远外侧入-路枕骨髁后管及髁后导静脉

The Posterior Condylar Canal and Posterior Condylar Emissary Vein

Department of Neurosurgery Faculty of Medicine, Saga University, Saga, Japan

As PCC and posterior condylar emissary vein coursing in the posterior part of the jugular tubercle represent good intraoperative anatomical landmarks when drilling during the lateral foramen magnum approaches, they will now be explained in more detail [23, 25, 31, 33]. The step-by-step dissection series presented in Fig. 17.5 shows the posterior and superior views of the left lateral foramen magnum, demonstrating the course of PCC. The extracranial orifice of PCC opens at the bottom of the condylar fossa just posterior to the condyle (Fig. 17.5a). With the occipital bone partially removed, PCC can be seen coursing in the posterior part of the jugular tubercle from behind (Fig. 17.5b). As HGC runs anterior to PCC, HGC is not exposed at this stage. HGC is exposed when the jugular tubercle is removed more anteriorly (Fig. 17.5c). The jugular tubercle is situated superior to HGC, and the condyle is inferior to it. On the resected surface of the jugular tubercle, PCC is not present anymore. In the superior view of the lateral foramen magnum, the intracranial orifice of PCC opens near the posterojugular ridge, which is the boundary between the distal end of the sigmoid sulcus and the jugular foramen (Fig. 17.5d). As reported in our previous study [23], the intracranial orifice of PCC can be classified into four types (Fig. 17.6). After removing the roof of PCC, its entire course, which runs in the posterior part of the jugular tubercle and opens at the condylar fossa, is visible (Fig. 17.5e). When the roof of HGC is partially removed, the canal can be seen anterior to the entire course of PCC. The canal is situated superior to the extracranial orifice of PCC and inferior to its intracranial orifice, in the so-called twisted position (Fig. 17.5f).

Fig. 17.5The posterior condylar canal (PCC) in bone. Left posterior and superior views. (a) Posteroinferior viewof the intact dry skull. The left condylar fossa is located posterior to the condyle. PCC opens at the bottom of the fossa. (b) Posterior view, with the occipital bone partially removed. The left PCC can be seen at the cutting surface. It courses in the posterior part of the jugular tubercle. (c) Posterior viewwith the posterior part of the jugular tubercle and condyle removed. The cutting surface of the left jugular tubercle and condyle is visible, but PCC is not. The jugular tubercle is superior to the hypoglossal canal (HGC) and the condyle is inferior to the canal. (d) Superior viewof the intact left lateral foramen magnum. The posterojugular ridge (Posterojug. Ridge) is situated at the boundary between the distal end of the sigmoid sulcus and the jugular foramen. PCC opens in the posteromedial wall of the jugular foramen (from Matsushima K et al. [23] with permission). (e) Superior viewof the occipital bone with opening of the roof of PCC. PCC runs posteroinferiorly from the jugular foramen to the bottom of the condylar fossa, making a slight internal curve (from Matsushima K et al. [23] with permission). (f) Posteromedial oblique view. The bone is slightly tilted to show HGC clearly. The medial half of the roof of HGC was also removed. The entire course of HGC, which is located anterior to PCC, can be seen. HGC runs almost horizontally between the jugular tubercle and occipital condyle (from Matsushima K et al. [23] with permission)。

Fig. 17.6

Illustrations showing variation in the course of the posterior condylar emissary vein (from Matsushima K et al. [23] with permission). (a) Sigmoid sinus (SS) type. The intracranial orifice of the posterior condylar canal (PCC) opens in the posterojugular ridge, which is the boundary edge between the distal end of the sigmoid sulcus and the jugular foramen (JF). The posterior condylar emissary vein (PCEV) originates from the distal end of SS. (b) Jugular bulb (JB) type. PCC opens in the medial wall of the posterior part of JF, and PCEV originates from JB. This was the most common type in our patient cohort. (c) Occipital sinus (OS) type. The large OS descends along the posterolateral edge of the foramen magnum. PCC opens in the floor of the occipital sulcus (Occipi. Sulcus) without penetrating the occipital condyle, and PCEV originates from OS before draining into JB. (d) Anterior condylar emissary vein (ACEV) type. PCEV in PCC connects to ACEV in the hypoglossal canal intracranially

The step-by-step dissection series in Fig.17.7shows the left transcondylar fossa approach combined with the transcerebellomedullary fissure approach, demonstrating how PCC and posterior condylar emissary vein are considered as intraoperative anatomical landmarks, and that the condylar fossa and the jugular tubercle are obstacles.

Fig. 17.7 The left transcondylar fossa approach combined with the transcerebellomedullary fissure approach in a step-by-step dissection of a cadaveric specimen. (a) Bony opening, as seen immediately after craniotomy. The condylar fossa is left intact and the large posterior condylar emissary vein is visible at its inferior aspect. (b) Dural opening. The condylar fossa is an obstacle. (c) After the removal of the condylar fossa and posterior part of the jugular tubercle, the operative field became wider. (d) The cerebellomedullary fissure has been opened