Medial Temporal Lobe Tumors: Surgical Anatomy and Technique PDF

Medial Temporal Lobe Tumors: Surgical Anatomy and Technique Yuanzhi Xu, Maximiliano Alberto Nunez, Vera Vigo, and Juan C. Fernandez-Miranda Abbreviations PLHV po...

Medial Temporal Lobe Tumors: Surgical Anatomy and Technique Yuanzhi Xu, Maximiliano Alberto Nunez, Vera Vigo, and Juan C. Fernandez-Miranda Abbreviations PLHV posterior longitudinal hippocampal vein AChA anterior choroidal artery PLU posterior limit of the uncus AHA anterior hippocampal artery SA splenial artery AHPA anterior hippocampal- SAH selective amygdalohippocampectomy parahippocampal artery UHA uncohippocampal artery AHV anterior hippocampal vein AITA anterior-inferior temporal artery ALHV anterior longitudinal hippocampal vein 1 Introduction ITA inferior temporal artery LPChA lateral posterior choroidal artery The medial temporal lobe (MTL), also termed as MHA middle hippocampal artery the temporomesial or mediobasal temporal region MITA middle inferior temporal artery has the most intricate cortical anatomy. The MTL MTLE mesial temporal lobe epilepsy has a unique histological architecture with differ- MTR medial temporal region ent layers of mesocortex and isocortex (Fig. 1a). PCA posterior cerebral artery Thus, the MTL is highly related to the pathogen- PHA posterior hippocampal artery esis of epilepsy and tumors. The MTL is located PHPA posterior hippocampal- in the medial and inferior surface of the temporal parahippocampal artery lobe, and is separated from the thalamus by the PITA posterior-inferior temporal artery choroidal fissure. Since the MTL is located deep in the brain and is near vital neural and vascular elements, surgical removal carries considerable risk. It must be preserved during surgery unless it Y. Xu Department of Neurosurgery, Huashan Hospital, is necessary for treatment. Nevertheless, safe Shanghai Medical College, Fudan University, resection can be achieved with high knowledge Shanghai, China of the microsurgical anatomy of this region and Department of Neurosurgery, Stanford Hospital, choosing the right surgical approach to avoid Stanford, California, USA postoperative complications. M. A. Nunez · V. Vigo · J. C. Fernandez-Miranda (*) Here we give a comprehensive review on the Department of Neurosurgery, Stanford Hospital, cortical and subcortical features, arterial distribu- Stanford, California, USA tion, and venous drainage of MTL based on our e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 299 A. Shah et al. (eds.), Functional Anatomy of the Brain: A View from the Surgeon’s Eye, https://doi.org/10.1007/978-981-99-3412-6_14 300 Y. Xu et al. a b Fig. 1 Artistic illustration of MTL vascular pattern. (a) A., anterior hippocampal-parahippocampal artery; Ant. Medial view of anterior segment of MTL. The AChA Hippo. V., anterior hippocampal vein; Ant. Inf. Temp. A., gives off an anterior uncal artery that irrigates the semilu- anterior-inferior temporal artery; Ant. Long. Hippo. V., nar gyrus and an unco-hippocampal artery that irrigates anterior longitudinal hippocampal vein; Ant. Parahippo. the uncinate gyrus and band of Giacomini and penetrates A., anterior parahippocampal artery; AHA, anterior hip- the uncal sulcus to vascularize the extra-ventricular hip- pocampal artery; Calc. A., calcarine artery; Calc. Sulc., pocampal head. The ICA gives off an anterior uncal artery calcarine sulcus; Calc. V., calcarine vein; CN, cranial that supplies the semilunar gyrus. This branch usually is nerve; Coll. Sulc., collateral sulcus; Hippo. Head, hippo- present when the anterior uncal artery of the AChA is campal head; ICA, internal cerebral artery; Int.Cer.V., absent. An anterior uncal artery also arises from the M1 internal cerebral vein; L.P.Ch.A, lateral posterior choroi- segment of the MCA and supplies the ambient gyrus. An dal artery; MHA, middle hippocampal artery; Mid. Inf. unco-parahippocampal artery arises from the temporo- Temp. A., middle-inferior temporal artery; M.P.Ch.A, polar artery and irrigates both the ambient gyrus and the medial posterior choroidal artery; P.Comm.A., posterior anterior parahippocampal area. Branches from the P2a communicating artery; PHA, posterior hippocampal segment of the PCA irrigate the anterior parahippocampal artery; Post. Comm., posterior communicating; Post. region (anterior parahippocampal artery) or both the ante- Hippo. Parahippo. A., posterior hippocampal- rior para-hippocampal gyrus and hippocampal head (ante- parahippocampal artery; Post. Hippo. V., posterior hippo- rior hippocampal-parahippocampal artery). (b) Superior campal vein; Post. Inf. Temp. A., posterior-inferior view of ventricular vascular pattern of MTL, which com- temporal artery; Post. Long. Hippo. V., posterior longitu- posed of one uncohippocampal artery and one anterior dinal hippocampal vein; Pt., pituitary; Rec. A., recurrent hippocampal-parahippocampal artery in anterior segment artery; Splen. A., splenial artery; Sup. Coll., superior col- of MTL; two posterior hippocampal parahippocampal liculus; Sup. Temp., superior temporal; Unc. Hippo. A., arteries in the middle segment of MTL; and one posterior uncal hippocampal artery; V., vein. (With permission from hippocampal artery in the posterior segment of MTL. A. Juan Carlos Fernandez-Miranda, MD) Ch.A, anterior choroidal artery; Ant. Hippo. Parahippo. previous sequel publication [1, 2] (Fig. 1b), as ment starts from the posterior margin of the well as surgical implications when approaching uncus and terminates at approximate level of the the MTL via different approaches. quadrigeminal plate. The posterior segment begins at the quadrigeminal plate and terminates at the calcarine point, which is the intersection of 2 Neural Features of the MTL the calcarine sulcus and parieto-occipital sulcus (Fig. 2a). The MTL can be classified into three segments: anterior, middle, and posterior. There are cis- ternal and ventricular components in each 2.1 Anterior Segment segment. The anterior segment starts from the superior end of the rhinal sulcus and terminates at Uncus and entorhinal areas form the cisternal the posterior end of the uncus. The middle seg- elements of the anterior segment of the MTL. The Medial Temporal Lobe Tumors: Surgical Anatomy and Technique 301 a b c d Fig. 2 Neural features and subdivision of MTL. (a) campal head and body. The uncal sulcus, uncinate gyrus, Mediobasal view of the left cerebral hemisphere. The band of Giacomini, and intralimbic gyrus was involved MTR can be divided into 3 segments: anterior, middle, in extraventricular hippocampal head. (c) Enlarged view and posterior. The anterior segment extends posteriorly of middle segment of MTL. The extraventricular hippo- from where the rhinal sulcus turns upward at the posterior campal body is made of several structures, namely from edge of the temporal pole to a vertical line crossing the superior to inferior: the fimbria; the fibrio-dentate sulcus; posterior edge of the uncus. The middle segment extends the margo denticulatus, subiculum of parahippocampus posteriorly from the posterior edge of the uncus to a verti- and subsplenial gyrus. (d) Enlarged view of posterior seg- cal line at the level of the quadrigeminal plate. The pos- ment of MTL. Hippocampus tail is running caudo-medi- terior segment extends from the quadrigeminal plate to a ally in coronal, from the end of body to the terminal of vertical line passing through the calcarine point located at subsplenial gyrus. The extraventricular hippocampal tail the junction of the parieto-occipital and calcarine sulci. (b) consists of fasciola cinereal (FC) which is the smooth cau- Enlarged view of anterior segment of MTL. Hippocampus dal extension of the margo denticulatus; gyrus fasciolaris head is running rostro-medially from the uncal recess to (GF), the enlargement of fibrio-dentate sulcus posteriorly posterior limit of uncus (PLU) according its contour of extended; and the subsplenial gyrus, a prolongation of the digitations in the floor of temporal horn. Posterior limit gyrus fasciolaris, forms the end of the hippocampal tail, of uncus is the posterior end of uncus which located at the underneath the splenium, and continually extend with the site of anterior attachment end of the fimbria and posterior indusium griseum above the splenium. (With permission to intralimbic gyrus), served as a landmark to divid hippo- from Juan Carlos Fernandez-Miranda, MD) uncus is separated into anterior and posterior extra-ventricular elements of the hippocampal parts, which meet at uncal apex. Two minor gyri: head. The superior surface is bounded by the pos- the ambient and semilunar gyrus, demarcated by terior continuation of the entorhinal sulcus supe- the semiannular or amygdaloid sulcus, make up riorly semiannular sulcus anteriorly, the the anterior part of the uncus. The posterior part anterior-most part of the fimbria posteriorly, and of uncus is separated into upper and lower por- the uncal sulcus inferiorly. Three small gyri, from tions according to the uncal sulcus. There are two ventral to dorsal, uncinate gyrus, band of surfaces at the upper part: one superior and one Giacomini (terminal segment), and intralimbic inferior, which is composed by the gyrus are identified on upper part of posterior 302 Y. Xu et al. uncus [3, 4]. The parahippocampal gyrus Entorhinal Area constitutes the area below the uncal sulcus. The The entorhinal area, also known as Brodmann’s entorhinal area occupies the anterior parahippo- area 28, is a region of the allocortex found in the campal gyrus, lying medially to the rhinal sulcus anterior parahippocampal gyrus. It is located (Fig. 2b). inferiorly to the uncal apex and ambient gyrus, medially to the rhinal sulcus and anteriorly to the Semilunar Gyrus level of the posterior end of the uncus (as the pos- The semilunar gyrus, which appeared as a spheri- terior demarcation), which is considered corre- cal bulge on the upper aspect of the anterior spondently to the extra-ventricular bottom of uncus, covers the cortical amygdaloid nucleus. It hippocampal head. is separated by entorhinal sulcus from the ante- The ventricular elements of anterior segment rior perforated substance medially (Fig. 2b). of the MTL is formed predominantly by amyg- dala and hippocampus head. The hippocampus Ambient Gyrus head running rostro-medially from the uncal The ambient gyrus, composed mostly of entorhi- recess to posterior limit of uncus (PLU) according nal cortex, occupies the anterior, medial and infe- to its contour of digitations in the floor of tempo- rior portions of the anterior uncus. It is confined ral horn. Posterior limit of uncus is the posterior by the semilunar gyrus superiorly, the anterior end of uncus which is located at the site of ante- end of the uncal sulcus posteriorly and the tento- rior attachment end of the fimbria and posterior to rial edge inferiorly. The ambient gyrus joins the intralimbic gyrus, served as a landmark to divide entorhinal area of the parahippocampal gyrus hippocampal head and body. The character of anteroinferiorly and the limen insula and lateral intraventricular surface included hippocampal olfactory gyrus anterolaterally (Fig. 2b). digitations (also known as pes hippocampus) with the shallow longitudinal sulci which forms 2 or 3 Uncinate Gyrus small lobules on hippocampus head. The uncinate gyrus, considered as the anterior- most part of posterior uncus, is a protrusion situ- ated superiorly to anterior end of the uncal sulcus, 2.2 Middle Segment anteriorly to the band of Giacomini, and posteri- orly to the ambient gyrus (Fig. 2b). The middle segment of MTL is composed of cis- ternal and ventricular elements, and the former is Band of Giacomini built by posterior parahippocampal gyrus, which The band of Giacomini is the second prominence has 3 surfaces: superior, medial, and inferior. of posterior uncus above the uncal sulcus, which The fimbria of the fornix, the dentate gyrus and located between the uncinate gyrus and intralim- the subiculum, running from medial to lateral, bic gyrus. It is regarded as the extension of den- constitute the superior surface of middle seg- tate gyrus that travels vertically at the surface of ment. The fimbriodentate sulcus separates the the posterior uncus. fimbria from the dentate gyrus, whereas the hip- pocampal sulcus separates the dentate gyrus from Intralimbic Gyrus the subiculum. The superior and medial (consti- The intralimbic gyrus comprises the posterior- tuted mainly by the presubiculum) surface occu- most part of the posterior uncus, which func- pies the upper and lower part of ambient cistern, tioned as the anchor of anterior fimbria. The CA3 respectively. The inferior surface of middle seg- and CA4 sectors of hippocampus are located in ment, limited by the collateral sulcus laterally, intralimbic gyrus. faces the cerebellar tentorium, where the trajec- Medial Temporal Lobe Tumors: Surgical Anatomy and Technique 303 tory of superior petrosal sinus serves as a demar- dally. The calcar avis, posteriorly to collateral cation line for anterior and middle segments of trigone and inferiorly to the bulb of the corpus MTL (Fig. 2c). callosum, is the corresponding ventricle promi- The ventricular elements of middle segment nent structure of the ending calcarine sulcus, tra- of the MTL is built by choroidal fissure, hippo- ditionally known as the hippocampus minor. campus body and collateral eminence, from medial to lateral. The hippocampus body is a swiss roll appearance with two interlocking 3 Arterial Distribution U-shaped structures (dentate gyrus and cornu of the MTL ammonis), running sagittally from the PLU to the point the hippocampus turns caudo-medially in The AChA, ICA, MCA, and PCA were the arteries coronal. The intraventricular surface is the poste- most significantly implicated in the supply of the rior continuation of hippocampal digitations with MTL. Rich anastomoses among branches of the choroidal plexus above. main supplying arteries of the MTL were noted. Significantly, anastomoses form a complete arcade at hippocampal sulcus, and with the perfo- 2.3 Posterior Segment rated branch into hippocampus proper it forms a rake-like appearance (Figs. 1, 3, and 4). There are three cisternal surfaces in the posterior segment: medial, inferior and anterior. The calca- rine sulcus, the most important landmark on the 3.1 Anterior Choroidal Artery cisternal element splits the medial surface into a (AChA) superior portion, which is formed by parasplenial region including isthmus of the cingulate gyrus The anterior choroidal artery (AChA) origi- anteriorly and the inferior pole of the precuneus nates from the posterior wall of the ICA as a gyrus posteriorly, and an inferior portion, which single trunk (77%) in most cases. Two types of is composed by the anterior part of the lingual pseudoduplicated AChA are presented: one, gyrus. The anterior surface is hidden in the cleft consisting of 2 separate arteries arising from between splenium of the corpus callosum and the the ICA, and the other, consisting of a single isthmus of the cingulate gyrus, which is com- artery that immediately divides into 2 trunks. posed of the fornix crus and extraventricular por- Two segments comprise the course of AChA: tion of the hippocampal tail. Three anatomic the cisternal and plexal segment. The cisternal structures including fasciola cinereal (prolonga- segment of AChA, which starts from its ICA tion of dentate gyrus), fasciolaris gyrus (prolon- origin and ends at the inferior choroidal point, gation of fibrio-dentate sulcus) and subsplenial runs in the carotid cistern firstly then reaches gyrus (prolongation of fasciolaris gyrus), located the crural cistern between crus cerebri and from rostral to caudal, made up the extraventricu- uncus. The average length of cisternal segment lar portion of hippocampal tail. The crus of the is 23 mm (16–30 mm), and it gives an average fornix curves superomedially toward the inner of 9.5 branches (5–15 branches), which are surface of the splenium, wrapping around the divided into three groups depending on their posterior surface of the pulvinar to form choroi- distribution: (1) medial temporal group; (2) dal fissure (Fig. 2d). perforating group; and (3) choroidal branches The ventricular elements of posterior segment group. The medial temporal group can be of the MTL is composed by hippocampal tail, the subdivided into 3 subgroups according to the collateral trigone and calcar avis, rostrally to cau- destination: (1) anterosuperior subgroup to 304 Y. Xu et al. a b c d Fig. 3 Arterial Supply of anterior segment of MTL. (a) artery; Ant. Long. Hippo. V., anterior longitudinal hippo- Medioinferior view of the uncal sulcus shows 1 anterior campal vein; Ant. Parahippo. A., anterior parahippocam- hippocampal-parahippocampal artery (AHPA), originat- pal artery; AHA, anterior hippocampal artery; Basal V., ing from the AITA, penetrating the uncal sulcus to irrigate basal vein; Chor. Plex., choroid plexus; Coll. Sulc., col- the extraventricular part of the hippocampal head. (b) lateral sulcus; Entorhin. Area, entorhinal area; Mam. Inferiorly retraction of PCA showing the entry point of the Body, mamillary body; MHA, middle hippocampal AChA in the choroidal fissure at the inferior choroidal artery; Mid. Inf. Temp. A., middle-inferior temporal point. (c) Inferior view of anther specimen shows 1 AHPA artery; Parahippo. Gyrus, parahippocampal gyrus; PCA, and 1 UHA, entering the uncal sulcus. (d) Superior view posterior cerebral artery; P. Co. A., posterior communicat- of another dissected temporal lobe showing the ventricu- ing artery; PHA, posterior hippocampal artery; Post. lar features of MTL. The AChA and LPChA enter the lat- Hippo. Parahippo. A., posterior hippocampal- eral ventricle in the posterior limit of the uncus, supply the parahippocampal artery; Post. Inf. Temp. A., posterior- choroidal plexus. A.Ch.A, anterior choroidal artery; Ant. inferior temporal artery; Splen. A., splenial artery; Tent. Hippo. Parahippo. A., anterior hippocampal- Notch, tentorial notch; Uncal Sulc., uncal sulcus; Unc. parahippocampal artery; Ant. Hippo. V., anterior hippo- Hippo. A., uncal hippocampal artery. (With permission campal vein; Ant. Inf. Temp. A., anterior-inferior temporal from Juan Carlos Fernandez-Miranda, MD) anterior uncus, (2) medial subgroup to posterior arriving in foramen of Monro. According to our uncus, and (3) inferior subgroup to the entorhi- previous research, 38% AChA sent out perfo- nal area of parahippocampus. The plexal seg- rating neural branches at the periphery of lat- ment of the AChA starts from the inferior eral geniculate body in the plexal segment, choroidal point at choroidal fissure, courses named as capsulothalamic artery. It gives blood posteromedially at the medial choroidal plexus, supply to posterior limb (caudodorsal and ven- and ends at the choroidal glomus. It usually tral part), the retrolenticular segment (contain- supplies the plexus coordinated with LPChA in ing Meyer’s loop) of the internal capsule, the the temporal horn, but on occasion, it could tail of the caudate nucleus, and the lateral tha- feed the choroidal plexus alone in atrium, even lamic nucleus [1, 6, 7]. Medial Temporal Lobe Tumors: Surgical Anatomy and Technique 305 a b c d Fig. 4 Arterial Supply of the middle and posterior seg- MTL, and 1 splenial artery (SA) and 1 posterior hippo- ment of MTL. (a) Medial view of the uncal sulcus in campal artery supplying the posterior segment of MTL. A. another specimen. One AHPA and 1 posterior hippocam- Ch.A, anterior choroidal artery; Ant. Hippo. Parahippo. pal parahippocampal artery (PHPA), both originating A., anterior hippocampal-parahippocampal artery; Ant. from the PCA, serve to irrigate the hippocampal head and Hippo. V., anterior hippocampal vein; Ant. Inf. Temp. A., body. No UHA was found in this specimen. (b) anterior-inferior temporal artery; Ant. Long. Hippo. V., Medioinferior view of the fimbriodentate sulcus showing anterior longitudinal hippocampal vein; Ant. Parahippo. 2 AHPAs, originating from the MITA, running above the A., anterior parahippocampal artery; AHA, anterior hip- flat surface of the subiculum of the parahippocampus with pocampal artery; Basal V., basal vein; Chor. Plex., choroid a slightly curved contour. It ultimately reaches the hippo- plexus; Coll. Sulc., collateral sulcus; Entorhin. Area, ento- campal sulcus and fimbriodentate sulcus to feed the hip- rhinal area; Mam. Body, mamillary body; MHA, middle pocampal body. (c) Inferior view of another dissected hippocampal artery; Mid. Inf. Temp. A., middle-inferior MTL shows the arterial network in this sample, which is temporal artery; Parahippo. Gyrus, parahippocampal formed by 1 UHA and 1 AHPA supplying the anterior seg- gyrus; PCA, posterior cerebral artery; P. Co. A., posterior ment of MTL; 4 PHPAs supplying the middle segment of communicating artery; PHA, posterior hippocampal MTL; and 1 splenial artery (SA) originating from the artery; Post. Hippo. Parahippo. A., posterior hippocampal- posterior-inferior temporal artery, distributing into the parahippocampal artery; Post. Inf. Temp. A., posterior- posterior segment of MTL. (d) Medial view of the another inferior temporal artery; Splen. A., splenial artery; Tent. temporal lobe showing vascular network in this specimen, Notch, tentorial notch; Uncal Sulc., uncal sulcus; Unc. which is formed by 1 AHPA supplying the anterior seg- Hippo. A., uncal hippocampal artery. (With permission ment of MTL, 2 PHPAs supplying the middle segment of from Juan Carlos Fernandez-Miranda, MD) Anterior Uncal Arteries (AUA) study. The AUA normally appear in the first one- The anterior uncal arteries (AUA) originate from third of the AChA, right before it hits the lateral the AChA, ICA or MCA to the anterosuperior sur- margin of the optic tract, at a distance of 5 mm face of the uncus and irrigate the anterior uncus. (0–15 mm) on average, from the origin of the Usually, AChA generates an averagely of 1.2 (0–3) AChA. It gives blood supply to semilunar gyrus in anterior uncal arteries. The anterior uncal artery is 60% of cases, semilunar and ambient gyri in 30% not present in only 17% of cases in our previous of cases and ambient gyrus in 10% of cases. 306 Y. Xu et al. Posterior Uncal Artery (PUA) M1 wraps around the limen insula as it crosses The posterior uncal artery (PUA) originates from from internal to lateral, where it typically splits the AChA and irrigates the posteromedial uncus into two trunks. Early branches are cortical which is formed by the cisternal surface of the branches that originate from the ventromedial head of hippocampus. Usually AChA gives off side of M1 segment. Lenticulostriate arteries are 0 - 3 posterior uncal arteries (average 1.3). They the perforating branches that enter the anterior emerges normally in the middle third of the perforated substance and arise from the dorsolat- AChA, 13 mm on average (6–20 mm) distal to eral side of M1 segment (rarely from M2) [8, 9]. the origin of AChA before it arrives at the ending The irrigation is highly variable at the anterior of band of Giacomini. The PUA descends down MTL, which showed 3 differentiated patterns in the band of Giacomini and accesses the uncal sul- our previous study: anterior pattern in 41% of cus. When more than 1 PUA is present, they were cases, anteroinferior pattern in 51% of cases and dispersed to the posteromedial uncus, where they inferior pattern in 8% of cases. In the anterior send out a number of minuscule branches to pattern, the anterior uncus, especially anterior uncinate or intralimbic gyri without entering ambient gyrus is irrigated by the anterior uncal uncal sulcus. arteries (AUA). In the anteroinferior pattern, the feeding artery also descended to the inferior sur- Uncohippocampal Artery (UHA) face of MTL and supplied anterior entorhinal The uncohippocampal artery (UHA) originates area after passing the ambient gyrus, named as from PUA or AChA directly in most cases, and the same with unco-parahippocampal arteries penetrates into the uncal sulcus and is distributed in (UPHA). The arteries in the third inferior pattern, the anterior uncal sulcus, or the superior surface of which are known as the anterior parahippocam- entorhinal area which is hidden in the uncal sulcus. pal arteries (APHA), irrigated the anterior por- The entry point at uncal sulcus, in relation to the tion of the entorhinal area by reaching the inferior uncal apex, is averagely 8.9 mm (7-13 mm) poste- surface of the anterior MTL. riorly. During the hidden course in uncal sulcus, it runs serpentinely to the deepth of uncal sulcus and gives off several perforated ramies to supply the 3.3 Internal Carotid Artery (ICA) hippocampal head, uncinate gyrus superjacently and the anterior parahippocampus gyrus subja- The choroidal segment of the ICA, exactly the cently. The UHA is commenly anastomosed with section between the AChA and the bifurcation, is the AHPA at the uncal sulcus (76%) [1, 2]. intimately related to the MTL. Remarkably, these branches from ICA to MTL are present Unco-Parahippocampal Artery (UPHA) when the anterior uncal branch of the AChA or The unco-parahippocampal artery (UPHA) usu- MCA is absent, which shows a reciprocal rela- ally originates from the branches of AChA (AUA tionship between the uncal branches of the or UHA) to the inferior surface of the anterior AChA, ICA, or MCA. According to their distri- MTL and gives blood supply to the entorhinal bution, 96% of branches were AUA, and 4% area. were APHA. It’s interesting to note that the dis- tribution of the AUAs of the ICA mimicked the pattern of the AUAs of the AChA when their ori- 3.2 Middle Cerebral Artery (MCA) gin was closer to AChA than to the end segment of ICA. The distribution of the AUAs of the ICA, The M1 segment of MCA is intimately related to on the other hand, mimicked the pattern of the the MTL. The proximal part of M1 is located AUAs of the MCA when their origin was closer posteroinferiorly to the ambient gyri, superiorly to the end segment of ICA than the origin of the to anterior perforated substance. The horizonal AChA [10, 11]. Medial Temporal Lobe Tumors: Surgical Anatomy and Technique 307 3.4 Posterior Cerebral Artery and posterioinferior temporal artery (PITA). (PCA) The AITA originates from P2a in 39% of hemi- spheres or P2p in 61% of hemispheres , typi- The PCA and its branches are the main feeding cally located near the level of the posterior uncus vessels of the MTL. It has a close connection to (anterior-middle segment of MTL transition), the anterior, middle, and posterior MTL. The and the distance is always less than 1 cm to that PCA is divided into four segments based on con- level. The AITA traverses the inferior surface of stant anatomic landmarks: precommunicating anterior parahippocampus to reach rhinal sulcus, segment (P1), postcommunicating segment (P2), and in 69% of cases sends out 1–2 branches of which can be subdivided into anterior or crural anterior parahippocampal artery that vascularizes (P2a) segment and posterior or ambient (P2p) the entorhinal region and anterolateral segment, quadrigeminal segment (P3), and calca- parahippocampus. rine segment (P4). The anterior MTL is intimately related to the Anterior Hippocampal-Parahippocampal P2a segment. As it travels from the interpeduncu- Artery (AHPA) lar cistern to the crural cistern and turns at the The AHPA origins from PCA (42%), in which crus cerebri, it has a close spatial relationship P2a hold 52% and P2p hold 48%, AITA(56%), with uncal sulcus and posterior uncus. The mid- LPChA (2%). The enter point of AHPA at uncal dle segment of the MTL is related to P2p seg- sulcus is at an average of 13 mm posterior to the ment, which courses in the ambient cistern at this uncal apex and at an average of 1 mm anterior to level and lies on the medial aspect of the poste- the posterior limit of the uncus (PLU), which rior parahippocampal gyrus, then moves to the usually lies hidden underneath the anterior hip- medial margin of the parahippocampal gyrus. pocampus vein. Frequently it penetrates the pos- The posterior inferior temporal artery (PITA) and terior uncal sulcus and produces several the parieto-occipital arterial trunk (P2p) com- perforated rami to supply the posterior uncal sul- prise the most prevalent pattern of PCA proximal cus, the head, and anterior body of hippocampus. bifurcation. The AHPA is regularly anastomosed with the The P3 segment, which passes via the quadri- UHA and PHPA in the uncal sulcus (74% and geminal cistern, the splenium of corpus callo- 56%), respectively. sum, and the anteroinferior aspect of the cingulate isthmus sequentially before entering the anterior Posterior Hippocampal-Parahippocampal calcarine sulcus, is associated with the posterior Artery (PHPA) MTL. Before exiting the quadrigeminal cis- There is a large of variability of PHPA origin, tern, all branches of the inferior temporal arteries among which were PCA (33%), MITA(20%), have already been raised from PCA. The distal PITA(33%), Splenial artery (9%), AITA(5%), bifurcation of the PCA was seen in 86% of cases LPChA(2%). The PHPA travels above the hori- in our previous research , where the parieto- zonal plane of the subiculum with a liner or occipital arterial trunk divided into the calcarine slightly curved shape and provides dispersed artery and parieto-occipital artery. The branches rami to surrounding structures. It curves posteri- arising from the PCA to vascularize the MTL are orly upon reaching the hippocampal sulcus and described below. gives rise to several perforated branches into the hippocampal proper. Inferior Temporal Arteries (ITA) The group of ITAs originates from the PCA, and Lateral Posterior Choroidal Artery (LPChA) can be divided into three vessels according to the Typically, the LPChA originates from the poste- location: anteroinferior temporal arteries rior segment of the P2 with double trunks as a (AITA), middle inferior temporal artery (MITA) C-shaped trajectory. The superior trunk of 308 Y. Xu et al. LPChA generally travels in the ambient cistern to Parieto-Occipital Artery (POA) reach the choroidal fissure and feed the medial The POA is the terminal branch of PCA, which side of choroid plexus, then extends posteriorly normally travels into the parieto-occipital sulcus to the fimbria and crus of fornix and terminates at and nourishes the cuneus and precuneus. the posterolateral surface of pulvinar. The infe- rior trunk of LPChA normally reaches the Calcarine Artery (CA) fimbrio-dentate sulcus passing beneath the fim- The CA, Named according to its course in the bria, penetrating the choroidal fissure seldom, calcarine fissure, originates usually from the P3 and finally terminates at the posteromedial sur- segment of PCA. It courses deep in the fissure, face of pulvinar. The LPChA is divided into three supplies to the cuneussuperiorly and the lingual segments according to our previous research: the gyrusinferiorly. first or cisternal segment, from PCA to choroidal fissure with a length of 10.6 ± 2.5mm; the second or forniceal segment, from the penetrating site at 4 Venous Drainage choroidal fissure, exactly posterior to the inferior choroidal point with a distance of 8.2 ± 5.7mm, The basal vein of Rosenthal is the primary to the posterior choroidal fissure with a length of venous pathway that drains the MTL. It is 28.7 ± 6.8mm; and the last or pulvinar segment, divided into three segments: the first (also from the posterior choroidal fissure to pulvinar known as striate or anterior) segment; the sec- with a length of 5.9 ± 2.2mm. ond (also known as peduncular or middle) seg- ment, which is further subdivided into two Medial Posterior Choroidal Artery (MPChA) subsegments: the anterior peduncular segment The MPChA is commonly derived from the P2 and posterior peduncular segment; and the third segment of the PCA or PCA branches. The course (also known as mesencephalic or posterior) seg- of MPChA can be divided into 2 segments: cis- ment (Fig. 5). ternal and plexal segment. The cisternal segment ascends deep to PCA and gives tiny branches to the tegmentum, midbrain, pulvinar and pineal 4.1 Anterior Segment of the MTL gland. The plexal segment is formed once it pen- etrates the velum interpositum. It then feeds the The anterior segment of the MTL is composed ipsilateral choroid plexus at the roof of the third of striate segment and the anterior peduncular ventricle. It passes via the foramen of Monro and segment of the basal vein of Rosenthal. The anastamoses with branches from LPChA. striate segment of basal vein travels parallel to the anterosuperior part of uncus, while the Splenial Artery (SA) anterior peduncular segment of basal vein runs The SA, also termed as posterior pericallosal parallel to posterosuperior part of uncus. Both artery (PPA), originates from parieto-occipital veins converge at the site of the uncal apex, the branch of the PCA in quadrigeminal cistern, then anterior boundary of the crus cerebri, below runs superiorly toward the splenium of corpus the optic tract, which corresponds to the ori- callosum, enters into the callosum sulcus between gins of the peduncular vein. The striate seg- isthmus of the cingulate gyrus and the splenium ment of basal vein is typically created by the of corpus callosum. It continues to ascend to the junction of the anterior cerebral vein (ACV) roof of splenium and anastomoses with the peri- medially and the deep middle cerebral vein callosal artery. In our precious research, the SA (MCV) laterally. The inferior striate veins, produces a curved loop at medial surface of sple- olfactory, and fronto-orbital veins served as nium giving out multiple branches penetrating branches draining into MCV or ACV. the subiculum to feed the hippocampal tail in Generally, the anterior region of the uncus is 49% hemispheres. drained by anterior uncal vein or a cortical