THE ACQUIRED CHIARI MALFORMATION AND SYRINGOMYELIA FOLLOWING SPINAL CSF DRAINAGE - A STUDY OF INCIDENCE AND MANAGEMENT

Firstly, 14 patients are described who developed either an acquired Ch iari malformation (ACM) alone (7 cases) or ACM and syringomyelia (7cas es) after lumbar subarachnoid space (SAS) shunting or in one case, epi dural anaesthesia with SAS penetration. Four groups are considered: 3 cases with craniofacial dysostosis and communicating hydrocephalus (CH ), 4 cases with CH alone, 3 cases with pseudotumour cerebri (PTC) and a miscellaneous group (4 cases). Initial treatment was varied: resitin g the shunt to ventricle or cisterna magna [6], adding an H-V valve [1 ], syrinx shunting [4] and posterior fossa decompression [3]. Further treatment was required in 6 cases. Secondly, incidence was examined in 87 patients with PTC initially treated either by lumbar SAS shunting [70] or cisterna magna shunting [17]. In the first sub-group, 11 cases (15.7 per cent) developed an ACM, 3 symptomatic (as above) and eight asymptomatic with 1 case also having syringomyelia whereas 1 case occu rred in the second group with a questionanably symptomatic ACM. While accurate for symptomatic lesions, these figures are tentative with res pect to asymptomatic lesions due to inadequate pre-treatment radiology and detailed MR follow-up. The main conclusions are, first, that the incidence of symptomatic ACM and/or syringomyelia is not high enough t o warrant abandoning SAS shunting; second that. asymptomatic lesions n eed not necessarily be treated and third, that when treatment is requi red, shunt resiting is the first choice.