Leiomyomas are benign smooth muscle tumors. They are commonly found as uterine fibroids but occur rarely in the GI tract, arising from any smooth muscle. The stomach and small bowel are more common sites than the rectum and anus.1 Rectal lesions grow intraluminally and involve the rectal wall. Anal lesions arise from the internal anal sphincter and grow away from the anal canal.2
The tumors show female predisposition and present as firm perineal swellings around perimenopausal age.3 Workup is as for any unknown anal mass. MRI will demonstrate homogeneous, hypointense T1 and mixed T2 signals. The anatomical relations should be defined by examination under anesthesia and colonoscopy. The biopsy method is determined by location: endoscopic, operative, or radiological, with pathology showing benign spindle cells, positive for smooth muscle actin, desmin, caldesmon, estrogen, and progesterone receptors.4
Although these are benign lesions, they are usually treated by resection because of the potential for worsening symptoms and increasing size. Preoperative continence should be carefully evaluated and manometry considered. Lesions in the rectum usually involve the rectal wall and require at least partial rectal resection. Those in the anus can be resected with a perineal approach, as shown in this vignette. Recurrence rates are determined by anatomical location and completeness of excision.5 Preparation for surgery includes bowel cleansing and consent for anorectal resection and ostomy.
In prone and split leg positions, a curvilinear incision outside the anal margin allows access to the extrasphincteric space. The inflammatory pseudocapsule and smooth surface aid excision. Attention should be paid to preserving external sphincter fibers which adhere to the tumor. The origin of the tumor in the internal sphincter may be small, so identification and complete excision are important. Defects in the internal and external sphincter should be repaired and the lumen thoroughly examined for injury after excision. See Video Vignette.
Footnotes
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REFERENCES
- 1.Campos FG, Leite AF, Araújo SE, et al. Anorectal leiomyomas: report of two cases with different anatomical patterns and literature review. Rev Hosp Clin Fac Med Sao Paulo. 2004;59:296–301. [DOI] [PubMed] [Google Scholar]
- 2.Vorobyov GI, Odaryuk TS, Kapuller LL, Shelygin YA, Kornyak BS. Surgical treatment of benign, myomatous rectal tumors. Dis Colon Rectum. 1992;35:328–331. [DOI] [PubMed] [Google Scholar]
- 3.Miettinen M, Sobin LH, Sarlomo-Rikala M. Immunohistochemical spectrum of GISTs at different sites and their differential diagnosis with a reference to CD117 (KIT). Mod Pathol. 2000;13:1134–1142. [DOI] [PubMed] [Google Scholar]
- 4.Dasari BVM, Khosraviani K, Irwin TS, Scott M. Perianal leiomyoma involving the anal sphincter. Ulster Med J. 2007;76:173–174. [PMC free article] [PubMed] [Google Scholar]
- 5.Sturiale A, Fabiani B, Naldini G. A rare case of leiomyoma of the internal anal sphincter. Int J Surg Case Rep. 2016;23:4–7. [DOI] [PMC free article] [PubMed] [Google Scholar]