Lipomatous Lumbar Mass with an Attached Digit and Associated Split Cord Malformation

BACKGROUND: A male infant was born with a digit attached to a skin-covered lumbar lipomatous mass and an underlying split cord malformation. METHODS: Surgical removal of the mass was performed at four months-of-age. By this time the digit had grown a nail and imaging and histology showed ongoing development of articulated phalanges. RESULTS: The lipomatous mass contained a long bone, a clavicle- and scapula-like structure and a variety of other mature germ layer derivatives. These features raised a number of diagnostic considerations, including: mature teratoma, hamartoma, rudimentary parasitic twin, lipomyelomeningocele and dorsal accessory limb. CONCLUSIONS: Based on review of the literature, the authors hypothesize that there is a pathogenetically related spectrum of skin-covered dorsal mass lesions, often associated with spinal dysraphism. These consist of a major lipomatous component and a variety of mature germ layer derivatives that can vary widely in their degree of anatomical organization from case to case.