Sacral agenesis with club shaped conus.

Dear Sir,

A 4-month-old boy presented with club feet and flattened buttock. The antenatal period was normal without a history of exposure to radiation, toxins, drugs or intrauterine infections or gestational diabetes. At birth parents noticed bilateral club feet with flattened buttocks. His motor, language and social development were normal. He had equinovarus deformity of left foot with reduced gluteal mass and abnormal skin folds over the buttocks [Figure 1a], without any evidence of spina bifida, dimple or dermal sinus or other bony deformity. His other systemic examination as well as 2D echo and ultrasound abdomen was normal. Radiograph pelvis showed total absence of sacral bones with iliac wings fused to lateral borders of lower most vertebras with normal transverse pelvic diameter. Magnetic resonance imaging of spine revealed sacral agenesis (SA) with abruptly ending club shaped conus at the level of T11 [Figure 1b–d].

Figure 1

(a) Clinical photograph showing flattened buttocks, shallow gluteal fold, (b) T2 weighted sagittal image of lumbosacral spine shows non tapering conus medullaris at upper border of D11 vertebral body (c) wedge shape of conus is due to dorsal half extending further than ventral half and is due to relative preservation of dorsal sacral roots and dorsal ganglia central T2 hyperintensity might be due to prominent terminal ventricle. Stretched out nerve roots are seen distally with narrow distal canal (d) radiograph pelvis anteroposterior view shows total absence of sacral bones with iliac wings fused to lateral borders of lower vertebra with normal transverse pelvic diameter

SA is a rare congenital disorder which involves absence of only coccyx to sacral, lumbar and even thoracic vertebrae with incidence of 0.01-0.05/1000 live births.[12] The exact etiology is not known but is reported in association with maternal diabetes, genetic factors and vascular hypoperfusion. Nearly 12-22% of SA cases are associated with maternal diabetes mellitus.[3] The clinical presentation varies from flattened buttocks with abnormal skin fold, shortening of the intergluteal cleft, small gluteal masses and club feet to severe form with genitourinary, respiratory and nervous system abnormalities. The position of conus defines two distinct groups in patients with SA. In group 1, conus terminate abruptly at T11 or T12 vertebral body level with club/wedge shape while in group 2 conus ends below L2 with tethered cord.[4] In our case, S1 vertebral body is absent suggesting high bony aplasia.