Microanatomic and vascular aspects of the temporomesial region.

OBJECTIVE The aim of this work was to provide a detailed description of the arterial vascularization of the temporomesial region (TMR), correlated with the definitions of the macroscopic and cytoarchitectonic subdivisions of this area. METHODS Selective colored arterial injections were performed in 16 hemispheres to study their blood supply. Four hemispheres were used to illustrate the macroscopic aspect of the TMR and were then cut into thin sections and stained with Nissl's stain to study the cytoarchitectonic areas. RESULTS The surface of the TMR is subdivided into several areas: anteriorly, the lateral olfactory gyrus is covered by prepiriform cortex; dorsomedially, the semilunar gyrus and uncus hippocampi consist, respectively, of cortical amygdaloid nucleus and hippocampal cytoarchitectonic fields; and ventrolaterally, the anterior part of the parahippocampal gyrus is covered by periamygdaloid cortex, entorhinal, and transentorhinal areas and its posterior part is covered by Fields TH and TF per Von Economo and subicular complex. Six cortical arterial groups were defined: Group I, anterosuperior parahippocampal arteries (mean, 3.9 arteries) vascularize the ambiens, semilunar, and lateral olfactory gyri (origins: middle cerebral artery, anterior choroidal artery [AChA], posterior cerebral artery [PCA], and internal carotid artery); Group II, anteroinferior parahippocampal arteries (mean, 2.8 arteries) irrigate the anterior ventrolateral region of the parahippocampal gyrus (origins: middle cerebral artery, PCA, and AChA); Group III, medial uncal arteries (mean, 1.9 arteries) supply the medial part of uncus hippocampi (origins: AChA and PCA); Group IV, lateral uncal arteries (mean, 2.9 arteries) vascularize the lateral part of the uncus hippocampi (origins: AChA and PCA); Group V, several small posterior parahippocampal arteries irrigate Fields TF and TH per Von Economo (origins: PCA and AChA); and Group VI, posterior hippocampal arteries (mean, 3.2 arteries) irrigate the posterior part of hippocampal formation (origin: PCA). Many anastomoses are found among these arteries, particularly in the ventrolateral part of the TMR. Three groups of amygdaloid arteries were defined: Group I, the anterolateral group (mean, 5.7 arteries) (origin: middle cerebral artery); Group II, the medial group (mean, 6.4 arteries) (origins: AChA, internal carotid artery, and PCA); and Group III, the posterolateral group (mean, 5 arteries) (origins: AChA and internal carotid artery). CONCLUSION We hope that this work will be useful for any microneurosurgical procedures on the TMR. We have clarified the macroscopic and histological definitions of the cortical and nuclear areas of the TMR and the arterial groups closely related to them. The systematic analysis of the variability of the arterial vascularization of this area was our second goal; such a goal, however, requires more observations to be exhaustive. The numerous interterritorial anastomoses found inside the TMR imply that a selective presurgical injection of short-acting barbiturates to evaluate its functions (Wada test) may well result in its diffusion to other areas of the TMR.