The Diagnosis: Congenital Folliculosebaceous Cystic Hamartoma
Folliculosebaceous cystic hamartoma (FSCH) is a rare skin condition that is either congenital or acquired. It presents as a slow-growing and flesh-colored papulonodular lesion1 that mainly occurs on the head and neck. Involvement of the nipples, perineum, back, forearms, genital areas, and subcutaneous tissue also has been reported but usually indicates a larger lesion.1,2
Histologically, FSCH is considered a hamartoma composed of both ectodermal and mesodermal elements.1 Folliculosebaceous cystic hamartoma is a more complex lesion composed of infundibulocystic structures connected to maloriented folliculosebaceous units surrounded by whorls of highly vascularized fibrous stroma and adipocytes. Clefts between fibroepithelial units and surrounding stroma usually are present.1
Epithelial components contribute to the adnexal and folliculosebaceous cystic proliferations, and mesenchymal elements include vascular tissue, adipose tissue, and fibroblast-rich stroma.1,2 Acquired lesions arising in adults have been described,1-5 but the congenital presentation of FSCH in infancy is rare.
Histopathologically, some variations of FSCH are mainly composed of epithelial components while others are composed of nonepithelial components. Nonepithelial components include neural proliferation, muscle components, vascular proliferation, and mucin deposition.1-4 In some cases, FSCH may coexist with other diseases, such as nevus lipomatosus cutaneous superficialis and neurofibromatosis type I.4,5
In our case, histopathology showed several dermal infundibulocystic structures that were lined by stratified squamous epithelium and contained horny material (Figure 1). Numerous immature sebaceous lobules and rudimentary hair follicles emanated from some of the cyst walls. Mesenchymal changes around the fibroepithelial units included fibrillary bundles of collagen, clusters of adipocytes, and an increased number of small venules (Figure 2). In addition, the stroma adjacent to the malformed perifollicle contained some amount of mucin. Prominent clefts formed between fibroepithelial units and the surrounding altered stroma.
 Figure 1. Several dermal infundibulocystic structures were lined by stratified squamous epithelium and contained horny material (H&E, original magnification ×40) |  Figure 2. Ectopic focal adipocytes deposited in the dermis and among cystic structures. There were loose myxoid substance deposits prominently in perifollicle regions (H&E, original magnification ×200). | |
The differential diagnosis mainly includes sebaceous trichofolliculoma, molluscum contagiosum, dermoid cysts, pilomatrixoma, Spitz nevus, and nevus lipomatosus superficialis. The differential diagnosis between FSCH and sebaceous trichofolliculoma is challenging. Both lesions show an infundibular cyst and surrounding sebaceous nodules. According to Plewig,6 trichofolliculoma has a wide spectrum ranging from low to high differentiation represented by trichofolliculoma, sebaceous trichofolliculoma, and FSCH, respectively. It is not difficult to distinguish FSCH from other diseases according to its peculiar histopathologic features.
The clinicopathologic features of our case were similar to those of reported FSCH cases, except for the following unique characteristics: congenital lesion, lack of terminal hair, and no sebaceous material extrusion. These features of hair and sebaceous material may be correlated with the patient’s age and hormonal level.1 Androgen may play a key role in sebaceous gland development at puberty, which leads to sebaceous gland hyperplasia and hypertrophy. Therefore, slight pressure from the lesions can make ivory-white sebaceous material discharge. Hence, the dermatologist and pediatrician must be poised and sensitive while making an initial diagnosis of FSCH.