Sam Jackson Park Rd, Mail Code L223A, Portland, OR 97239.

Accepted for Publication:December 21, 2006.

Author Contributions:Study concept and design: Mayo, Dobos, and Billingsley. Acquisition of data: Mayo and Huang. Analysis and interpretation of data: Mayo and Huang. Drafting of the manuscript: Mayo and Huang. Critical revision of the manuscript for important intellectual content: Mayo, Dobos, and Billingsley. Study supervision: Dobos and Billingsley. Histologic photographs, diagnosis, and interpretation: Huang.

Financial Disclosure:None reported.

Additional Contributions:Chris Corless, MD, PhD (Department of Pathology at Oregon Health and Science University), provided expertise in the pathologic analysis of the specimen.