Pseudosarcomatous myofibroblastic proliferation

by Jason Wasserman MD PhD FRCPC and Trevor Flood MD FRCPC
September 13, 2023

What is a pseudosarcomatous myofibroblastic proliferation?

A pseudosarcomatous myofibroblastic proliferation (PSMP) is a noncancerous growth that typically develops after surgical manipulation. Other names for this condition include pseudosarcomatous myofibroblastic neoplasm and postoperative spindle cell nodule.

Where are pseudosarcomatous myofibroblastic proliferations found?

Most PSMPs are found in the urinary tract, specifically the bladder and the prostate gland. However, PSMPs can also be found in the cervix, uterus, and skin.

Can the cells in a pseudosarcomatous myofibroblastic proliferation spread to other parts of the body?

No. A PSMP is a noncancerous growth and the cells will not metastasize (spread) to other parts of the body.

What causes a pseudosarcomatous myofibroblastic proliferation?

The most common cause of PSMP is prior surgical manipulation. For example, PSMP in the urinary tract commonly develops after a procedure called a transurethral resection of a bladder tumour (TURBT) is performed. PSMP in the cervix or uterus may develop after a loop electrosurgical excision procedure (LEEP) or curettage is performed.

What are the symptoms of pseudosarcomatous myofibroblastic proliferation?

Most PSMPs do not cause any symptoms and the growth is discovered incidentally, for example,  when an examination of the bladder or prostate gland is performed. Large nodules may cause symptoms such as bloody urine and difficulty initiating urination or fully emptying the bladder.

How is this diagnosis made?

This diagnosis can be made after the growth is removed and the tissue is examined under the microscope by a pathologist.

What does a pseudosarcomatous myofibroblastic proliferation look like under the microscope?

When examined under the microscope, a PSMP is made up of spindle-shaped cells called fibroblasts or myofibroblasts. The spindle cells are arranged in intersecting bundles described as fascicles or fascicular. Mitotic figures (cells dividing to create new cells) may be seen although no atypical mitotic figures should be identified. A type of injury called an ulcer may be seen at the surface of the tissue and a combination of acute and chronic inflammatory cells are usually associated with the ulcer. Small blood vessels may be seen in the connective tissue surrounding the spindle cells.

What other tests may be performed to confirm the diagnosis?

Pathologists often perform a test called immunohistochemistry (IHC) to confirm the diagnosis. This test helps distinguish a PSMP from other types of growths that can look similar under the microscope. When IHC is performed, the spindle cells are typically positive for muscle markers such as smooth muscle antigen (SMA) and desmin. The spindle cells may also be positive for ALK protein.