๐ ็ธฝ็ฎ้ ๏ฝ ๐ ่ฑๆๅๆ๏ผๆฌ็ฏ๏ผ ๏ฝ ๐ ๅฎๆด็ฟป่ญฏ ๏ฝ โญ ็ฒพ่ฏ็ญ่จ
Proliferating epidermoid cyst
Proliferating epidermoid cyst
Clinical features Proliferating epidermoid cyst is rare and poorly documented, with the majority of cases, in fact, describing the pilar/trichilemmal variant.1,2 There are, however, very occasional reports of this entity, of which the comprehensive review from the Armed Forces Institute of Pathology is the most informative.3,4
The tumor shows a predilection for males (1.8:1) and, although a wide variety of sites may be affected, the majority appear to present on the pelvic area, scalp, and trunk in descending order of frequency.4 Most patients are middle aged or elderly (range 21โ88 years, mean 54 years). Occasional patients document the presence of a lesion for several decades,
1684 Cutaneous cysts
giving support to the concept that the resulting tumor has developed within a preexistent benign epidermoid cyst.4 In this series, proliferating epidermoid cyst was associated with a 20% recurrence rate but metastases were not encountered.4
Histologic features By definition, focal cyst wall lined by stratified squamous epithelium and showing a granular cell layer with epidermoid/infundibular keratinization must be evident. The proliferating component is variable and ranges from well-differentiated squamous epithelium with conspicuous squamous eddies reminiscent of inverted follicular keratosis through to multicystic, keratotic, and verrucous lesions.4 Rarely, frank invasive carcinoma is encountered.
A lesion displaying melanocytic and sebaceous differentiation has been described.10
Differential diagnosis Verrucous cyst differs from HPV-associated epidermoid cysts of the sole, which predominantly affect the Japanese and in which the morphology of the wall of the cyst is that of a typical epidermoid cyst.11,12