follicular malformation (hamartoma) within a nevus

INTRADERMAL NEVUS (NEVOCELLULAR) THAT CONTAINS A FOLLICULAR MALFORMATION/HAMARTOMA

It is not uncommon for ordinary nevocellular nevi to contain malformed pilosebaceous units. The abnormalities are often subtle, consisting of abnormal placements and configurations of sebaceous units, hair bulbs, or other components of the unit. Unless one is particularly interested in the structure of pilosebaceous units, the abnormalities tend to go undetected. In this particular case, the abnormality is striking. Interconnecting strands of follicular epithelium are separated by stroma that varies from myxoid in the middle and deep part of the lesion to eosinophilic in the most superficial part of the lesion. The distinction between a malformation and a hamartoma is a matter of definition. It is convenient to think of a hamartoma as having more bulk than a malformation though each may be composed of the same subunits. Lesions such as this are on the borderline between the two possibilities.

It is of parenthetical interest that nevus sebaceous of Jadassohn may start out as a field containing malformed follicles and, at later dates, develop hamartomas and neoplasms. It is also of interest that desmoplastic trichoepitheliomas are occasionally found within nevi.

Scan power view showing a vertically oriented follicular malformation or hamartoma within an intradermal nevus.

High power view of the superficial part of the follicular lesion. Most of the stroma in the uppermost part is collagenous and eosinophilic. It appears to be an integral part of the lesion. Nevus cells are to the left of the follicular lesion. The epithelial cells in the interconnecting strands have a high nuclear/cytoplasmic ratio as in isthmic epithelium or epithelium of mantle structures. This area shares some of the features that can be seen in a fibrofolliculoma.

Low power view of the mid portion of the follicular lesion. The stroma between the interconnecting branches of epithelium is myxoid. Nevus cells are seen on each side of the follicular lesion. Once again, the stroma forms an integral part of the mass.

Medium power view of the deep part of the lesion. Nevus cells are on each side of the follicle. The follicle of origin extends into the base of the biopsy.

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	Scan power view showing a vertically oriented follicular malformation or hamartoma within an intradermal nevus.
	High power view of the superficial part of the follicular lesion. Most of the stroma in the uppermost part is collagenous and eosinophilic. It appears to be an integral part of the lesion. Nevus cells are to the left of the follicular lesion. The epithelial cells in the interconnecting strands have a high nuclear/cytoplasmic ratio as in isthmic epithelium or epithelium of mantle structures. This area shares some of the features that can be seen in a fibrofolliculoma.
	Low power view of the mid portion of the follicular lesion. The stroma between the interconnecting branches of epithelium is myxoid. Nevus cells are seen on each side of the follicular lesion. Once again, the stroma forms an integral part of the mass.
	Medium power view of the deep part of the lesion. Nevus cells are on each side of the follicle. The follicle of origin extends into the base of the biopsy.