Acta Neurochir (Wien) (1991) 113:125-130 :Acta . . N urochlrurg ca 9 Springer-Verlag 199 t Printed in Austria Transtentorial Epidermoid Cysts P. Lunardi and P. Missori Department of Neurological Sciences, Neurosurgery, University of Rome "La Sapienza", Rome, Italy Summary Epidermoid cysts may occur simultaneously above and below the tentorium. Eleven patients with involvement of both infra- and supra-tentorial cisterns are presented. In two cases the epidermoid, located mainly in the cerebello-pontine angle, spread into the middle cranial fossa; in three the epidermoid extended from the parasellar cisterns to the posterior cranial fossa; in six patients the epidermoid, enlarging the tentorial notch, occupied extensively both cranial fos- sae. The surgical approach was influenced both by the experience of the surgeon and by the main extension of the epidermoid. Total removal was feasible in two patients only but only one of the eleven patients had a recurrence of the epidermoid. The long term results appear to be unrelated to the size of the epidermoid and to the choice of approach. Keywords: Ambient cistern; computed tomography; epidermoid cyst; magnetic resonance imaging; subarachnoid space; surgical ap- proach. Introduction Intracranial epidermoids are extra-axial subarach- noid lesions of dysembryogenetic origin with no ten- dency to infiltrate. Their slow growth and the soft con- sistency of cholesterin allow progressive adaptation to the neurovascular structures with preferential devel- opment along natural pathways, that is, the sub- arachnoidal cisterns of the skull base. The cisterns of the cerebello-pontine angle and the parasellar cisterns are the most common sites of development for an epi- dermoid 4, 14, 21, 23, 24, 43, 51-53, 61 Through the ambient cistern, the lesion can spread to the supra- or infra- tentorial space, thus assuming a transtentorial config- uration. These lesions are thus also known as hourglass epidermoid cysts 1,40. Thanks to computed tomography (CT) and magnetic resonance imaging (MRI), they are being diagnosed with increasing frequency, although not more than 50 cases have been reported to date. We report here the surgical outcome in 11 patients operated on for transtentorial epidermoids and discuss the problems involved. Material and Method Between 1966 and 1989 in the Section of Neurosurgery, De- partment of Neurological Sciences of La Sapienza University of Rome, 11 patients with an intracranial intradural epidermoid cyst developing above and below the tentorium were treated surgically, i.e. 19% (11/57) of the cases of intracranial intradural epidermoid so treated (Table 1). According to the symptoms at onset (cerebello-pontine angle syndrome or temporal lobe epilepsy) and mode of growth ef the lesion, the patients have been classified into three groups: a) infra- tentorial epidermoids with supratentoriaI extension; b) supratento- rial epidermoids with infratentorial extension; c) giant epidermoids with considerable extension both above and below the tentorium. The long term surgical results have been rated as follows: ex- cellent (independence with no deficits); good (independence with slight deficits); fair (dependence with slight deficits); poor (depend- ence with severe deficits). Table I. Location of 57 Intradural Epidermoid Cysts Supratentorial Suprasellar-chiasmatic Parasellar-Sylvian-Lateral ventricle Convexity Third ventricle Transtentorial Infratentorial Cerebello-pontine angle Fourth ventricle CerebelIar hemisphere Total 3 13 2 1 11 I8 7 2 57