Acta Neurochir (Wien) (1994) 128:122-125 :Acta . . Nduro&lrurg ca 9 Springer-Verlag 1994 Printed in Austria Long-Term Evaluation of Asymptomatic Patients Operated on for Intracranial Epidermoid Cysts Comparison of the Diagostic Value of Magnetic Resonance Imaging and Computer-Assisted Cisternography for Detection of Cholesterin Fragments P. Lunardi,A. Fortuna, G. Cantore, and P. Missori Department of Neurological Sciences, Neurosurgery, University of Rome "La Sapienza", Italy Summary Magnetic resonance imaging (MRI) and/or computer-assisted cisternography (CAc) assessment of latent late recurrences in long- term asymptomatic patients surgically treated for intracranial epi- dermoid cyst is here presented. MRI was exclusively utilized in one patient; CAc was exclusively employed in three patients with metalic operative clips; both CAc and MRI were employed in another four patients. CAc appears to be more reliable than MRI in detecting cholesterin fragments in asymptomatic patients operated on for intracranial epidermoid cyst. Keywords." Cisternography; computerized assisted tomography; epidermoid cyst; magnetic resonance imaging; recurrence. Introduction It is well known that intracranial epidermoid cysts are benign lesions. Although their avascular and soft consistency generally allows an overall easy surgical removal, the ominous problem which fundamentally besets the surgeon is the detachment of the tumour's capsule, which frequently adheres to the perforating arteries, brain stem or floor of the fourth ventricle. To be sure, this proliferating neoplastic component must be completely removed in order to avoid recurrence 4' 10, 29, 31, 33, 37, 39, 40. If complete removal of the entire capsule and cholesterin cannot be accomplished, these patients are followed up for incipient symptoms or signs of recurrence 2' 6, lO, 14, 40. In this respect it has been pointed out that epidermoid cysts exhibit a linear growth rate, analogous to that of normal human skin, rather than exponential proliferation, proper to most tumours; thus a single measurement of the tumour size suffices for the calculation of the growth rate in any one particular case 3. Nevertheless, postoperative re- growth of epidermoid cyst is dependent on the amount of capsule left in situ, the degree of blood supply and surgical trauma incurred 22. Computerized neuroradiological imaging has been used to assess long-term postoperative evolution of the lesion 1,2, 33, 40. However, the residual space after tumour removal fills with cerebrospinal fluid. On computed tomography (CT) this is seen as a low density area resembling the original tumour, and may be, thus, con- fused with recurrence 31. In this case the intrathecal injection of a water-soluble contrast agent may differ- entiate cholesterin from cerebrospinal fluid. If pre-op- eratively MR! is regarded as a superior evaluating tool with respect to CT 21'26, this is not the case in a recurrent epidermoid cyst where the anatomical boundaries of the tumoural tissue are not well defined in a clear cut fashion. The low intensity on T 1-weighted images and high intensity on T 2-weighted images resembling cere- brospinal fluid around a mass, the irregular margins, the inhomogeneous appearance, the long sustained dis- placement of the brain, and the postoperative arach- noid adhesions may all veil the presence and/or true extension of the recurring epidermoid cyst. Twenty-three patients, from a group of sixty-four patients operated on for intracranial epidermoid cyst between 1952 and 1991 in our Department, had partial removal of the capsule. Out of this group, eight ran- domly selected asymptomatic patients underwent MRI and/or CAc to discover cholesterin in the subarachnoid spaces. One patient underwent only MRI, three only CAc, four both MRI and CAc.