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CERVICAL CORD COMPRESSION IN ACHONDROPLASIA

Cervicomedullary cord compression due to an abnormally small foramen magnum (FM) has been thought to be rare in achondroplasia during childhood. Since autopsy-proven cases of cord compression have had apnea or other serious respiratory complications in the absence of specific neurologic signs, evaluation of patients with respiratory symptoms might reveal occult cord compression early in its course. With this in mind, we evaluated 10 children with achondroplasia (6 males, 4 females; ages 4 mos - 6yrs) for potential cervical cord compression; using CT, somatosensory evoked potentials (SEP) and brainstem auditory evoked responses (BAER). 2/10 patients were asymptomatic and 8/10 had respiratory problems. All 10 were hypotonic, but only 3 had focal neurologic findings. In 9/10, sagittal diameter of the FM was > 3 S.D. smaller than normal and an abnormal keyhole shape was seen. Moreover, in 4/10, sagittal CT reconstructions showed virtually no subarachnoid space posterior to the cord at the FM. The same 4/10 had prolonged latency on SEP; when contrasted with normal BAER in 10/10, this suggested cord dysfunction at the level of the FM. Metrizamide CT myelography confirmed and delineated the extent of cord compression in these 4. All 4 had respiratory abnormalities but only 2 had specific neurologic findings. This suggests that cervicomedullary cord compression may occur without neurologic findings and lead to respiratory problems in a significant number of achondroplastic children.