We report a case of a cutaneous fistula in a child's toe, along with a review of the literature. The patient was a 5-year-old boy whose mother noticed a depressed region at the base of the right first toe when he was 2 years old. The depression persisted with time, so he was referred to our department. During the initial visit, a cutaneous fistula with a diameter of 1 mm and a depth of 2 mm was observed at the base of the toe. Surgical excision was performed, and histopathological findings demonstratd that the fistula wall consisted of multilayered squamous epithelium with a prominent stratum corneum. Postoperative follow-up showed no recurrence. Cutaneous fistulas can be categorized as congenital or acquired. Congenital ear fistulas are caused by a failure of fusion of the auricular tubercle or remnants of the first branchial cleft during the development of the ear. No congenital cutaneous fistulas have been identified arising solely in the limbs. With regard to acquired fistulas, pilonidal sinus has been reported, as have underlying infections and foreign bodies, but none of these were present in our patient. Pilonidal sinuses can form fistulas, cysts, or granulomas containing hair; they occur predominantly in the sacral region, but rarely in the interdigital area. Eight cases have been reported between the fingers, and three between the toes since 2000, mostly in patients working in hair-related occupations, such as barbers, hairdressers, dog trimmers, and sheep shearers. Hair and wool have been identified within the fistulas in the lesions of those working in these occupations. With interdigital sinuses, it is believed that hair clippings penetrate the skin, causing foreign body reactions that result in fistulas which then spread as the hair repeatedly penetrates the fistulas via abrasions of the surrounding skin. In our patient, neither the affected child nor his family had a history of hair exposure or pet ownership. However, considering the lack of previous reports of congenital cutaneous fistulas of the toes and the unlikelihood of a cutaneous fistula developing naturally in such an anatomical site, we thought the probability of an acquired interdigital pilonidal sinus was high. Cutaneous fistulas occurring in the toes are rarely reported in the literature, and reports of more cases will be necessary to elucidate the pathogenesis of this disease.

【背景】

【症例】患者は34歳男性．3週間前より仙骨部に膨隆・疼痛が出現したため近医を受診し，

症例は5か月女児．生後2か月時に左側腹部の有毛性瘻孔に気付かれた．生後3か月時より瘻孔部の発赤を認めて抗菌薬治療が行われたが改善せずに当院紹介となった．初診時，瘻孔の周囲に約1 cmの皮下膿瘍を認めた．超音波検査で瘻孔は左腎下極レベルに存在し，背側へ約15 mm向かい胸腰筋膜の手前で盲端となっていた．炎症の消退後に施行したMRIで，深さ約17 mmの瘻孔は皮下脂肪内で盲端となり脊椎管との交通は認めなかった．その後も局所感染を繰り返したため生後5か月時に摘出手術を行った．瘻孔は皮下脂肪内で盲端に終わり全摘出できた．病理所見では角化を伴う重層扁平上皮で覆われ毛包を伴っており，先天性皮膚洞と考えられた．一般的に先天性皮膚洞は頭部からの仙尾部の正中皮膚に開口する小さな管腔あるいは陥凹とされている．本例は開口部が側腹部で非正中部と非常にまれな部位であったが，発症年齢より先天性皮膚洞と考えられた．