Benign and Malignant Bladder Lesions

Leiomyoma

Leiomyoma is the most common benign mesenchymal tumor of the bladder, accounting for 0.4% of all bladder tumors. Most leiomyomas occur in middle-aged women, with 76% of patients with leiomyoma being female.

Hemangioma

Bladder hemangioma, accounting for 0.3% of all bladder tumors, is typically a congenital tumor that is usually noted during childhood or adolescence but may be diagnosed at a later age as well. There may be a slight male predominance. It is most commonly observed as a single lesion, although additional hemangiomas may be observed elsewhere in the body up to 30% of the time, for example, in the skin. These tumors may occur in association with Klippel-Trenaunay-Weber and Sturge-Weber syndromes.

Paraganglioma

Paraganglioma, a pheochromocytoma occurring outside the adrenal gland, is uncommon, accounting for 0.1% of all bladder tumors. Although it may occur at any age, paraganglioma is more common among adults. There is a slight female predilection. Whereas most paragangliomas are isolated, they also may occur in conjunction with phakomatoses such as neurofibromatosis, Sturge-Weber syndrome, and tuberous sclerosis or other syndromes, including von Hippel-Lindau syndrome or multiple endocrine neoplasia types 2a and 2b. Rare observations of familial extra-adrenal pheochromocytomas also have been reported. In 5% to 15% of cases, paraganglioma of the bladder may be malignant.

Neurofibroma

Neurofibroma is a rare bladder tumor, although the urinary bladder is the most common site of involvement within the genitourinary system. These tumors occur in isolation or in association with neurofibromatosis type 1 (NF1) in 55% of cases. Neurofibromas are more common in men 20 to 40 years of age. A younger age at onset suggests association with NF1. Neurofibromas associated with NF1 are usually multiple or are of the pathognomonic plexiform type. Malignant degeneration of neurofibromas, more common in cases associated with NF1, should be suspected in tumors that rapidly increase in size or are heterogeneous in appearance.

Inflammatory Pseudotumor

Inflammatory pseudotumor is also known by its more descriptive name, pseudosarcomatous fibromyxoid tumor, which better reflects its histologic composition. This is a rare tumor that occurs at any age from childhood to late adulthood and may have a slight male predilection. First described in the lung, inflammatory pseudotumor may involve any organ. The tumor behaves aggressively and mimics malignancy on imaging. Distinction is made only by histologic examination.

Solitary Fibrous Tumor

Solitary fibrous tumor is an exceedingly rare tumor in the urinary bladder with only seven reported cases in the literature. It is most commonly seen in the thoracic cavity, where it involves the visceral pleura. Reports of extrapleural involvement in multiple other organ systems also exist. It preferentially affects men 42 to 67 years of age.

Lipoma and Fibroma

Lipoma and fibroma occur only rarely in the urinary bladder and demonstrate features in the urinary bladder similar to those seen in other more commonly involved sites in the body.

Leiomyoma

Leiomyoma is usually a solitary tumor that exhibits growth intraluminally (63%), intramurally (7%), or outside the confines of the bladder (30%). The lesion typically occurs at the bladder base near the trigone, although it also may be found on the lateral or posterior walls.

Hemangioma

Hemangioma manifests as a small, lobulated, broad-based, sessile mass in the bladder dome or posterolateral wall. Although most hemangiomas extend into the muscular layer of the bladder wall, approximately one third are located in the sub­mucosa and a minority may also extend beyond the bladder wall. Hemangiomas also may manifest as diffuse bladder wall thickening.

The three distinct types of hemangiomas described include cavernous, capillary, and arteriovenous. The cavernous type accounts for most (78%) bladder hemangiomas, whereas capillary and arteriovenous types each represent 10% of cases.

Paraganglioma

Paragangliomas arise from the chromaffin cells of the sympathetic plexus in the bladder wall. Most are found near the trigone, although they may occur anywhere in the bladder.

Neurofibroma

Neurofibromas originate from the sheath of nerve plexuses entering near the bladder trigone. The tumor manifests as a smooth, well-defined focal intraluminal or intramural mass anywhere in the bladder. The plexiform variety manifests as a focal, nodular mass resulting in bladder wall thickening or as diffuse bladder wall thickening that involves only the inner wall, sparing the outer bladder wall. Plexiform neurofibromas also may involve surrounding structures such as the rectum, urethra, prostate, seminal vesicles, uterus, vagina, and the pelvic sidewalls.

Inflammatory Pseudotumor

The pathogenesis of this tumor is uncertain, although it is postulated to develop as a result of recurrent cystitis, inflammation, or prior surgery. However, many patients give no such prior history. This tumor usually occurs as a solitary mass ranging from 2 to 8 cm anywhere in the bladder with a tendency to spare the trigone. The solitary mass may project into the lumen, may be intramural, or may demonstrate extension into the surrounding extravesical tissues.

Solitary Fibrous Tumor

Solitary fibrous tumor may be an incidental finding or it may produce symptoms owing to its large size, which ranges from 3 to 17 cm. It may occur anywhere in the bladder.

The histopathologic features of solitary fibrous tumor may be confused with those of other tumors such as hemangiopericytoma, leiomyoma, leiomyosarcoma, and schwannoma. However, immunohistochemical analysis specifies the diagnosis because a solitary fibrous tumor strongly expresses CD34 on its surface that is not expressed as exuberantly by other tumors. Recently, this tumor has also shown positivity to BCL2, insulin-like growth factor type 2, and CD99.