Bladder and Urethral Neoplasia: What's New?

Introduction
In dogs, the most common site for neoplasia in the urinary tract is the bladder although it comprises less 1% of all canine tumours.

Aged female animals (mean 10 years) are usually affected with the exception of embryonal rhabdomyosarcoma that occurs mainly in young dogs and particularly those of large breeds.

Bladder cancer is much rarer in the cat than in the dog, accounting for less than 0.5% of all tumours.

The majority of tumours in both the dog (97% of cases) and cat (80% of cases) are epithelial, the most common being transitional cell carcinoma and they may be solitary or multiple and can appear as papillary or non- papillary mass, with an infiltrating or non-infiltrating growth.

Tumours most commonly arise at the trigonal region of the bladder.

Transitional cell carcinoma is usually locally invasive and, infiltrating through the bladder wall, it can extend into adjacent tissues and regional organs such as the pelvic fat, prostate or uterus, vagina or rectum. Peritoneal seeding may also occur as well as metastatic spread to internal iliac and lumbar lymph nodes, lungs, liver, spleen and pelvic bones. Nearly 50% of the cases had regional lymph node involvement at time of diagnosis.

Mesenchymal bladder tumours are mainly derived from fibrous tissue or smooth muscle and these include leiomyoma, haemangioma and fibroma along with their malignant counterparts. Rhabdomyosarcoma (botryoid or embryonal sarcoma) is a rare embryonal myoblast tumour which sometimes occurs in the bladder wall. It usually arises in the trigonal region, is often multi-lobulated and may occlude the ureteric orifices. While most mesenchymal bladder tumours are locally invasive and less likely to metastasise than transitional cell carcinoma, however, embryonal rhabdomyosarcoma has a tendency for both local recurrence after surgery and distant metastasis. Lymphoma has also been reported.  [...]