Upper cervical myelopathy in achondroplasia.

Two achondroplastic infants had small foramina magna with lethal compression of the corresponding upper cervical spinal cords. The damage was histologically comparable to the hyperextension type of spinal cord injury. An anterior displacement of the foramen magnum was demonstrated in one of the two cases. The displacement is considered worthy of future verification as it may be an additional factor in susceptibility to hyperextension injury to the spinal cord. The second patient survived 6 months, demonstrating that not all upper cervical spinal cord injuries are immediately fatal. Patients who have sublethal lesions are potentially salvageable by surgery. It is also speculated that there might be more cases of nonlethal upper cervical spinal-cord damage in achondroplasia, especially in early infancy when infants are unable to hold their heads erect. The true incidence of slight upper cervical spinal cord damage is not known, although it is considered rare at present. As a result of the findings in these two cases, it is suggested that hyperextension of the head be avoided, when possible.