Typical and atypical neurovascular relations of the trigeminal nerve in the cerebellopontine angle: an anatomical study

Abstract

The aim of the present study was to anatomically evaluate in adults the neurovascular trigeminal relations in the cerebellopontine angle (CPA), from a morphological and topographical perspective and thus to improve, detail and debate the pre-existing information, with educational and surgical implications. For the present anatomical study we performed bilateral dissections on 20 human adult skull bases, in formalin-fixed cadavers, at the level of the cerebellopontine angle, using the anatomical superior approach; we also studied 20 additional drawn specimens-cerebellum and brainstems, from autopsied cadavers, in order to better document the vasculature at the trigeminal root entry zone (REZ). The most constant but not exclusive neurovascular relations of the trigeminal nerves were those with the superior cerebellar artery (SCA) and the superior petrosal vein (the petrosal vein of Dandy). The regular possibility for the SCA to appear divided into a medial and a lateral branch and these to represent individual trigeminal relations at the level of the pontine cistern or REZ must not be neglected. The petrosal vein tributaries can also represent superior, inferior, or interradicular trigeminal relations. Arterioles emerging from the SCA or the anterior inferior cerebellar artery (AICA) represented trigeminal relations either at the REZ or were coursing between the trigeminal roots. A dissected specimen presented a radicular trigeminal artery emerging from the basilar artery and entering the trigeminal cavum inferior to the nerve. Another specimen presented two bony lamellae superior to the trigeminal nerve at the entrance in the trigeminal cavum-these lamellae were embedded within the lateral border of tentorium cerebelli and the posterior petroclinoid ligament. So we bring here an evidence-based support extremely useful not only for specialists dealing with this area but also for educational purposes. It appears important not only to consider the typical anatomy at this level but also to take into account the atypical and hardly predictable morphologies that may alter the diagnoses and the specific surgical procedures.

Bilateral Extensive Ossification of the Posterior Petroclinoid Ligament: An Anatomical Case Report and Literature Review

“…The lamellae were located above the trigeminal nerve at the entrance to Meckel's cave. 17 Tubbs et al, in turn, based on observations on a macerated skull, reported the presence of bone formation within the proximal superior aspect of Meckel's cave, forming "a bony foramen for the proximal trigeminal nerve." 18 However, ossifications of the petrosphenoid ligament should be differentiated from the os suprapetrosum (described first by Meckel in 1748), a heterotropic bony formation located on the anterosuperior surface of the petrous bone near its apex.…”

“…18 However, ossifications of the petrosphenoid ligament should be differentiated from the os suprapetrosum (described first by Meckel in 1748), a heterotropic bony formation located on the anterosuperior surface of the petrous bone near its apex. 13,17,25 It was hypothesized that the posterior petroclinoid dural fold may completely ossify in adults, leading to a narrowing of the trigeminal porus and compression of the trigeminal nerve. 8,11,18,26 Hence knowledge of the anatomical characteristics of both the dural entrance to Meckel's cave and the dural sheath of the trigeminal nerve are important from a clinical point of view.…”

“…1,12 Ossifications of petroclinoid ligaments are rarely described in anatomical literature, 7,8 with most descriptions of such findings based on radiologic studies. [13][14][15][16] So far, only Kimball et al, 4 Perumal and Gayathri, 11 and Rusu et al 17 have provided observations of ossification of the posterior petroclinoid dural folds on wet specimens. However, these authors focused mainly on the significance of a completely ossified posterior petroclinoid dural fold as a factor potentially relating to trigeminal neuralgia.…”

Endoscopically Assisted Exoscopic Surgery for Microvascular Decompression of the Trigeminal Nerve with Intraoperative Use of Indocyanine Green

“…Klun and colleagues [20], in a cadaver study of 65 heads, described the frequency of occurrence of variants of the trigeminal nerve root arterial compression, where in 53.8% the cause of compression was the SCA, in 25.6% the AICA, in 20.6% the pontine branches of the basilar artery. In turn, Rusu and co-authors [21] in their study noted the possibility of division of the SCA into medial and lateral branches, and also demonstrated options for the contact of the branches of the SCA and AICA to the trigeminal nerve root, or transient passage between the roots of the trigeminal nerve. Fu et al [22] in 2015 described a clinical case of a rare cause of trigeminal neuralgia resulting from the primitive trigeminal artery, whereas Shulev et al [23] described in their work NLE caused by vertebrobasilar dolichoectasia.…”

Concomitant completely ossified trigeminal pore and Dorello’s canal

“…Such ossified PPCLs transform the osteofibrous trigeminal pore into a bony foramen [2] that is occasionally found in dry skulls [7]. Bony lamellae within the tentorial border and the PPCS were found in close contact with the oculomotor, trochlear, trigeminal and abducens nerves [5]. According to Bergman, Afifi and Miyauchi, "A bar of bone in the dura over the trigeminal nerve has been interpreted as a vestige of the primitive cranial wall as present in reptilia" [1].…”