The blue accessory digit.

At birth, an otherwise healthy term female infant was noted to have a 3 cm blue-coloured tense cyst-like lesion attached by a skin-coloured pedicle to the ulnar aspect of the right hand, adjacent to the fifth metacarpal–phalangeal joint (figure 1). Over the following 48 h, the cystic lesion involuted and appeared necrotic, but remained attached to the hand via a skin-coloured pedicle (figure 2). It eventually necrosed, shrinking in size and self-amputated on day 21. The infant was referred to a plastic surgeon for removal of the remaining pedicle. The differential diagnosis included an accessory digit or a fibrolipoma. The site and pedicle are typical of accessory digits, but the cystic nature and blue colour were unusual. A similar fibrolipoma lesion has been reported, but was located on the palmar surface. Histology of the lesion demonstrated necrotic, desiccated tissue composed of skin, connective tissue and a central area of partially ossified cartilage. The histology is consistent with a necrotic accessory digit. Simple fluid-filled cysts can appear blue due to the fluid within. We suggest that in this case, the blue cyst-like appearance is due to massive, localised tissue oedema caused by lymphatic obstruction. This is likely to have been either a developmental abnormality in the abnormal digit or torsion related. After birth, progressive necrosis would explain the alterations in appearance in the first few days.