A rare incidental finding of an isolated S1 butterfly vertebra: A case report.

Butterfly vertebra is an uncommon type of vertebral anomaly (sometimes referred to as a sagittal cleft vertebra or an anterior rachischisis) caused by persistent notochordal tissue. Butterfly vertebrae of S1, which is rarer anomaly compared to thoraco-lumbar region, may be associated with syndromic causes and usually asymptomatic with a funnel shaped defect seen in imaging which can later give rise to disk problems, facet joint degeneration and chronic low back pain. We here share a case of 35-year female presented with intermittent low back pain diagnosed with S1 butterfly vertebrae as an incidental finding in radiograph and magnetic resonance imaging. Radiologist and orthopedicians should be vigilant about this rare entity as a differential of low back pain and its association with other syndromes.