Case report: imaging findings in a "butterfly" vertebra.

A "butterfly" vertebra is a rare congenital anomaly, presenting as a sagittal cleft in the vertebral body. In the literature it has been described as an isolated finding, but it can also be associated with various syndromes, such as Alagille, Jarcho-Levin, Crouzon and Pfeiffer syndrome. We present a case of a 35-year old man with chronic low back pain. The diagnosis of a butterfly vertebra of S1 with disc space narrowing of L5-S1 was made. Usually the abnormality occurs at the thoracolumbar spine and we are not aware of a description of a sacral butterfly vertebra. Although a butterfly vertebra is usually asymptomatic, it could lead to discal herniation or chronic back pain due to alteration in spinal biomechanics.