Cervical high-intensity intramedullary lesions in achondroplasia: aetiology, prevalence and clinical relevance.

OBJECTIVES: In achondroplastic patients with slight complaints of medullary compression the cervical spinal cord regularly exhibits an intramedullary (CHII) lesion just below the craniocervical junction with no signs of focal compression on the cord. Currently, the prevalence of the lesion in the general achondroplastic population is studied and its origin is explored.

METHODS: Eighteen achondroplastic volunteers with merely no clinical signs of medullary compression were subjected to dynamic magnetic resonance imaging (MRI). The presence of a CHII lesion and craniocervical medullary compression in flexed and retroflexed craniocervical positions was explored. Several morphological characteristics of the craniocervical junction, possibly related to compression on the cord, were assessed.

RESULTS: A CHII lesion was observed in 39% of the subjects and in only one of these was compression at the craniocervical junction present. Consequently, no correlation between the CHII lesion and compression could be established. None of the morphological characteristics demonstrated a correlation with the CHII lesion, except thinning of the cord at the site of the CHII lesion.

CONCLUSIONS: CHII lesions are a frequent finding in achondroplasia, and are generally unaccompanied by clinical symptoms or compression on the cord. Further research focusing on the origin of CHII lesions and their clinical implications is warranted.

KEY POINTS: • MRI now reveals exquisite detail of the cervical spinal cord. • Cervical cord lesions are observed in one third of the achondroplastic population. • These lesions yield high signal intensity on T2 weighted MRI. • They are generally unaccompanied by clinical symptoms or cord compression. • Their aetiology is unclear and seems to be unrelated to mechanical causes.