Pseudosarcomatous myofibroblastic proliferation

by Jason Wasserman MD PhD FRCPC and Trevor Flood MD FRCPC
June 12, 2025

A pseudosarcomatous myofibroblastic proliferation is a non-cancerous growth that can develop after certain surgical procedures or manipulations. Although it may sometimes be mistaken for cancer under a microscope, this condition is entirely benign (non-cancerous). Other names for this condition include postoperative spindle cell nodule and pseudosarcomatous myofibroblastic neoplasm.

Where are pseudosarcomatous myofibroblastic proliferations typically found?

Pseudosarcomatous myofibroblastic proliferations most commonly occur in the urinary tract, particularly in the bladder and prostate gland. However, these growths can also develop in other locations, such as the cervix, uterus, and occasionally on the skin.

What causes pseudosarcomatous myofibroblastic proliferations?

Pseudosarcomatous myofibroblastic proliferations develop as a reaction to surgical procedures or physical manipulation of tissues. For instance, in the urinary tract, this growth commonly forms following a procedure known as a transurethral resection of a bladder tumour (TURBT). Similarly, procedures performed on the cervix or uterus, such as a loop electrosurgical excision procedure (LEEP) or a curettage, can lead to the formation of these proliferations. Essentially, the body responds to surgical injury or irritation by producing these non-cancerous growths as part of the healing process.

What are the symptoms of a pseudosarcomatous myofibroblastic proliferation?

Most people with pseudosarcomatous myofibroblastic proliferations do not experience noticeable symptoms. Often, the proliferation is discovered incidentally during a routine medical exam or follow-up procedure.

However, if the proliferation grows larger, it may cause symptoms such as:

• Blood in the urine (hematuria).

• Difficulty initiating urination.

• Trouble completely emptying the bladder.

These symptoms typically occur if the growth becomes large enough to interfere with normal bladder function.

How is pseudosarcomatous myofibroblastic proliferation diagnosed?

A definitive diagnosis of a pseudosarcomatous myofibroblastic proliferation is made by a pathologist who examines the removed tissue under a microscope. Usually, this happens after the growth is surgically removed or biopsied. Pathologists perform careful microscopic evaluations to ensure the growth is accurately identified and distinguished from other potentially harmful conditions.

Microscopic features of pseudosarcomatous myofibroblastic proliferation

When viewed under the microscope, a pseudosarcomatous myofibroblastic proliferation has several distinctive features:

• Spindle cells: The growth is composed mainly of elongated cells known as spindle cells. These cells are longer than they are wide, resembling a spindle shape.

• Fascicles: The spindle cells often arrange themselves into intersecting bundles, known as fascicles, giving the tissue a characteristic appearance.

• Mitotic figures: Cells that are actively dividing (mitotic figures) might be visible, reflecting normal cell turnover due to healing and regeneration. Importantly, pathologists should not see any abnormal or atypical mitotic figures.

• Ulceration and inflammation: An injury known as an ulcer may be present on the tissue’s surface. Ulcers typically occur in conjunction with inflammation, featuring both acute (recent) and chronic (long-term) inflammatory cells.

• Blood vessels: Small blood vessels often appear within the connective tissue surrounding the spindle cells, reflecting increased blood supply to support healing.

What other tests may be performed to confirm this diagnosis?

To confirm the diagnosis, pathologists frequently perform an additional specialized test called immunohistochemistry (IHC). This test utilizes specific antibodies to identify particular proteins in cells, enabling the clear differentiation of pseudosarcomatous myofibroblastic proliferations from other similar-looking conditions.

When immunohistochemistry is performed on a pseudosarcomatous myofibroblastic proliferation, the spindle cells typically test positive for markers associated with muscle tissue, including smooth muscle actin (SMA) and desmin.

Additionally, spindle cells sometimes express a protein known as ALK (anaplastic lymphoma kinase). These results enable pathologists to confidently establish the diagnosis of pseudosarcomatous myofibroblastic proliferation and rule out conditions that could mimic its appearance, such as certain types of cancer.

How is a pseudosarcomatous myofibroblastic proliferation treated?

In most cases, no further treatment beyond removing the irritating factor is necessary. If symptoms occur or the growth interferes with organ function, your doctor may recommend surgical removal of the nodule. Since these nodules are benign, they do not require chemotherapy or radiation therapy. Following removal, pseudosarcomatous myofibroblastic proliferations typically do not recur, especially once the source of irritation has been addressed.

Follow-up care

Your doctor may recommend regular follow-up visits, especially if you have ongoing symptoms or are at risk of repeated irritation to the affected area. Follow-up care can help ensure proper healing and monitor for any recurrence or complications.

Questions to ask your doctor

• What specifically caused my pseudosarcomatous myofibroblastic proliferation?

• Will I require treatment for this growth, or will it resolve on its own?

• Could this growth recur after removal?

• What symptoms should I look out for that might indicate a recurrence or complication?

• Should I schedule regular follow-up appointments or imaging tests?

• Are there steps I can take to reduce the risk of developing this condition again?