SURGICAL ANATOMY AND TECHNIQUES MICROSURGICAL APPROACHES TO THE MEDIAL TEMPORAL REGION:AN ANATOMICAL STUDY Alvaro Campero, M.D. OBJECTIVE: To describe the surgical anatomy of the anterior, middle, and posterior Department of Neurological Surgery, portions of the medial temporal region and to present an anatomic-based classification University of Florida, of the approaches to this area. Gainesville, Florida METHODS: Twenty formalin-fixed, adult cadaveric specimens were studied. Ten brains Gustavo Tro´ccoli, M.D. provided measurements to compare different surgical strategies. Approaches were demon- Department of Neurological Surgery, strated using 10 silicon-injected cadaveric heads. Surgical cases were used to illustrate the Hospital “Dr. J. Penna,” results by the different approaches. Transverse lines at the level of the inferior choroidal point Bahı´a Blanca, Argentina and quadrigeminal plate were used to divide the medial temporal region into anterior, middle, and posterior portions. Surgical approaches to the medial temporal region were classified into Carolina Martins, M.D. four groups: superior, lateral, basal, and medial, based on the surface of the lobe through which Department of Neurological Surgery, University of Florida, the approach was directed. The approaches through the medial group were subdivided further Gainesville, Florida into an anterior approach, the transsylvian transcisternal approach, and two posterior ap- proaches, the occipital interhemispheric and supracerebellar transtentorial approaches. Juan C. Fernandez-Miranda, M.D. RESULTS: The anterior portion of the medial temporal region can be reached through Department of Neurological Surgery, University of Florida, the superior, lateral, and basal surfaces of the lobe and the anterior variant of the Gainesville, Florida approach through the medial surface. The posterior group of approaches directed through the medial surface are useful for lesions located in the posterior portion. The Alexandre Yasuda, M.D., Ph.D. middle part of the medial temporal region is the most challenging area to expose, Department of Neurological Surgery, where the approach must be tailored according to the nature of the lesion and its University of Florida, extension to other medial temporal areas. Gainesville, Florida CONCLUSION: Each approach to medial temporal lesions has technical or functional Albert L. Rhoton, Jr., M.D. drawbacks that should be considered when selecting a surgical treatment for a given Department of Neurological Surgery, patient. Dividing the medial temporal region into smaller areas allows for a more University of Florida, precise analysis, not only of the expected anatomic relationships, but also of the Gainesville, Florida possible choices for the safe resection of the lesion. The systematization used here also Reprint requests: provides the basis for selection of a combination of approaches. Albert L. Rhoton, Jr., M.D., KEY WORDS: Medial temporal region, Microsurgical anatomy, Surgical approaches, Temporal lobe Department of Neurosurgery, University of Florida, Neurosurgery 59[ONS Suppl 4]:ONS-279–ONS-308, 2006 DOI: 10.1227/01.NEU.0000223509.21474.2E McKnight Brain Institute, P.O. Box 100265, Gainesville, FL 32610. Email: [email protected] he medial temporal region is the site of gion (1, 2, 4, 7–11, 13–28, 30, 33, 34, 36–38, the most complex cortical anatomy. It 40–42, 45–48, 52, 53). This study had three Received, January 13, 2006. is hidden deep within the remainder of goals: to examine the surgical approaches to Accepted, April 6, 2006. T the temporal lobe and ventricular system in the area, to divide the approaches into the margin of the basal cisterns and is sur- groups based on their anatomic characteris- rounded by vascular and neural elements tics, and to review the advantages and dis- that, unless required for treatment, must be advantages of the approaches in relation to preserved during surgery. Selecting and the part of the medial temporal region to be completing a surgical approach to the me- accessed. dial temporal region remains a challenge because of this anatomic complexity and MATERIALS AND METHODS deep location. There are many articles focus- ing on the anatomy, physiology, and surgi- Ten adult, formalin-fixed, cadaveric heads cal approaches to the medial temporal re- and 10 brains were studied. Coronal cuts, at NEUROSURGERY VOLUME 59 | OPERATIVE NEUROSURGERY 4 | OCTOBER 2006 | ONS-279 CAMPERO ET AL. the level of the apex of uncus and inferior choroidal point, were is directed, are divided into four groups: superior, lateral, performed in the 10 brains and distances between the temporal basal, and medial. The superior group includes only the lobe surface and temporal horn in each approach were mea- transsylvian-transinsular approach. The lateral group in- sured. Ten silicon-injected heads, dissected using the magnifica- cludes the approaches through the sulci and gyri on the tion of the surgical microscope (ϫ3–40; Carl Zeiss, Inc., Thorn- lateral surface of the temporal lobe and anterior temporal wood, NY), were used to demonstrate the surgical approaches. lobectomy with amygdalohippocampectomy. The basal Clinical examples of selected approaches are presented. group is comprised of the approach through the occipito- temporal, collateral, or rhinal sulci or through the fusiform RESULTS and parahippocampal gyri. The medial group is subdivided in an anterior variant, the transsylvian transcisternal ap- The surgical approaches to the medial temporal region, proach, and posterior variants, the occipito interhemi- based on the temporal surface, through which the approach spheric and supracerebellar transtentorial approaches. 3 FIGURE 1. Dissection photographs. A, the relationships of the tempo- preserved. The inferior choroidal point, the anterior end of the plexal ral lobe and horn, cranial sutures, and cortical surfaces of the right attachment in the temporal horn, is positioned behind the hippocampal side. The coronal, sagittal, squamosal, and lambdoid sutures and the head. The collateral eminence, located on the lateral side of the hip- superior temporal line have been preserved and the dura has been pocampus, overlies the deep end of the collateral sulcus. F, that the opened. The pterion is located at the lateral margin of the sphenoid choroid plexus has been removed in another specimen to expose the ridge near the junction of the coronal, squamosal, and frontosphenoid choroidal fissure located between the thalamus and fornix. The amyg- sutures and the lateral end of the greater sphenoid wing and stem of dala forms the anterior wall of the frontal horn. The uncal recess the sylvian fissure. The squamosal suture follows the anterior part of extends medially between the hippocampal head and the amygdala. The the posterior limb of the sylvian fissure before turning downward, at uncal recess is positioned lateral to the apex of the uncus. The upper the level of the postcentral and supramarginal gyri, to cross the junc- surface of the parahippocampal gyrus is exposed medial to the fimbria. tion of the middle and posterior third of the temporal lobe. The pole of G, the enlarged view of another specimen. The choroidal fissure the temporal pole fits into the cupped inner surface of the greater wing extends from the foramen of Monro to the inferior choroidal point of the sphenoid bone. Most of the lateral surface of the temporal lobe is located behind the head of the hippocampus. The choroid plexus, which positioned deep to the squamous part of the temporal bone; however, attaches along the choroidal fissure, has been removed. The lower edge the posterior part of the lateral surface extends beyond the posterior of the choroidal fissure in the temporal horn is formed by the fimbria limit of the squamous suture, deep to the parietal bone. The basal sur- of the fornix and the upper edge is formed by the thalamus. Opening face of the temporal lobe sits on the floor of the middle fossa and is the fissure between the lower surface of the thalamus and the fimbria positioned at the level of the upper edge of the zygomatic arch. B, the of the fornix exposes the ambient cistern. The lateral geniculate body anterior view of a coronal section, at the level of the sylvian fissure on is exposed at the lower margin of the thalamus in the upper wall of the right side and the sphenoid ridge in the left side. The pole of the the ambient cistern. The anterior wall of the temporal horn is formed temporal lobe extends forward under the sphenoid ridge and below the by the amygdala, which tilts backward above, but is separated from the sylvian fissure. The inferolateral edge of the temporal lobe is positioned hippocampal head by the temporal horn. The uncal recess extends at the lateral edge of the floor of the middle fossa at the level of the medially between the head of the hippocampus and amygdala. H, the zygomatic arch. C, the lateral view of the right temporal lobe. The superior view of a transverse section through the right temporal horn. temporal convexity is composed of the superior, middle, and inferior The hippocampus and collateral eminence form the floor of the tempo- temporal gyri, which are divided by the superior and inferior temporal ral horn. The amygdala occupies the anterior segment and the head of gyri. The inferior temporal gyrus folds around the lower margin of the hippocampus occupies the posterior segment of the uncus. The the hemisphere onto the lateral part of the basal hemispheric surface. apex of the uncus is directed medially at the level of the uncal recess. The supramarginal gyrus wraps around the upturned posterior end of The fimbria arises on the surface of the hippocampus. The upper sur- the sylvian fissure. D, that the frontal and parietal lobes, above the face of the parahippocampal gyrus is exposed medial to the fimbria. level of the sylvian fissure, have been removed. The upper lip of the The collateral eminence overlies the deep end of the collateral sulcus, calcarine sulcus, formed by the cuneus, has been removed to expose the which extends along the basal surface on the lateral side of the para- lingula that forms the lower bank of the calcarine sulcus.