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An Unusual Presentation of Rectal Leiomyoma

June 5, 2008

By Edwards, Michael A Beatty, John S; Shah, Malay B; Bittner, James G IV

To the Editor: Non-epithelial mesenchymal tumors, including gastrointestinal stromal tumors (GISTs) and smooth muscle tumors (SMTs), are rare and may occur in any part of the alimentary tract.1 GISTs originate from the interstitial cell of Cajal, an intestinal pacemaker cell, and represent 1 per cent to 3 per cent of all gastrointestinal malignant tumors. Approximately 5 per cent of GISTs occur in the colon and rectum overall, with 8 per cent of those appearing in the distal rectum.2

Immunophenotyping now allows for differentiation between GIST and SMT. GISTs have an activating mutation in KIT (CD117), a receptor tyrosine kinase encoded from the c-kit proto-oncogene. This mutation leads to ligand-independent activation and signal transduction mediated by activated KIT.1,2 SMTs originate from the muscularis propria and are differentiated from GISTs by immunophenotype staining positive for vimentin, desmin, and smooth muscle actin (SMA), and staining negative for KIT (CD117) and CD34.1

Rectal leiomyoma accounts for only 5 per cent to 10 per cent of all gastrointestinal SMTs and 0.07 per cent to 0.1 per cent of malignant SMTs (leiomyosarcoma).1 Most patients with gastrointestinal leiomyoma are diagnosed between the fifth and sixth decades of life, with few cases reported in young individuals. A significant number of SMTs are less than 1 cm at diagnosis, usually found incidentally during screening endoscopy and removed by snare polypectomy. Larger, more aggressive tumors necessitate surgical resection.1-4

A 19-year-old white male presented with a 4-week history of blood per rectum, weakness, and vague abdominal pain. Colonoscopy revealed a rectal mass measuring 3 cm in diameter approximately 8 cm from the anal verge, and biopsy demonstrated normal colon mucosa with reactive mucosal changes, granulation tissue, and no evidence of malignancy. Subsequent computed tomography of the abdomen and pelvis exposed an intraluminal rectal mass (3.7 cm x 4.4 cm) limited to the submucosa with no evidence of extraluminal extension, lymphadenopathy, or metastases (Fig. 1). The patient underwent rigid proctosigmoidoscopy, revealing a 5 cm rectal mass with the most proximal portion located 10 cm from the anal verge. A transanal incisional biopsy and frozen section confirmed the presence of spindle cells with benign features. Transanal excision of a circumscribed lesion measuring 5.5 cm x 3.9 cm x 3.5 cm was performed. Completion of a flexible sigmoidoscopy revealed a patent rectum and intact mucosal repair. Final pathological examination of the excised tumor proved interlacing bundles of smooth muscle cells and multinucleated cells plus immunophenotyping consistent with leiomyoma.

FIG. 1. Computed tomography of the pelvis demonstrating a circumscribed rectal mass (arrow).

Smooth muscle tumors originate from the muscularis propria of the intestinal wall. Spindle cell tumors of the gastrointestinal tract are mesenchymal proliferations derived from smooth muscle cells or from gastrointestinal pacemaker cells. Immunohistochemistry now allows differentiation between smooth muscle and gastrointestinal stromal tumors. GISTs are CD117 positive and can be CD34 (70%), S100 protein (

The true incidence of rectal leiomyoma remains uncertain. Studies before the routine use of immunophenotyping estimated the incidence to be 0.1 per cent to 3 per cent.2 Most patients present in the fifth and sixth decades of life. As such, the finding of a rectal leiomyoma in a 19-year-old male is unusual. Differentiation between benign (leiomyoma) and malignant (leiomyosarcoma) SMTs can be difficult. Certain tumor characteristics are suggestive of malignancy, including tumor size greater than 5 cm, tumor cell necrosis, ulceration, cellular atypia, and the presence of three or more mitotic figures/10 high-powered fields.1,2 Transrectal ultrasound (TRUS) may also help in differentiating benign and malignant disease, the latter presenting with disruption of normal tissue planes, cystic degeneration, and lymphadenopathy on ultrasonography.3 Although the patient in this account did not undergo TRUS, the radiographic finding of a tumor size greater than 5 cm heightened the preoperative risk for malignant degeneration.

There are no defined treatment algorithms for SMTs. Although imatinib has shown promise in treating locally advanced and metastatic gastrointestinal stromal tumors (54% response rate), no radiochemotherapeutic options are presently available for SMTs, thus surgery remains the only method for cure.2 Obtaining adequate surgical margins is essential regardless of potential risk for malignancy because cases of metastases after resection of benign SMTs have been reported. Therefore, surgical options are dictated primarily by tumor location and extent.

Surgical options for rectal SMTs include transanal excision, transanal endoscopie microsurgery, low anterior resection, or abdominoperineal resection. An optimal selection of surgical procedure depends on tumor location, size, and ability to obtain tumor-free margins.4 In this case, proctosigmoidoscopy revealed a tumor that was larger and located more proximally than reported by flexible endoscopy. Therefore, intraoperative rigid proctosigmoidoscopy was recommended as it may permit more accurate determination of tumor size and location than flexible endoscopy in selected cases. Suspected benign middle and distal rectal lesions may be treated by transanal excision or transanal endoscopie microsurgery if adequate tumor margins can be achieved; otherwise, low anterior re section or abdominoperineal resection may be warranted.4 In this instance, a curative transanal excision was performed for a 5 cm lesion located 10 cm from the anal verge.

Local recurrence is not uncommon, even with benign lesions. Patients with benign disease may present with recurrence and malignant degeneration. For those who develop leiomyosarcoma, the 5- year mortality ranges from 15 per cent to 40 per cent.1 Recurrence may present late, so close follow-up is necessary for all patients with SMTs, both benign and malignant. CT imaging every 6 months for the first year and then annually for at least 5 years is recommended to monitor for locoregional and distant recurrence. Flexible gastrointestinal endoscopy and TRUS are also useful adjuncts for long-term follow-up.

The authors wish to acknowledge the Virtual Education and Surgical Simulation Laboratory as funded by the Department of Surgery, Medical College of Georgia.

REFERENCES

1. Bahadursingh AM, Vagefi PA, Howell A, et al. Spindle cell tumor of the distal rectum. Dig Dis Sei 2005;50:37^1.

2. Miettinen M, Furlong M, Sarlomo-Rikala M, et al. Gastrointestinal stromal tumors, intramural leiomyomas, and leiomyosarcomas in the rectum and anus: A clinicopathologic, immunohistochemical, and molecular genetic study of 144 cases. Am J Surg Pathol2001;25:l 121-33.

3. Hsieh JS, Huang CJ, Wang JY, Huang TJ. Benefits of endorectal ultrasound for management of smooth muscle tumor of the rectum: Report of three cases. Dis Colon Rectum 1999;42: 1085-8.

4. Zerilli M, Lotito S, Scarpini M, et al. Recurrent leiomyoma of the rectum treated by endoscopie transanal microsurgery. G Chir 1997; 18:433-6.

Presented at the Annual Scientific Meeting and Postgraduate Course Program, Southeastern Surgical Congress, Birmingham, AL, February 9-12, 2008.

Address correspondence and reprint requests to Michael A. Edwards, M.D., Assistant Professor of Surgery Director, Virtual Education and Surgical Simulation Laboratory, Department of Surgery, Medical College of Georgia School of Medicine, 1120 15th Street, Augusta, Georgia 30912. E-mail: miedwards@mcg.edu.

Michael A. Edwards, M.D.

John S. Beatty, M.D.

Malay B. Shah, M.D.

James G. Bittner IV, M.D.

Virtual Education and Surgical Simulation Laboratory

Department of Surgery

Medical College of Georgia School of Medicine

Augusta, Georgia

Copyright Southeastern Surgical Congress May 2008

(c) 2008 American Surgeon, The. Provided by ProQuest Information and Learning. All rights Reserved.




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