The most frequent benign mesenchymal tumor in the urinary bladder is leiomyoma. Bladder lipomas are rare tumors. As far as we are aware, only 15 cases of this neoplasm have been documented[2-16]. We report herein a small mucosal lipoma of the bladder incidentally discovered during cystoscopy. Besides, a review of the literature on this subject is presented.
Microscopic study demonstrated a well-circumscribed, ovoid, expansile nodule of mature adipose tissue located within the lamina propria of the mucosa layer without any evidence of malignancy or bladder wall invasion (Figure 2). The lesion was covered by a thin rim of urothelial mucosa (Figure 3). The maximum diameter of the fat lesion was 0.5 cm.
The patient had an uneventful recovery during the postoperative follow-up period.
Bladder lipoma is rare. A review of published cases of bladder lipoma, including the present report, yielded a total of 16 (Table I). The mean age of these patients at presentation was 56.2 years (SD, 12.4; range, 32-75 years). Nine (56.2%) patients were male. The lesion can show endophytic or exophytic, and sessile or pedunculated growth. All tumors had a yellowish color.
Table I: Bladder lipomas: Review of the literature
Most tumors were endophytic in mucosa or submucosa. Attenuation coefficient of these lesions in Hounsfield units indicates lipomatous tissue by CT. Cystoscopy findings were very suggestive. In these cases transurethral resection was performed to achieve histologic confirmation. These tumors were small and most of them (59.1%) measured less than 2 cm. Exophytic neoplasms can be very large[2,13] and they may present as a retroperitoneal mass[13]. Lipomas were located in every site of the bladder and most of them were covered by urothelial mucosa. Seven (36.8%) cases were located in the posterior wall and 5 (26.3%) in the fundus or dome. They may present with hematuria, urinary frequency, nocturia, urinary tract infection, or as a retroperitoneal mass. The most common presentation (56.2%) is asymptomatic gross or microscopic hematuria. The bleeding can be attributed to excoriations of the mucosa over the lipoma. The neoplasm was incidentally observed in 3 (18.7%) of cases. In 4 (25%) cases the patients had multiple lipomas.
Microscopically, lipomas were well-circumscribed, expansile neoplasms composed of mature adipose tissue. The voluminous tumor described by Sederl was a fibrolipoma[2].
Differential diagnosis of bladder lipoma includes welldifferentiated liposarcoma, pelvic lipomatosis, and urachal fibrolipoma. Well-differentiated liposarcoma shows marked variation in adipocyte size, nuclear hyperchromasia, scattered lipoblasts, and bizarre multinucleated stromal cells. Pelvic lipomatosis is characterized by massive overgrowth of mature adipose tissue in the perivesical and perirectal portions of the pelvic retroperitoneum. The fat tissue causes external compression of the lower urinary tract and rectosigmoid colon. The patients complain of perineal or lower abdominal pain, increased urinary frequency, hematuria and constipation. The fatty growth is diffuse rather than nodular[17]. The urachus, which extends from the umbilicus to the apex of the bladder, involutes shortly after birth becoming a fibrous cord called the median umbilical ligament. Though rarely, a calcified fibrolipoma may appear in this structure[18]. Bladder lipomas behaved as benign tumors with no recurrences.
In conclusion, lipoma is a rare finding within the bladder wall. The most common presentation is asymptomatic hematuria. The tumor may be incidentally found during the clinical search for another process. Most tumors were endophytic, yellowish, located in mucosa/submucosa, and measured less than 2 cm. CT density and cystoscopic observation suggest benign adipose tissue. All reported cases behaved as benign lesions and did not show recurrences.
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