Benign fibroblastic polyps of the colon

Definition

Mucosal polyps composed of benign spindle cells in the lamina propria with features of fibroblastic differentiation.

Epidemiology

Benign fibroblastic polyps constitute about 0.2% of all colonic polyps. They occur in adults.

Macroscopic appearances

These polyps are up to 1.5 cm in diameter. They are solitary.

Histopathology

The lamina propria is expanded by a uniform population of spindle cells, separating the crypts. The margins are pushing. The spindle cells have pale cytoplasm and blunt oval or tapering nuclei, without atypia. Stellate and giant cells are not a feature. There is no necrosis. Mitotic figures are not seen. Mast cells are abundant. The overlying epithelium is intact.

Immunohistochemistry

	Vimentin	strongly positive
	CD34	focal and weak positivity (abundant small calibre blood vessels positive)
	SMA	focal and weak positivity in 2/14 cases (muscularis mucosae may show a few fibres superficial to the tumour)
	S-100	negative
	CD117	negative (mast cells positive)
	EMA	negative
	CD31	negative (abundant small calibre blood vessels positive)
	bcl-2	negative
	Desmin	negative (muscularis mucosae may show a few fibres superficial to the tumour)

Ultrastructure

The spindle cells are surrounded by collagen. They shows features of fibroblasts: sparse organelles, abundant intermediate filaments, a lack of basal lamina, dense bodies or pinocytotic vesicles.

Differential diagnosis

• Inflammatory fibroid polyps: an oedematous stroma contains inflammatory cells, including numerous eosinophils. Characteristically, there are concentric fibroblasts around blood vessels. The stromal cells are positive for CD34 but negative for CD117. Benign fibroblastic polyps possibly represent an early stage of formation of inflammatory fibroid polyps.

• Gastrointestinal stromal tumour: CD117 positive.

• Smooth muscle tumours: strongly SMA and desmin positive.

• Nerve sheath tumours & neuroma: S-100 positive

• Ganglioneuroma

• perineuroma: EMA positive

• Solitary fibrous tumour: positive for CD34 and bcl-2.

Prognosis

These tumours do not recur after resection.

References

Eslami-Varzaneh, F., K. Washington, et al. (2004). "Benign fibroblastic polyps of the colon: a histologic, immunohistochemical, and ultrastructural study." Am J Surg Pathol 28(3): 374-8.

This page last revised 25.3.2004.

©SMUHT/PW Bishop