Fibroblastic polyp of the colon / colonic perineuroma

Definition

A mesenchymal polyp of the colorectum comprising a monomorphic spindle cell proliferation separating entrapped colonic crypts. It is argued that fibroblastic polyp and perineuroma of the colon are the same entity5.

Epidemiology

Fibroblastic polyps constitute about 0.2% of all colonic polyps1. They are found across a wide adult age range.

Clinical features

Radiology

Macroscopic appearances

These polyps are up to 1.5 cm in diameter and solitary, but there are frequently associated hyperplastic polyps1.

Histopathology

The lesion is circumscribed but unencapsulated. The lamina propria is expanded by a monomorphic spindle cell proliferation. The spindle cells have pale cytoplasm and oval or tapered nuclei. The spindle cell proliferation widely separates colonic crypts. Cytological pleomorphism, necrosis and mitotic activity are absent. 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

	Fibroblastic polyp	Perineuroma
Vimentin	14/141, 8/84
Fascin	4/43
CD34	2/14(weak focal staining)1, 2/43	2/102
SMA	2/14(weak focal staining)1, 0/84	0/102
S-100	0/141, 0/84	0/102
CD21	0/43
CD23	0/43
CD31	0/141
CD34	0/84
CD35	0/43
CD117	0/14(mast cells are positive)1, 0/84	0/102
EMA	0/141, 0/43, 0/84	9/102
AE1/AE3	0/84
MNF116		0/102
bcl-2	0/141
Desmin	0/141, 0/84	0/102
Caldesmon	0/84	0/102
Calponin	1/43
Claudin-1		4/102
GFAP		0/102
Neurofilament		0/102
Cyclin D1	0/43
PG-M1	0/84
CDX-2	0/84
Factor XIIIa	0/84
Ki-67	~1%4

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.
Solitary fibrous tumour: positive for CD34 and bcl-2.
Nerve sheath tumours & neuroma: S-100 positive
Ganglioneuroma
perineuroma: EMA positive
Schwannoma
Mucosal neuroma: positive for S-100.

Prognosis

These tumours do not recur after resection.

References

1 Eslami-Varzaneh F, Washington K, Robert ME, et al. Benign fibroblastic polyps of the colon: a histologic, immunohistochemical, and ultrastructural study. Am J Surg Pathol 2004; 28:374-8

2 Hornick JL, Fletcher CD. Intestinal perineuriomas: clinicopathologic definition of a new anatomic subset in a series of 10 cases. Am J Surg Pathol 2005; 29:859-65

3 Zamecnik M, Chlumska A. Fibroblastic polyp of the colon shares features with Vanek tumor. Am J Surg Pathol 2004; 28:1397-8; author reply 1398.

4 Groisman GM, Polak-Charcon S, Appelman HD. Fibroblastic polyp of the colon: clinicopathological analysis of 10 cases with emphasis on its common association with serrated crypts. Histopathology 2006; 48:431-7

5 Groisman GM, Polak-Charcon S. Fibroblastic polyp of the colon and colonic perineurioma: 2 names for a single entity? Am J Surg Pathol 2008; 32:1088-94