圖1所示。顯示屍體大腦標本後視圖的照片。圖示小腦枕下麵和小腦髓裂。圖A和B顯示一個標本，圖C和D顯示另一個。答:枕下麵位於乙狀竇和橫竇之間的下方，是寬雙側枕下開顱術中露出的麵。蚓部位於凹陷處，小腦後切骨位於兩個半球表麵之間。小腦延髓裂向上延伸至小腦和延髓之間。小葉在扁桃體之間向上延伸，並通過Magendie孔與第四腦室相通。左異食癖沿扁桃體下極下方延伸至小腦髓裂下緣，並支配部分枕下表麵。B:左扁桃體向外側收縮，小舌向內側收縮，露出第四腦室頂的下部。 The inferior portion of the roof is formed by the tela choroidea and the inferior medullary velum. The bifurcation of the PICA into the medial and lateral trunks has been retracted to show the lateral recess. Some branches of the medial trunk, which supplies the vermis, course along the uvulotonsillar space along with the vein of the cerebellomedullary fissure. C: The right tonsil has been retracted medially from the biventral lobule. The tonsils, the most prominent structures blocking access to the caudal portion of the fourth ventricle, are attached to the cerebellar hemisphere along their superolateral borders. The fissure between the tonsil and the biventral lobule is called the tonsillobiventral fissure. D: Enlarged posterior view of the same hemisphere. Both tonsils have been retracted laterally to expose the inferior medullary velum and the tela choroidea. The choroidal arteries course along the tela choroidea, from which the choroid plexus projects into the roof of the fourth ventricle. The inferior vermian surface within the posterior cerebellar incisura has a diamond shape, the upper portion of which is called the pyramid. The lower half projects downward between the tonsils and is called the uvula. The nodule is hidden deep in relation to the uvula. The medial margin of the rostral portion of the tonsils borders the tapering edges of the uvula. The strip of the vermis within the incisura is broadest at the junction of the pyramid and uvula. The right PICA bifurcates into lateral and medial trunks, which course along the uvulotonsillar space. The lateral recess, a narrow pouch formed by the union of the roof and floor, is covered caudally by the tela choroidea. A. = artery or arteries; Cer. = cerebellar or cerebello; Chor. = choroidal, Fiss. = fissure; For. = foramen; Inf. = inferior; Lat. = lateral; Med. = medial or medullary; Post. = posterior; Tons. Bivent. = tonsillobiventral; Tr. = trunk.

圖2所示。A - C:從隱身工作站獲得的屍體大腦的冠狀(A和C)和矢狀(B) MR圖像，顯示端velar連接處(A和B中黃色箭頭指示的紅點)和上外側隱窩(C中黃色箭頭指示的紅點)的位置。D和E:屍體大腦標本照片，顯示小腦枕下表麵和第四腦室下部的逐步剝離。D:左雙腹小葉收縮，可見扁桃體雙腹裂。右扁桃體經扁桃體上外側緣的扁桃體梗分開切除。小舌在扁桃體之間向下延伸，模仿口咽的解剖結構。小腦後切口內最寬的蚓狀帶是垂錐體連接處，它限製了扁桃體的側向收縮。端瓣連接處是端部與被膜的連接線。E:切除扁桃體和部分基底，露出上髓膜和上外側隱窩。下髓膜是一層薄薄的雙側神經組織，從結節內側延伸並與每個側隱窩的背緣混合，形成每個小葉的側梗。在經蚓側入路時，穿過蚓部下部的切口暴露了下麵的結節，必須切開才能進入第四腦室。 This incision through the vermis is limited by the position of the superior medullary velum, which is closely related to the anterior portion of the nodule. The superior medullary velum forms the medial part of the superior half of the roof and expands laterally and posteriorly from the aqueduct to the level of the fastigium and lateral recess. The superolateral recess, located within the fourth ventricle and lateral to the uvula and nodule, is medial to the superior cerebellar peduncles and lies anterior to the upper edge of the inferior medullary velum. Ped. = peduncle; Sup. = superior.

圖3所示。A-E:隱形磁共振圖像顯示沿第四腦室底部和頂部的解剖標誌(黃色箭頭指示的紅點)。冠狀麵(A)和矢狀麵MR圖像(B)顯示了obex的位置。矢狀麵MR圖像(C和D)顯示了頂部和導水管。矢狀麵MR圖像(E)顯示第四腦室底部及其與上髓膜和頂膜的關係。(該大腦部分與圖g所示的屍體矢狀麵幾乎位於同一水平麵上)F:小腦在中線處被切開，左半部分在斜冠狀麵上被進一步切片，以顯示扁桃體吻端極與齒狀核的關係。齒狀核似乎包裹著扁桃體。小腦上脛纖維起於齒狀核，並在小腦上脛內側上升。骨髓紋穿過地板的中部。 The vestibular area, the portion of the floor that is lateral to the median eminence and the sulcus limitans, is located at the lateral limit of the floor of the fourth ventricle. The inferior fovea is a depression in the sulcus limitans located lateral to the hypoglossal triangle. The median eminence contains the facial colliculi in its upper part and the hypoglossal and vagal triangles and the area postrema in its lower portion. The median eminence is crossed by the funiculus seperans. The trochlear nerves arise below the inferior colliculus. G: Sagittal section of a hemisphere. The full length of the floor of the fourth ventricle from the inferior edge of the aqueduct to the obex is approximately 4 cm. The roof of the fourth ventricle is a tent-shaped structure. The apex of the roof, the fastigium, is the site of the roof’s greatest height and width. The superior half of the roof expands posteriorly from the aqueduct to the level of the fastigium. This sagittal section corresponds to the Stealth MR image in panel E. CN = cranial nerve; Coll. = colliculi or colliculus; Tri. = triangle; Vest. = vestibular.

圖4所示。A - C:從隱身工作站獲得的屍體頭部的冠狀(A)，矢狀(B)和軸向(C) MR圖像，顯示了側隱窩(黃色箭頭表示的紅點)。三幅圖像上的點都是一樣的而且都來自同一具屍體。D和E:另一具屍體標本的照片顯示小腦枕下表麵的階梯式剝離。兩個扁桃體都已向上外側縮回，脈絡膜下半部的左側已打開(D)。脈絡膜叢從脈絡膜下側的室麵延伸至第四腦室。脈絡膜側向小腦下梗上方延伸，形成外側隱窩的後壁。D (E)片顯示的結構視圖。脊膜側向右側收縮，暴露出第四腦室的整個底部和導水管。第四腦室與橋小腦角相連，通過側隱窩的Luschka孔。頂的上半部在內側由上髓膜形成，外側由上小腦梗的內表麵形成。下髓膜向外側與小葉的花序梗混合，向內側與結節表麵混合。 F: The left cerebellar hemisphere, the vermis, and the medial portion of the right cerebellar hemisphere have been removed to expose the full length of the floor of the fourth ventricle. The trochlear nerves arise inferior to the inferior colliculus. The superior and inferior cerebellar peduncles face the surface of the ventricle. The median sulcus divides the floor vertically in the midline. The sulcus limitans divides each half of the floor of the fourth ventricle longitudinally into a medial strip, the median eminence, and a lateral portion, the vestibular area. The sulcus limitans is most prominent at the level of two dimples, the superior and inferior fovea. The facial colliculus is medial to the superior fovea and median eminence. The locus ceruleus, a darkened area of cells, is located at the rostral end of the sulcus limitans. G: Anterolateral view of the brainstem and petrosal surface of the cerebellum, corresponding to the area demonstrated by the Stealth MR image in panel A. The choroid plexus protrudes from the lateral recess and foramen of Luschka behind the glossopharyngeal and vagus nerves. The trigeminal nerve arises from the midpons. The abducent nerve arises in the medial portion and the facial and vestibulocochlear nerves at the lateral end of the pontomedullary sulcus. The hypoglossal nerves arise anterior to the olives and the glossopharyngeal, vagus, and accessory nerves arise posterior to the olives. The anterior inferior cerebellar artery arises at the pontine level and courses by the abducent, facial, and vestibulocochlear nerves. The right PICA arises at the level of the vertebrobasilar junction, courses in relation to the lower cranial nerves, and passes dorsally around the medulla oblongata near the lower portion of the tonsil. H: Enlarged view of the foramen of Luschka with the glossopharyngeal and vagus nerves retracted to expose the foramen and the structures forming the lateral recess. The flocculus protrudes laterally from the inferior margin of the middle cerebellar peduncle dorsal to the facial and vestibulocochlear nerves. The rhomboid lip, a sheet of neural tissue attached to the lateral margin of the floor of the fourth ventricle, has been retracted to show the choroid plexus protruding from the lateral recess and the foramen of Luschka. A.I.C.A. = anterior inferior cerebellar artery; Bas. = basilar; Mid = middle; Plex. = plexus; Sul. = sulcus; V. = vein; Vert. = vertebral.

圖5所示。A-D:屍體標本照片顯示經蟲麵進入第四腦室。小腦枕下麵(A)。最古老和最廣泛使用的第四腦室手術入路包括在枕下麵切開下蚓部。圖A (B)所示部分解剖結構的放大視圖。兩個扁桃體已向外側縮回，露出蚓部下部、錐體和小舌。經蚓部入路進入第四腦室的切口通常被描述為穿過蚓部下部(虛線)。兩種pica都繞過扁桃體的下極到達小腦髓裂的下緣。切割蚓部下部，蚓部和扁桃體橫向縮回(C)。穿過蚓部的切口暴露了下麵的結節，必須切開該結節才能暴露頂板的下部。下蚓部兩半的收縮在下蚓部的兩個收縮邊緣之間提供了大約1 - 2cm的工作空間。隨著蚓體和扁桃體的橫向收縮，可以沿著雙側PICAs的左右端慢扁桃體節段進行工作，而不犧牲血管的任何主要分支。小腦髓裂靜脈沿下髓膜橫向延伸。 Retraction of the two halves of the nodule and the opening of the tela choroidea and inferior medullary velum through a midline incision provide access to the full length of the floor (mean length 4 cm) from the aqueduct to the obex (D). The transvermian approach provides a wide exposure of the midline superior half of the roof of the fourth ventricle and the superior medullary velum. E–H: Stealth MR images of the transvermian dissection demonstrating the superior, inferior, and lateral limits of exposure (red dots indicated by yellow arrows). The superior limit of the transvermian exposure is at the inferior edge of the aqueduct (E). The inferior limit of the transvermian exposure is at the obex (F) and the right and left lateral limits are at the level of the striae medullaris (G and H). The medial edge of the vestibular area is the lateral limit of exposure. I and J: Sagittal (I) and coronal (J) Stealth MR images obtained during the dissection, demonstrating the trajectory of the transvermian approach (yellow rectangles leading to red dots). The fastigium and the inferior portion of the superior medullary velum are the main anatomical structures that limit the working angle to the rostral one fourth of the floor of the fourth ventricle during the transvermian approach and this is demonstrated in the sagittal plane.

圖6所示。屍體大腦標本照片顯示端瓣入路至第四腦室。答:暴露扁桃體和雙腹小葉後，打開兩側的懸垂扁桃體和髓扁桃體間隙。B:扁桃體已向外側縮回，暴露右側懸垂扁桃體間隙，特別注意保存異食癖及其進入內側和外側主幹的分支。異食癖分岔位於懸垂扁桃體空間下端附近，靠近端瓣連接處，約30%的標本中有異食癖分岔。C:右扁桃體向上外側收縮，小舌向內側收縮，露出右小舌扁桃體空間。將直角神經鉤的尖端置於上外側隱窩的下髓膜下。鉤的尖端可以透過薄的下髓膜看到。D:小舌已向超內側收縮，右扁桃體向超外側收縮，以達到最大程度的顯像。PICA分支已向外側縮回，而不犧牲血管的任何分支。 If the PICA bifurcation is present at the uvulotonsillar space along the site of the telovelar incision, it is easier to retract it laterally before creating an incision along the tela than to retract it medially in most hemispheres. The incision along the tela choroidea in the right half of the roof has been extended to the telovelar junction. The entire floor of the fourth ventricle from the obex to the aqueduct has been exposed. E: The right half of the inferior medullary velum has been divided to expose the superolateral recess and maximize the exposure along the medial superior half of the roof and superior cerebellar peduncle. Opening the inferior medullary velum increases the exposure of the lower portion of the superior medullary velum near the fastigium. The vein of the cerebellomedullary fissure, which crosses the upper end of the inferior medullary velum, has been preserved. Retracting the right tonsil superolaterally provides access to the lateral recess and exposes the rhomboid lip. Hem. = hemispherical; Ver. = vermian.

圖7所示。Telovelar方法。矢狀位、冠狀位和軸向隱身MR圖像的手術暴露極限(紅點由黃色箭頭表示)。A:沿著第四腦室底部暴露的上限值是導水管。B:端瓣入路提供了從導水管到腹壁的第四腦室底部的整個長度，這是暴露的下極限。C和D:第四腦室底部暴露的外側界限位於髓紋水平，靠近外側隱窩的內側邊緣。E:將扁桃體上外側抬高，暴露出外側隱窩的全長和外側隱窩下外側端的Luschka孔。F:上外側暴露極限為上外側隱窩，隻有切開下髓膜才能暴露。G和H:在解剖過程中獲得的冠狀麵和軸向隱身MR圖像顯示了端瓣入路的軌跡(黃色矩形通向紅點)。在端瓣入路中，第四腦室從中線穿過懸垂扁桃體間隙，通過打開端脈絡膜和小舌外側的下髓膜進入。

圖8所示。屍體大腦標本的照片，顯示在逐步解剖中橫向和端velar暴露的比較。A和B:橫向入路。穿過蚓部下部的橫切切口暴露了底層的結節，必須切開才能進入第四腦室(A)。穿過蚓部的切口受限於位於結節前上邊緣的上髓膜的位置。下蚓部成對半部分的收縮提供了切口蚓部邊緣之間約1至2厘米寬的暴露。放大視圖(B)。隨著脈絡膜尾部和下髓質膜通過橫貫切口的打開，從導水管到腹壁的完整長度(平均長度4厘米)可以暴露出來。上髓膜限製了暴露的上部。經蟲側入路可以更好地暴露第四腦室頂部上半部的中線部分。橫斷麵暴露的外側界限延伸到髓紋和前庭區域的內側邊緣。氟:Telovelar方法。 The tonsils have been retracted superolaterally to expose the tela choroidea, inferior medullary velum, and both lateral recesses (C). The lateral limit of the exposure achieved is the foramen of Luschka, where the choroid plexus protrudes behind the glossopharyngeal and vagus nerves. The uvula has been retracted medially and the right tonsil laterally, and the tela and inferior medullary velum have been opened to expose the entire length of the floor of the ventricle (D). The aqueduct and the obex are the superior and inferior limits of the exposure along the floor. View of structures shown in panel D (E). The lateral limits of the exposure along the floor of the fourth ventricle are similar to those provided by the transvermian approach and located at the level of the striae medullaris, near the medial edge of the lateral recesses. Incising the inferior medullary velum provides access to the superolateral recess and most of the midline superior half of the roof of the fourth ventricle formed by the the superior medullary velum. View of another specimen (F). Both tonsils have been elevated to expose the full length of the lateral recesses. The rhomboid lip at the lateral end of the lateral recess has been exposed on the right side. The left PICA bifurcates into medial and lateral trunks at the inferior end of the uvulotonsillar space.

圖9所示。疊加在屍體大腦切片照片上的圖表，展示了沿著第四腦室底部的橫貫入路和端瓣入路的手術角度比較。沿第四腦室底矢狀麵測量角度。角的頂點被放置在沿著第四腦室底部的三個位置:渡槽，從obex測量到渡槽下邊界的距離的中點(50%點)，以及該距離的75%點。A:矢狀麵顯示小腦枕下表麵蚓部。蚓部突出的部分是去裂體(橙色)、小葉(紫色)、塊莖(藍色)、錐體(黃色)、小舌(綠色)和結節(淺紅色)。頂脊是第四腦室頂的頂端，它將腦室頂分為上、下兩部分，位於中點和75%點之間，接近矢狀麵中段。切口的上限(虛線)通過小舌、錐體、塊莖和小葉的下部延伸到頂部，但沒有進入上髓膜的下邊緣。B:經腹膜入路和端瓣入路可以很好地暴露從腹壁到導水管的第四腦室的整個底部。渡槽測得的橫斷麵和端麵入路的平均手術角度分別為38′(角A)和30′(角B)。 In the sagittal plane the exposure gained at the aqueduct when the telovelar approach is used is shaded green. The mean difference between the operative angles of the two approaches at the aqueduct did not exceed 8 ̊ in favor of the transvermian approach (shaded light red). In both the transvermian and telovelar approaches, the operative angle of approach was limited by the superior medullary velum in the sagittal plane. The limitation was most significant when exposing the rostral end of the fourth ventricle near the aqueduct. The working angle decreases when moving away from the midline. In the telovelar approach, the fourth ventricle is approached off the midline, which accounts in part for the decrease in operative angle. The uvulopyramidal junction, the broadest strip of vermis within the posterior incisural space, limited the lateral and medial retractions of the tonsil and the uvula at the uvulotonsillar space, respectively. C: The mean operative angles of the transvermian and telovelar approaches measured at the 75% point were 72 ̊ (Angle A) and 67 ̊ (Angle B), respectively. In the sagittal plane, the exposure at the 75% point for the telovelar approach is shaded green. The mean difference in the working angle gained through the transvermian approach at the 75% point is shaded light red. The lower edge of the superior medullary velum limited the working angle at the 75% point in both approaches and the uvulopyramidal junction accounts for the decrease in the operative angle in the telovelar approach. D: The operative angles of the transvermian and telovelar approaches measured at the midpoint along the length of the floor of the fourth ventricle were identical, 84 ̊ (Angle A). At the midpoint, the working angle gained in the sagittal plane is shaded blue. At the midpoint along the floor of the fourth ventricle, the working angle increased dramatically compared with the working angle at the aqueduct.