The most appropriate surgical technique for posterior fossa
decompression in Chiari malformation (CM) remains a matter of debate. Intraoperative electrophysiological studies during posterior fossa
decompression of Type I CM (CM-I) aim to shed light on the entity's pathomechanism as well as on the ideal extent of
decompression. The existing reports on this issue state that significant improvement in conduction occurs after
craniotomy in all cases, but additional durotomy contributes a further improvement in only a minority of cases. This implies that
craniotomy alone might suffice for clinical improvement without the need of duraplasty or even subarachnoid manipulation at the level of the craniocervical junction. In contrast to published data, the authors describe the case of a 32-year-old woman who underwent surgery for CM associated with extensive cervicothoracic
syringomyelia and whose intraoperative somatosensory evoked potentials (SSEPs) did not notably improve after
craniotomy or following durotomy; rather, they only improved after opening of the fourth ventricle and restoration of CSF flow through the foramen of Magendie. Postoperatively, the patient recovered completely from her preoperative neurological deficits. To the authors' knowledge, this is the first report of significant SSEP recovery after opening the fourth ventricle in the
decompression of a CM-I. The electrophysiological and operative techniques are described in detail and the findings are discussed in the light of available literature. The authors conclude that there might be a subset of CM-I patients who require subarachnoid dissection at the level of the craniocervical junction to benefit clinically. Prospective studies with detailed electrophysiological analyses seem warranted to answer the question regarding the best surgical approach in CM-I
decompression.