- Pediatric Neurosurgery, Children's Hospital of Alabama, Birmingham, Alabama, USA
- Department of Anatomic Sciences, St. George's University School of Medicine, St. George's, Grenada, UK
- Centre of Anatomy and Human Identification, University of Dundee, Scotland, UK
- Goodman Campbell Brain and Spine, Department of Neurological Surgery, Indiana University School of Medicine, Indianapolis, Indiana, USA
Aaron A. Cohen-Gadol
Goodman Campbell Brain and Spine, Department of Neurological Surgery, Indiana University School of Medicine, Indianapolis, Indiana, USA
DOI:10.4103/2152-7806.150663Copyright: © 2015 Tubbs RS. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
How to cite this article: Tubbs RS, Loukas M, Barbaro NM, Cohen-Gadol AA. Superficial cortical landmarks for localization of the hippocampus: Application for temporal lobectomy and amygdalohippocampectomy. Surg Neurol Int 03-Feb-2015;6:16
How to cite this URL: Tubbs RS, Loukas M, Barbaro NM, Cohen-Gadol AA. Superficial cortical landmarks for localization of the hippocampus: Application for temporal lobectomy and amygdalohippocampectomy. Surg Neurol Int 03-Feb-2015;6:16. Available from: http://sni.wpengine.com/surgicalint_articles/superficial-cortical-landmarks-for-localization-of-the-hippocampus-application-for-temporal-lobectomy-and-amygdalohippocampectomy/
Background:Accessing the hippocampus for amygdalohippocampectomy and procedures such as depth electrode placement requires accurate knowledge regarding the location of the hippocampus.
Methods:The authors removed 10 human cadaveric brains (20 sides) from their crania, noted relationships between the lateral temporal neocortex and underlying hippocampus, and measured the distance between the hippocampus and superficial landmarks.
Results:Mean distances were as follows: 3.8 cm from the tip of the temporal lobe to the head of the hippocampus; 6.5 cm from the tip of the temporal lobe to the junction of the fornix and hippocampus; and 3.5 cm between the tail and head of the hippocampus. The head of the hippocampus ranged from 0 to 5 mm inferior to the inferior temporal sulcus. The tail of the hippocampus ranged from 2.2 to 7 mm superior to the inferior temporal sulcus. In two specimens, the tail was deep to the superior temporal sulcus. Generally the length of the hippocampus was along the inferior temporal sulcus and inferior aspect of the middle temporal gyrus. The hippocampus tended to be more superiorly located and shorter in females and left sides, but this was not statistically significant.
Conclusions:Additional landmarks for localizing the underlying hippocampus may be helpful in temporal lobe surgery. Our study showed relatively constant anatomic landmarks between the hippocampus and overlying temporal cortex that may help localize the hippocampus during amygdalohippocampectomy and depth electrode implantation, verify the accuracy of image-guided methods, and used as adjuvant methodologies when these latter technologies are unavailable.
Keywords: Anatomy, epilepsy surgery, hippocampectomy, landmarks, neurosurgery, temporal lobe
Even with advancements in pharmacologic treatment of epilepsy, there is still a group of patients whose seizures have a higher tendency to be refractory to medical therapy. Medial temporal lobe epilepsy often is caused by medial temporal lobe sclerosis or lesional epileptogenic foci within the amygdala and hippocampal formation. The hippocampus and surrounding formation are made up of the cornu ammonis (hippocampus proper), subiculum, dentate gyrus, supracallosal gyrus, alveus, fimbria, and fornix.[
Anterior temporal lobectomy with amygdalohippocamectomy has proven efficacious for cessation of intractable seizures of medial temporal lobe origin. Aggressive resection of these medial temporal lobe structures has been associated with improved surgical outcomes.[
Ten formalin-fixed cadaveric brains (20 sides) were removed from the crania. The specimens were derived from six male and four female cadavers, aged 35–75 years (mean 65 years) at death. Brains were next hemisected in the midline and the fornix identified and followed toward the left and right hippocampus. Once the hippocampus was isolated from a mesial approach, 6-cm long straight needles were placed into its head, tail, and the midpoint between these structures, and passed laterally perpendicular to the cortical surface and until they reached the cortical surface. The specimens were turned over and the pin exit sites marked externally with smaller pins [Figures
We did not note any gross intracranial pathology or evidence of previous surgery in any specimen. The distance from the tip of the temporal lobe to the “head” of the hippocampus ranged from 3.5 to 4.3 cm (mean 3.8 cm) [Figures
In two right-sided specimens, the tail was deep to the superior temporal sulcus [
Localization of the hippocampus in relation to superficial structures is important for exposure of the hippocampus during anteromedial temporal lobectomy and amygdalohippocampectomy procedures while minimizing the extent of neocortical resection, especially on the dominant hemisphere. Furthermore, intraoperative depth electrodes placed within the hippocampus can provide useful information regarding the relative epileptogenecity of this medial structure versus the temporal neocortex. Therefore, it is important to localize the hippocampus as accurately as possible using all the available data, including image guidance and surface landmarks. In our study, we found that the inferior temporal sulcus and middle temporal gyrus were relatively constant landmarks to the underlying hippocampus. Additionally, and within a centimeter more or less, the length of the hippocampus was similar in length between sides and genders.
The hippocampus sits in the medial part of the temporal lobe and on the floor of the temporal horn of the lateral ventricle. The amygdala is situated anterior and superior to the head of hippocampus. The uncus, which is part of the entorhinal cortex, wraps around the inferior border of the hippocampus and appears as a continuous homogeneous ovoid mass with the amygdala on magnetic resonance imaging (MRI).[
Applications for selective amygdalohippocampectomy and depth electrode placement
The data presented about the localization of the “head” of the hippocampus 3–4 cm from the anterior temporal tip may have important implications regarding the extent of temporal neocortical resection necessary to perform an amygdalohippocampectomy. If a localized lesion is present along this anterior region, further neocortical resection will not be necessary. However, if an extensive hippocampectomy for medial temporal lobe sclerosis is contemplated, disconnection of the occipitotemporal fasciculus along the lateral aspect of the hippocampus will allow lateral mobilization the temporal cortex (instead of its resection), to provide enough exposure to allow for a posterior hippocampectomy [
Disconnection of the occipitotemporal fasciculus along the lateral aspect of the hippocampus will allow lateral mobilization the temporal cortex (instead of its resection), to provide enough exposure to allow for a posterior hippocampectomy. A corticotomy within the middle temporal gyrus, along the mid portion of the temporal lobe, will expose the ventricle. © The Neurosurgical Atlas, by Aaron A. Cohen-Gadol, MD, MSc, used with permission
In a study by Davies et al.,[
We performed the above cadaveric study to better identify the relationships between the outer temporal cortex and the deeper lying hippocampus. Such landmarks may be useful to neurosurgeons in localizing the hippocampus in conjunction with or to verify imaged-guided technologies or when these devices are not used or are unavailable.
The authors received no funding for this study and have no conflicts of interest in regard to this study and manuscript.
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