Pseudosarcomatous myofibroblastic proliferation

by Jason Wasserman MD PhD FRCPC and Trevor Flood MD FRCPC
January 4, 2024


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.

This article will help you understand your diagnosis and pathology report.

Where are pseudosarcomatous myofibroblastic proliferations found?

Most pseudosarcomatous myofibroblastic proliferations 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.

What causes a pseudosarcomatous myofibroblastic proliferation?

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

What are the symptoms of pseudosarcomatous myofibroblastic proliferation?

Most pseudosarcomatous myofibroblastic proliferations 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 pseudosarcomatous myofibroblastic proliferation 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.

postoperative spindle cell nodule

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.

About this article

This article was written by doctors to help you read and understand your pathology report. Contact us if you have any questions about this article or your pathology report. Read this article for a more general introduction to the parts of a typical pathology report.

Other helpful resources

Atlas of Pathology
A+ A A-