What causes butterfly vertebra in the spine on anteroposterior radiograph?
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Butterfly vertebra is a rare congenital vertebral anomaly characterized by a midline sagittal cleft in the vertebral body due to failure of fusion of the lateral halves during embryonic development, typically between the third and sixth weeks of gestation; it is usually asymptomatic but may be associated with spinal deformities such as congenital kyphosis, disc space narrowing, chronic back pain, or syndromic conditions including Alagille, Jarcho-Levin, Crouzon, and Pfeiffer syndromes, and most commonly affects the thoracic or lumbar spine, particularly T1.
Why is it called so?
The name derives from the characteristic butterfly-like configuration of the vertebral body on an anteroposterior radiograph, where the two symmetrical lateral halves resemble open butterfly wings separated by a central cleft.
Pathophysiology
The vertebral body forms from fusion of bilateral sclerotomes derived from somites; failure of midline fusion leaves a persistent sagittal cleft often filled with fibrous, cartilaginous, or notochordal tissue, leading to sclerotic lateral margins, widening of the affected vertebral body, concavities in adjacent endplates, and potential anterior wedge deformity resulting in kyphosis.
Alternative names: Sagittal cleft vertebra, anterior rachischisis
Other associated named signs: None
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