We report the case of a 16 year-old male with an asymptomatic alopecic plaque on the right parietal region of the scalp. A soft, domed, erythematous, and slightly alopecic nodule of 3cm in diameter surrounded by normal scalp was palpable on examination (Fig. 1). Biopsy showed an inflammatory lesion in the mid and deep dermis composed of granulation tissue, edema, reactive angioproliferation, and non-confluent granulomas, some with giant cells and others with central abscess formation (Fig. 2). Specific staining for microorganisms with Periodic acid Schiff (PAS), silver, Giemsa, and Ziehl-Neelsen was negative, as were mycological and bacteriological cultures. Treatment was initiated with doxycycline (100mg/d). Puncture of the lesion 2 weeks later revealed a yellowish orange material. After completing 2 months of treatment, the lesion resolved without scarring alopecia. No recurrence was observed after 5 months.

Figure 1.

A, Clinical appearance of alopecic nodule of the scalp. B, Drainage of yellowish material after puncture.

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Figure 2.

Histopathology: inflammatory lesion in the mid and deep dermis consisting of granulation tissue, edema, reactive angioproliferation, and mixed inflammatory infiltrate, with non-confluent granulomas, some with giant cells and others with central abscess formation (hematoxylin eosin, original magnification ×20).

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This condition most often affects young males and presents as alopecic, dome-shaped nodules surrounded by normal skin; it can be asymptomatic or cause occasional discomfort.2,4 Hair loss coincides with the formation of the nodules, which are located mainly at the vertex, but can occur in any area of the scalp. Usually 1 to 2 nodules develop as an isolated event, although some cases involve recurring nodules5; the nodules heal without causing scarring alopecia.

When material is obtained on puncturing the nodule, it can be serous, purulent, or yellowish, depending on the characteristics of the infiltrate and the type of vessel eroded by the infiltrate; yellow indicates erosion of a lymph vessel, as in the present case; pink indicates erosion of a blood vessel; and purulent material indicates the predominance of polymorphonuclear infiltrate.4 Cultures are negative in all cases.

Histologically these nodules exhibit mixed inflammatory infiltrates (lymphocytes, histiocytes, and giant cells) and in most cases granulomas in the deep dermis or pseudocyst-like architecture without a true wall. Histological differences are thought to be due to race-related differences in hair type or the comparison of superficial with nonsuperficial samples.4

These nodules respond well to treatment with doxycycline (100mg/d),4 intralesional corticosteroids,5 and aspiration or drainage of the nodule.2 Cases of spontaneous regression have been described,5 and in general surgical excision is not necessary.

While the etiology of AANS is unknown, it is considered to be a type of deep folliculitis secondary to follicular occlusion or a foreign body reaction. It is characterized by a granulomatous reaction with inflammatory infiltrate composed of lymphocytes, histiocytes, and giant cells. Subsequent central necrosis and erosion of blood and lymph vessels results in exudate production and pseudocyst formation. Some authors have suggested that AANS may lie within the spectrum of diseases associated with follicular occlusion, although immunological processes cannot be ruled out.3,6

Differential diagnosis with superinfected trichilemmal cyst, alopecia areata, bacterial and dermatophyte folliculitis, metastasis, and dissecting cellulitis should be established. Dissecting cellulitis, unlike AANS, presents clinically as multiple, painful, erythematous nodules, which form abscesses that fistulize and cause scarring alopecia.7

We agree with Abdennader and coworkers that alopecic and aseptic nodules of the scalp and pseudocyst of the scalp are the same entity, the former being a more appropriate name, as the nodules are always alopecic, the material obtained on puncturing the nodule is sterile, and histopathology does not always reveal pseudocysts.4 However, Sang Sing and coworkers6 argue that the 2 are distinct conditions, as biopsies reveal pseudocysts in the latter but not in the former.

In conclusion, AANS is an emerging entity in the literature, is relatively unknown, and thus is likely underdiagnosed. It is diagnosed by the presence of alopecic, aseptic nodules on the scalp and the absence of scarring alopecia. In general, it is easily managed and responds well to treatment. A better understanding of this condition is necessary for proper treatment and to avoid unnecessary interventions.