Superficial cortical landmarks for localization of the hippocampus: Application for temporal lobectomy and amygdalohippocampectomy

Abstract

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.

Figure 1

The relationship of right hippocampus and temporal horn to the superficial structures. © The Neurosurgical Atlas, by Aaron A. Cohen-Gadol, MD, MSc, used with permission

Figure 2

Left hemisphere with pins noting the anterior, middle, and posterior parts of the hippocampus

Figure 3

Right hemisphere with pins noting the anterior, middle, and posterior parts of the hippocampus

Figure 4

Axial section through the right temporal lobe for verification of outer cortical landmarks to internally positioned hippocampus

Figure 5

Left hemisphere with pins marking the head and tail of the hippocampus. Here, the head (anterior pin) is seen at the level of the inferior temporal sulcus and the tail (posterior pin) is seen at the level of the lower part of the middle temporal gyrus

Figure 6

Right hemisphere with pins marking the head and tail of the hippocampus. In this specimen, the head (anterior pin) of the hippocampus is deep to the inferior temporal sulcus. However, the tail (posterior pin) is located in the superior temporal sulcus

Figure 7

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