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Tailgut cysts are rare benign cystic lesions of the retrorectal space. The recommended treatment is complete resection because these cysts have occasionally shown malignant transformation. However, a high index of clinical suspicion is required to reach a diagnosis. We report a 68-year-old man complaining of a subcutaneous mass in his right buttock. Magnetic resonance imaging (MRI) showed a large cystic mass extending 25.7 cm from the pelvis to the buttock. Radiological features indicated a benign cystic tumor, but the level of serum carcinoembryonic antigen (CEA) (87.5 ng/mL) was increased. An incisional biopsy did not define the true histological nature of the lesion and was not useful for surgical planning. Although MRI could not detect malignant changes, the elevated serum CEA indicated malignant degeneration. The patient required a Miles operation for complete resection. Surgical pathology revealed focal areas of high-grade adenomatous and adenocarcinomatous changes in the cyst wall. After surgery, the serum CEA level decreased to below the normal range. The case presented here shows that early malignant degeneration of TGC is difficult to detect by MRI. Thus, a tailgut cyst should be completely removed, even if radiological examination cannot detect malignant features. Measurement of serum CEA may be helpful when the tumor expresses this antigen.

Common acquired skin diseases with a polygenic background, such as lichen planus, may show linear or segmental manifestations of underlying systemic skin disease. The linear arrangement in such cases is usually consistent with the lines of Blaschko. Happle summarized the various types of segmental arrangement of common polygenic diseases and proposed a novel designation of superimposed segmental dermatosis. Here, we report a unilateral linear dermatitis distributed along the lines of Blaschko on the leg, which was not self-healing and persisted for at least 6 years without complete remission, and was accompanied by preceding chronic prurigo on the extremities. Histological examination showed subacute spongiotic dermatitis and epidermal infiltration of CD4-positive cells. This case report presents a superimposed segmental dermatitis that arose based on systemic eczematous conditions, such as chronic prurigo.

Severe local skin reactions to subcutaneous injection of interferon beta-1b in multiple sclerosis are rare, and only 12 cases of severe skin reaction due to interferon beta-1b have been reported to date. We report two cases of severe skin reactions in multiple sclerosis patients following the injection of subcutaneous interferon beta-1b. In case 1, after five years of treatment, a painful indurated erythematous lesion appeared at the injection site on the left buttock. On histological analysis, the lesion showed septal and lobular panniculitis with lymphocytic infiltration. In case 2, cutaneous ulceration was surrounded by painful induration, which developed at the injection site on the right thigh after four years of treatment. The lesions resolved rapidly after discontinuation of interferon beta-1b treatment in both cases. Here, we review cases of similar lesions caused by interferon beta-1b reported in the literature, and discuss the characteristics, mechanism, treatment, and prevention of such lesions.