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Skin - Fibroadnexal Hamartoma

Image of fibroadnexal hamartoma in the skin from a female F344/N rat in a chronic study
Fibroadnexal hamartoma-exophytic growth composed of dilated hair follicles and overlying hyperplastic epithelium in a female F344/N rat from a chronic study.
Figure 1 of 6
Image of fibroadnexal hamartoma in the skin from a female F344/N rat in a chronic study
Fibroadnexal hamartoma-exophytic growth composed of dilated hair follicles and overlying hyperplastic epithelium in a female F344/N rat from a chronic study.
Figure 2 of 6
Image of fibroadnexal hamartoma in the skin from a female F344/N rat in a chronic study
Fibroadnexal hamartoma-exophytic growth composed of dilated hair follicles and overlying hyperplastic epithelium in a female F344/N rat from a chronic study.
Figure 3 of 6
Image of fibroadnexal hamartoma in the skin from a male F344/N rat in a chronic study
Fibroadnexal hamartoma-flat lesion composed of fibrous connective tissue and dilated follicles lined by flattened epithelium in a male F344/N rat from a chronic study.
Figure 4 of 6
Image of fibroadnexal hamartoma in the skin from a male F344/N rat in a chronic study
Fibroadnexal hamartoma-flat lesion composed of fibrous connective tissue and dilated follicles lined by flattened epithelium in a male F344/N rat from a chronic study.
Figure 5 of 6
Image of fibroadnexal hamartoma in the skin from a male F344/N rat in a chronic study
Fibroadnexal hamartoma-flat lesion composed of fibrous connective tissue and dilated follicles lined by flattened epithelium in a male F344/N rat from a chronic study.
Figure 6 of 6
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comment:

Fibroadnexal hamartomas are uncommon spontaneous lesions. They consist of one or more pilosebaceous units in which the hair follicle is usually dilated and may be surrounded by abundant fibrous connective tissue ( Figure 4image opens in a pop-up window , Figure 5image opens in a pop-up window , and Figure 6image opens in a pop-up window ). The epithelium of the hair follicle may be flattened ( Figure 5image opens in a pop-up window and Figure 6image opens in a pop-up window ), or it may be slightly hyperplastic with projections into the surrounding connective tissue ( Figure 3image opens in a pop-up window ). Multiple sebaceous glands are often associated with a single follicle. The overlying epidermis is often hyperplastic and hyperkeratotic. The lesions may be exophytic ( Figure 1image opens in a pop-up window , Figure 2image opens in a pop-up window , and Figure 3image opens in a pop-up window ) or flat ( Figure 4image opens in a pop-up window , Figure 5image opens in a pop-up window , and Figure 6image opens in a pop-up window ).

The pathogenesis of these lesions is unknown. They are dysplastic lesions but are not likely to be preneoplastic. It is unknown if they develop as an abnormal healing response at sites of trauma or if they are congenital. Of 6 hamartomas identified in the NTP database, 4 have been seen in rats and 2 in mice. One occurred in a female rat; all others occurred in males.

recommendation:

These lesions are occasionally observed grossly at necropsy and require a correlating histologic diagnosis. Therefore, they should be diagnosed whenever present but should not be assigned a severity grade.

references:

None available.
NTP is located at the National Institute of Environmental Health Sciences, part of the National Institutes of Health.