Abstract Four cases of hair follicle nevi are described. Hair follicle nevus is an extremely rare bamartoma occurring on the face, which has had no clear histopathologic definition until now. A short review of the clinicopathologic features of this disease is presented. Tbe definition of bair follicle nevus is the crowding of many tiny mature follicles among the nevi made up of the hairs and hair follicles.' It is not easy to make a definite differential diagnosis between hair follicle nevus and other hair follicle tumors because of the lack of any definite histopathologic classification of hair follicle tumors. Furthermore, few cases written in English have been reported.^^'' We found two cases from Korean literature.'•'' We present four cases of hair follicle nevi and summarize the previously reported cases.

Figure 1. A pruritic 5 mm diameter erythematous papule on the right cheek (case 1). The dermis showed numerous small well-differentiated hair follicles connected with some sebaceous glands, many dilated blood vessels with some endothelial cell proliferation, and mild mononuclear cell infiltration (Fig. 3). The collagen bundles were narrow and parallel to the epidermis in the upper portion, concentrically arranged around bair follicles. There was no smooth muscle fiber in the dermis.

Case Report Case 1: A 4-year-old girl visited the Department of Dermatology, Yonsei University Wonju College of Medicine, with a papule on the right cheek for 6 months. The skin lesion was a 5 mm diameter erythematous papule with pruritus (Fig. 1). Histopathologically, the epidermis showed acanthosis with intraepidermal pustules or crusts not associated with spongiosis or acantholysis and had no atypical nuclei or pleomorphism. The dermis showed the crowding of many tiny mature hair follicles with thick fibrous root sheaths, some sebaceous glands connected with hair follicles, some smooth muscle bundles, collagen bundles without thickening or loosening, and chronic nonspecific inflammations composed of mild mononuclear cell infiltrations.

Case 3: A 37-year-old woman showed a pruritic plaque on the right nasolabial fold. The skin lesion observed since childhood had been an asymptomatic flesh papule until 1 month ago. Recently, the skin lesion had enlarged slowly and changed into a pruritic bluishly erythematous plaque.

Case 2: A 43-year-old woman with a 2-year-old growing papule on the nose visited our department. The skin lesion was an asymptomatic 5 mm diameter flesh papule {Fig. 2). Histopathologically, the epidermis did not show any abnormalities without orthokeratosis and rete ridge elongation.

From the Departments of Dermatology, Yonsei University Wonju College of Medicine, Wonju, and Yonsei University College of Medicine, Seoul, Korea. Address for correspondence: Seung Hun Lee, M.D., Department of Dermatology, Yonsei University, Wonju College of Medicine, 162 Ilsan-Dong, Wonju, Korea 220-701.

Figure 2. An asymptomatic S mm diameter flesh papule on the nose (case 2). 578

Hair Follicle Nevus Choi et al.

centrically arranged around hair follicles, and there was no inflammatory cell infiltration. We summarized the clinical findings of the cases previously reported and those of our cases in Table 1.



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In the literature,'"^ we could not find definite diagnostic criteria for hair follicle nevus and other hair follicle tumors. Kligman and Pinkus* classified the hair differentiated tumors into hair nevus, follicuioma, trichoepithelioma, and keratotic basal cell epithelioma in descending order of differentiation. Thereafter, Gray and Helwig' proposed that the term "trichofolliculoma" is more appropriate than follicuioma. In 1976, Headington'" described the trichofolliculoma, which included follicuioma and hair follicle nevus. They also labeled small congenital nodules on the head and neck, which are composed of numerous tightly packed but well-formed vellus follicles as congenital vellus hamartomas. In

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Figure 3. The dermis showed small well differentiated hair follicles, many dilated blood vessels with some endothelial cell proliferation, and mononuclear cell infiltration (case 2). (hematoxylin and eosin, original magnification x 100)



Figure 4. Many small well differentiated hair follicle with very thick fibrous root sheath, mature sebaceous glands, many striated muscle bundles, a few smooth muscle bundles, and many dilated blood vessels were showed in the dermis (case 4). (hematoxylin and eosin, original magnification x 40) Figure 5. Small well differentiated hair follicles with very thick fibrous root sheath (case 4). (hematoxylin and eosin, original magnification x 200)

Histopathologically, the epidermis showed compact hyperkeratosis, acanthosis with some thickening of granular layers, and some dyskeratotic cells. The separation of the dermo-epidermal junction and solar degenerative change, dilated capillaries with perivascular mononuclear cell infiltrations, and multiple small mature hair follicles were observed in the dermis. Some sebaceous glands were around some hair follicles, but there are no smooth muscle bundles. The collagen bundles were of normal patterns. Case 4: A 19-year-old male had a 7 mm diameter pedunculated flesh nodule on the left nostril since birth. The excised nodule showed mild hyperkeratosis and some follicular plugging in the epidermis. In the dermis, we observed many small well-differentiated hair follicles with very thick fibrous root sheath {Figs. 4 and 5), mature sebaceous glands {Fig. 6), many striated muscle bundles {Fig. 7), a few smooth muscle bundles {Fig. 8), and many dilated blood vessels including many RBCS and thromboses. The collagen bundles were con-

Figure 6. Hair follicle connected with mature sebaceous gland (case 4). (hematoxylin and eosin, original magnification x 100) 579

International jnurnal of Dermatology Vol. 31, No. 8, August 1992

Table 1. The Clinical Characteristics of Previous Reported Cases and Our Cases Sex







4mm nodule



1cm tumor



3mm papule 1cm papule 20x15mm plaque 5mm papule 5mm papule 1cm plaque 7mm nodule

Flesh Erythema Slight Bluish Erythema Flesh Bluish erythema Flesh

(years) Reference 2



10 years

Reference 5



Since birth

Reference 3 Reference 6 Reference 4




40 18

Since birth 3 years 4 years

2.5cm below the Lt.preauricular area Rt. temple Lt. nasal bridge Lt.chin

4 43 37 19

6 months 2 years Since childhood Since birth

Rt. cheek Nasal tip Rt. nasolabial fold Lt. nostril

Case 1 Case 2 Case 3 Case 4



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Lever's textbook,^ the trichofolliculoma has a large cystic space lined by squamous epithelium and containing horny material, as well as fragments of birefringent hair shafts in the dermis, from which radiated many small, but usually fairly well-differentiated, secondary hair follicles. Pinkus and Mehregan' described hair nevus as the localized growth of unusually strong hairs and hair follicle nevus in the crowding of many tiny mature follicles. Pippione-' described pure hair follicle nevus as an extremely rare hamartoma that has peculiar features in the form of well-differentiated hair follicles, occasionally accompanied by sebaceous glands and pilar muscles, but without abnormalities of the acrotrichium. In Table 1 we characterized the clinical features of previously reported cases and our cases. The sex ratio was the same, and the age at onset ranged from birth to 41 years. We would not apply the term congenital hamartoma to hair follicle nevus. The site of predilection was the face in all reported cases, including ours. The skin lesions included papules, plaques, nodules, and tumors whose sizes were almost always within a diameter of 1 cm. The colors were flesh, erythematous.



Pruritus No

Pruritus No

Pruritus No

Figure 8. Smooth muscle bundle (case 4). (hematoxylin and eosin, original magnification x 400)

and bluish in order of frequency. Although most cases were symptomless, three cases including two of ours were pruritic, the color of the skin lesion was erythematous, and the histopathologic findings were dermal inflammatory cell infiltrations with epidermal changes such as acanthosis. These changes may have been due to external stimulation including itching. We observed the blood vessel dilation in three cases, smooth muscle in two cases, and striated muscle in one case. We found that the main components of hair follicle nevi were mature hair follicles and sebaceous glands, and the minor components were smooth muscle, striated muscle, which Kirihara et al.'' considered as ectopic hamartomatous proliferation, and dilated blood vessels.



Figure 7. Striated muscle bundles between hair follicles (case 4). (hematoxylin and eosin, original magnification x 400)



Pinkus H, Mehregan AH. Hair nevi and hair follicle tumors. In: Pinkus H, Mehregan AH, eds. A guide to dermatohistopathology. 3rd Ed. New York; AppletonCentury-Crofts 1981:423. Hyman AB, dayman SJ. Hair-follicle nevus. Arch Dermatol 1957; 93:678-684.

H.-iir Follicle Nevus Choi et Lil.

3. 4.

Pippione M, Aloi F, Depaoli MA. Hair-follicle nevus. Am J Dermatopathol 1984; 42:245-247. Kirihara Y, Suenaga Y, Take N. Hair follicle nevus

mal appendages. In: Lever WF, Schaumburg-Lever G, eds. Histopathology of the skin. 7th Ed. Philadelphia: JB Lippincott, 1990:580.

with hvperplasia of smooth and striated muscle, f DerI iTinrT ->/i ^n^ -7rvn

5. 6. 7.

„ o-

matol 1990; 30:696-700. Jo I, Hong NS, Seo EJ, Cho BK. A case ot hair follicle nevus. KorJ Dermatol 1983; 24:473-475. Kim DH, Chyung EJ, Park SY. A case of hair follicle nevus. KorJ Dermatol 1985; 26:711-713. Lever WE, Schaumburg-Lever G. Tumors of tbe epider-

I^TW t n- \ TT-T-II• r j Klignifln AM, Pmkus H. The bistogenesis ot nevoid tu-

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Gray HR, Helwig EB. Trichofoliiculoma. Arch Dermatol 1962; 98:619-625. 10. Headington JT. Tumors of tbe bair follicle. Am J Pathol 1976; 60:480-505.

IgE IgE is a 190,000 molecular weight antibody consisting of two light chains and two heavy chains, with a highly specialized Fc region that binds preferentially to mast cells, basophils, and certain lymphocytes. The Fc portion of the IgE molecule binds noncovalently to the receptor on the surface of mast cells, where it stays for days to weeks. Low-affinity macrophage IgE receptors are thought to take part in the destruction of parasites. The concentration of IgE in circulation is approximately 0.1 ^g/mL, the lowest of all antibodies. The small amount of circulating IgE is a reflection of its high affinity for receptors on mast cells and basophils and its low rate of synthesis. IgE in small amounts is normally produced after immunization and clears within 2 to 4 weeks. To stimulate the mast cell to secrete its mediator substances, two IgE molecules attached to the cell surface must be cross-linked. Only multivalent antigens can cross-link these antibodies. The resulting mediator release from mast cells causes an immediate hypersensitivity (type I) response. IgE levels in serum are increased with parasitic infection. IgE increases the number of eosinophils participating in killing parasites and also activates the eosinophils to be more efficient. IgE levels are also increased during bacterial infections, but investigators are uncertain about this role. In addition, increased IgE is associated with some cases of atopic dermatitis, incontinentia pigmenti, Wiskott-Aldrich syndrome, and the hyper-IgE syndrome, as well as some other disorders. Immediate hypersensitivity is an IgE-mediated, antigen-specific event. In this type of reaction, antigen is recognized by IgE molecules that have become attached to mast cells in the dermis. The mast cell has approximately 10''' receptors of IgE. When two molecules of IgE are cross-linked on a mast cell membrane, the contents of the mast cell granules are extruded and membrane changes are initiated. Granules contain several preformed mediators, including heparin, histamine, eosinophil chemotactic factor, neutrophil chemotactic factor, proteases, and glycosidases. Histamine acts as a vasodilator. It increases the permeability of vessels (by increasing spaces between endothelial cells), is chemotactic for eosinophils, and constricts smooth muscle. The interaction of IgE with antigen also causes changes within the cell membrane itself. Arachidonic acid (5-HETE) is oxidized by the cyclooxygenase system of the cell, producing several major mediators. One of these mediators is prostaglandin Di (PGDa), which acts as a vasodilator by contracting smooth muscle within the vessel wall. Prostaglandin D? is the predominant arachidonic metabolite made by mast cells. It has been shown to be a potent bronchial muscle constrictor and plays a part in anaphylaxis. LTC4, LTD4, and LTE4, formerly called SRS-A (slow-reacting substance of anaphylaxis), are also released. These agents comprise a family of leukotrienes that produce vasodilation and smooth muscle contraction, particularly in asthma. From Ray MC. Immunology overview. In: Ray MC, ed. Applied imtnunodermatology. New York: Igaku-Shoin, 1992:5. 581

Hair follicle nevus.

Four cases of hair follicle nevi are described. Hair follicle nevus is an extremely rare hamartoma occurring on the face, which has had no clear histo...
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