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Case 90

Brainstem compression secondary to basilar impression.

A man with 5-6 month history of progressive dysphagia and suboccipital headache

Ozgur KILICKESMEZ, MD

This 52 year-old man presented with the symptoms of 5-6 month history of progressive slurred speech, dysphagia, neck pain spreading to the arms and suboccipital headache radiating to the skull vertex. The motor and sensory examination of the upper and lower extremities was unremarkable. There were no signs of hyperreflexia or myelopathy. An MRI study of the cranium was performed in three planes.

Findings

On the first image odontoid process seems to be displaced upon the Mc Gregor line nearly totally. The pathology may also be observed on the coronal T2 W image too. The pons is compressed and a secondary triventricular hydrocephalus had been developed.

Diagnosis

Brainstem compression secondary to basilar impression.

Discussion

Basilar invagination is the protrusion of odontoid process into the foramen magnum (McGregor's line is the line from posterior hard palate to base of occiput: if dens protrudes more than 4.5 mm then basilar invagination is diagnosed). The causes are condylus tertius, condylar hypoplasia, basiocciput hypoplasia and atlanto-occipital assimilation. The acquired form of basilar invagination is termed as basilar impression. The causes of the disease are Paget's disease, osteomalacia, rickets, fibrous dysplasia, hyperparathyroidism, Hurler syndrome, osteogenesis imperfecta and skull base infection. In basilar invagination symptoms become apparent when there is a great deal of flexion. It can present as posterior skull pain. A C2 sensory deficit should be looked for. Patients may also present with a "pseudo-ulnar hand", with tingling and numbness in the 4th and 5th digit and tingling and numbness in the medial forearm. Patients will go into a pool and notice that below the umbilicus the water is not as cold as it above (this suggests central cord disease). Lhermitte's sign (a tingling on neck movement, flexion in this case) can be demonstrated at any stage. Obstructive hydrocephalus or syringomyelia may also be seen because of direct mechanical blockage of normal CSF flow. A plain lateral x-ray with odontoid views, is a good place to start. Flexion exension MRI's have a higher yield. A plain CT scan can also document this, but MRI provides more information.

References

• Riew KD, Hilibrand AS, Palumbo MA, Sethi N, Bohlman HH. Diagnosing basilar invagination in the rheumatoid patient. The reliability of radiographic criteria. J Bone Joint Surg Am. 2001 Feb;83-A(2):194-200. PMID: 11216680
• Smoker WR. MR imaging of the craniovertebral junction. Magn Reson Imaging Clin N Am. 2000 Aug;8(3):635-50. Review.
• Naderi S, Pamir MN. Further cranial settling of the upper cervical spine following odontoidectomy. Report of two cases. J Neurosurg. 2001 Oct;95(2 Suppl):246-9. PMID: 11599846

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