Lipomas are the most common (50%) soft-tissue tumors¹. Progression to liposarcoma is rare². Depending on their size, they may cause compression and displacement of adjacent structures producing different symptoms¹.

We chose this case because it is clinically exceptional. A 49-year-old female patient with a history of depression well-controlled with drug therapy attended a scheduled visit due to severe anal pain (9/10 on the VAS scale) associated with defecation urgency, tenesmus, dyspareunia and moderate/severe gas and fecal incontinence (Wexner score = 143) over the past months, with significant impact on her quality of life. On examination, an elastic soft tumor was observed at the level of the right buttock suggestive of lipoma about 3 centimeters distant from the anal verge. There were also skin stigmata of a previous infection already resolved. The tumor did not seem to be attached to the deep planes. On rectal examination, the sphincter was slightly hypotonic, and a frank, non-obstructive extrinsic compression was found at about 3 cm from the external anal verge (EAV), causing lateral bulging.

The ultrasound scan showed hyperechoic subcutaneous tissue with diffuse enlargement and mass effect. A magnetic resonance imaging scan was ordered. An encapsulated, non-lobulated mass with a size of 15.7 × 9 × 6 cm was identified in the right buttock, extending from the subcutaneous tissue to the deep planes through the ischioanal fossa and ischiorectal fossa, displacing the levator ani muscle and rectum (Fig. 1). The mass had the characteristics of adipose tissue, was close to the EAV and affected the nerves of the sacral plexus. Considering its large size, a malignant mesenchymal tumor could not be ruled out, and core needle biopsy (CNB) of the mass was performed under ultrasound guidance. The histologic examination showed mature adipose tissue.

Figure 1 Magnetic resonance imaging showing the large lipoma (black arrow) displacing the rectum and the levator ani muscle (white arrow) 

Elective surgery was indicated under general anesthesia, with the patient in the prone position (jackknife position). An elliptical incision was made in the ischiorectal fossa, revealing a large encapsulated lipomatous tumor with well-defined planes, in contact with the rectal wall but without infiltrating it, with upward displacement of the levator ani muscle. The lesion was excised en bloc. Operative time was 1 hour. The postoperative period was uneventful and the patient was discharged 48 hours after the procedure.

The pathological diagnosis was encapsulated mature lipoma with a size of 20 × 13 × 6 cm (Fig. 2). Further cytogenetic testing was necessary to rule out malignancy due to the tumor size. MDM2 gene amplification (12q15) by FISH on interphase nuclei4 was performed using Vysis MDM2/CEP 12 probe, with negative results.

Figure 2 Surgical resection specimen of lipoma 

One month later the wound had healed and she was free of symptoms. She remained asymptomatic during the 6-month follow-up.

We performed a literature search in PubMed, updated on December 16, 2020, using the following strategy: (Lipoma) AND [(Fecal incontinence) OR (Incontinence, Fecal) OR (Incontinences, fecal) OR (anorectal)] to assess the association between ischiorectal lipoma and the presence of anorectal symptoms.

A total of 87 articles were retrieved, but none of them could establish any association between anorectal lipoma and perineal symptoms.

These articles mainly deal with the relationship between perineal lipomas and congenital defects, most of them diagnosed during intrauterine life or in the first days of life, with no reference to their diagnoses in adults without associated malformations. The only case reports with anorectal symptoms in an adult patient were published by Bradley D. Shepherd et al.⁵. Yet, both lipomas were not located in the perianal region but were anterior to the sacrum, so they cannot be considered similar to our case because of their location and surgical approach (they were resected through midline laparotomy).

Based on the systematic review of the literature, we can ensure that the present case is exceptional. This benign condition results in significant anatomical abnormalities (compression and displacement of the rectum and levator ani muscle, and possible involvement of the presacral plexus due to its proximity) producing significant impairment in the patient’s quality of life (anal pain, defecation urgency, gas and fecal incontinence, tenesmus and dyspareunia).

The diagnosis is mainly clinical and radiological; the best results were obtained with MRI of the pelvis, computed tomography (CT) scan, endoscopic ultrasound or a combination of the three tests⁵.

Surgical treatment is indicated with complete excision of the lesion. Given the large size of these lesions, it is necessary to perform cytogenetic analysis to exclude MDM2 gene amplifications to rule out potentially malignant mesenchymal lesions⁴. The surgical results at 6 months are favorable with complete absence of symptoms.