- Rare, but considered the most common benign mesenchymal tumor in the bladder.
- More common in female, may present with obstructive symptoms.
- Gross: well-circumscribed submucosal mass (< 2 cm) with firm gray-white trabeculated cut surface; rare cases of up to 25 cm in size (image A).
- Fascicles of spindle cells with cigar-shaped nuclei (image B).
- No mitoses or necrosis.
- Excellent prognosis.
- Rare, but is the most common type of sarcoma that arises in the bladder.
- More common in male.
- Gross: lobulated gray-tan mass (mean 7 cm) often with necrosis, with or without ulceration of the overlying mucosa.
- DDX: sarcomatoid carcinoma and myofibroblastic tumor, which both similar to LMS express smooth muscle actin (traditionally a smooth muscle tumor marker) and pankeratin (traditionally an epithelial marker) (beware of these overlap).