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Neuroradiology Case of the Week

Case 129

Sudhir Kathuria, MD, Jeevak Almast, MD
and Per-Lennart Westesson, MD, PhD, DDS

Clinical Presentation: An 8-week-old female child with achondroplasia, presenting with episodes of apnea.

Radiological Findings: MRI scan demonstrates anterior-posterior (AP) compression of the cervicomedullary junction with deformation of the shape of upper cervical cord. This narrowing is most significant between the transverse ligament and the posterior foramen magnum. The posterior fossa is smaller, with short clivus, long infundibulum, and normal pituitary gland. CT scan shows thickening of the posterior rim of foramen magnum.

Discussion: The central neurologic manifestations of achondroplasia in infants are related to abnormalities at the cranial base and compression of the medulla and upper cervical spinal cord. Defective enchondral bone formation at the skull base leads to a short basicranium, small clivus, shallow posterior fossa and narrowing of the foramen magnum [1]. The foramen magnum may be further compromised by the anterior extension of a squama of occiput or by thickening of posterior rim of the foramen magnum. Compression of medulla oblongata impairs the respiratory control mechanisms, resulting in apnea or sudden death [2,3].
      Some patients have severe compression of the cervicomedullary junctions and show no signs or symptoms. MRI of craniocervical junction allows accurate diagnosis even in asymptomatic patients with severe compression before respiratory complications develop or sudden death occurs. Dorsal decompression of the craniovertebral junction can be performed safely and avoids serious complications associated with cervicomedullary compression. Therefore, MRI along with clinical evaluation is recommended in all infants with achondroplasia [2].

References:

1. Pauli RM, Horton VK, Glinski LP, Reiser CA. Prospective assessment of risks for cervicomedullary junction compression in infants with achondroplasia. Am J Hum Genet 1995; 56:732-744. [Medline]
2. Keiper GL Jr, Koch B, Crone KR. Achondroplasia and cervicomedullary compression: prospective evaluation and surgical treatment. Pediatric Neurosurg 1999; 31: 78-83. [Medline]
3. Hecht JT, Butler IJ. Neurological morbidity associated with achondroplasia. J Child Neurol 1990; 5:84-97. [Medline]