Enlargement of Dorello's Canal as a Novel Radiographic Marker of Idiopathic Intracranial Hypertension

Objectives The objective of this study is to compare the visibility and size of Dorello's canal (DC) on magnetic resonance imaging between patients with idiopathic intracranial hypertension (IIH) and control patients, for its evaluation as a potential novel marker for chronic increased intracranial pressure (ICP). Design Retrospective blinded case–control study. Setting Tertiary care academic center. Participants Fourteen patients with spontaneous cerebrospinal fluid (CSF) rhinorrhea and diagnosed IIH, as well as an equal number of age and gender-matched controls. Main Outcome Measures Radiographic presence or absence of visible CSF sleeve within DC as well as CSF sleeve width when present. Results Following review of 28 IIH canals and 28 control canals, IIH patients were significantly more likely to have a visible CSF sleeve within DC and to have a wider measured medial entrance to DC (p < 0.001). Conclusion Identification of CSF evagination into DC may serve as a reliable marker for increased ICP in the IIH population. This finding should be considered in the future as paradigms for diagnosis of IIH continue to evolve.

Recurrent abducens nerve palsy and hypophosphatasia syndrome

A 47-year-old woman presented with six episodes of horizontal binocular double vision over a 2-year period. CT imaging was significant for extensive dural calcification in the spine and calcification of the skull base, likely involving Dorello’s canal. Biochemical testing revealed a persistently low alkaline phosphatase level. Recurrent nerve palsy may possibly be induced by mechanical compression of the sixth cranial nerve in Dorello’s canal from calcification due to hypophosphatasia syndrome.

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

Background The posterior petroclinoid dural fold (commonly referred to as a ligament) forms the roof of the trigeminal porus and the roof of the petroclival venous confluence. It lies in close proximity to the oculomotor nerve that crosses it. Due to the low availability of research material, only a few cadaveric studies have been conducted on the microsurgical anatomy of the petroclinoid ligament in cases of its ossification. Thus our report complements earlier studies and provides detailed data on the spatial relationships between the ossified posterior petroclinoid ligament and the trigeminal, oculomotor, and abducens nerves, with special attention to the topographical relationships within the petroclival venous confluence and Dorello's canal. Case Description Bilateral massive ossification of the posterior petroclinoid ligament was observed during the dissection of a 76-year-old female cadaver. The presence of an osseous bridge over the trigeminal notch was also detected on the left side. No narrowing of the space occupied by the petroclival venous confluence was observed. However, the dural sheath of the oculomotor nerve was fixed much more than usual. Conclusions Because the ossification of the posterior petroclinoid ligament may be considered a factor influencing diagnostic and surgical procedures, neurosurgeons and neuroradiologists should be aware of this variation. Ossification of the posterior petroclinoid ligament may also potentially result in greater susceptibility of the oculomotor nerve to injury.

Isolated abducens nerve palsy associated with subarachnoid hemorrhage: a localizing sign of ruptured posterior inferior cerebellar artery aneurysms

OBJECTIVECompressive cranial nerve syndromes can be useful bedside clues to the diagnosis of an enlarging intracranial aneurysm and can also guide subsequent evaluation, as with an acute oculomotor nerve (cranial nerve [CN] III) palsy that is presumed to be a posterior communicating artery aneurysm and a surgical emergency until proven otherwise. The CN VI has a short cisternal segment from the pontomedullary sulcus to Dorello’s canal, remote from most PICA aneurysms but in the hemodynamic pathway of a rupturing PICA aneurysm that projects toward Dorello’s canal. The authors describe a cranial nerve syndrome for posterior inferior cerebellar artery (PICA) aneurysms that associates subarachnoid hemorrhage (SAH) and an isolated abducens nerve (CN VI) palsy.METHODSClinical and radiological data from 106 surgical patients with PICA aneurysms (66 ruptured and 40 unruptured) were retrospectively reviewed. Data from a group of 174 patients with other aneurysmal SAH (aSAH) were analyzed in a similar manner to control for nonspecific effects of SAH. Univariate statistical analysis compared incidence and risk factors associated with CN VI palsy in subarachnoid hemorrhage.RESULTSOverall, 13 (4.6%) of 280 patients had CN VI palsy at presentation, and all of them had ruptured aneurysms (representing 13 [5.4%] of the 240 cases of ruptured aneurysms). CN VI palsies were observed in 12 patients with ruptured PICA aneurysms (12/66 [18.1%]) and 1 patient with other aSAH (1/174 [0.1%], p < 0.0001). PICA aneurysm location in ruptured aneurysms was an independent predictor for CN VI palsy on multivariate analysis (p = 0.001). PICA aneurysm size was not significantly different in patients with or without CN VI palsy (average size 4.4 mm and 5.2 mm, respectively). Within the PICA aneurysm cohort, modified Fisher grade (p = 0.011) and presence of a thick cisternal SAH (modified Fisher Grades 3 and 4) (p = 0.003) were predictors of CN VI palsy. In all patients with ruptured PICA aneurysms and CN VI palsy, dome projection and presumed direction of rupture were directed toward the ipsilateral and/or contralateral Dorello’s canal, in agreement with laterality of the CN palsy. In patients with bilateral CN VI palsies, a medial projection with extensive subarachnoid blood was observed near bilateral canals.CONCLUSIONSThis study establishes a localizing connection between an isolated CN VI palsy, SAH, and an underlying ruptured PICA aneurysm. CN VI palsy is an important clinical sign in aSAH and when present on initial clinical presentation may be assumed to be due to ruptured PICA aneurysms until proven otherwise. The deficit may be ipsilateral, contralateral, or bilateral and is determined by the direction of the aneurysm dome projection and extent of subarachnoid bleeding toward Dorello’s canal, rather than by direct compression.

Microsurgical Resection of a Meningioma at the Entrance of Dorello's Canal Causing VI Cranial Nerve Compression: 2-Dimensional Operative Video

We describe the case of a 73-yr-old female patient with a 2-yr history of diplopia that has progressively become worse. Physical examination revealed a right VI cranial nerve (CN) palsy. Magnetic resonance imaging and angiography showed a dolichoectatic basilar artery near the VI CN. A suboccipital craniectomy was performed, initially with the intention to perform a microvascular decompression; however, a red mass was encountered at the entrance of the right Dorello's canal that was compressing the VI CN. Complete resection of the lesion was done and decompression of the nerve was accomplished. In the following video illustration, we narrate this operative case and highlight the nuances of this approach. Patient consent was obtained for the submission of the video to this journal.

Gruber, Gradenigo, Dorello, and Vail: key personalities in the historical evolution and modern-day understanding of Dorello’s canal

A century ago an ambitious young anatomist in Rome, Primo Dorello, who sought to understand the cause of abducent nerve palsy that often occurred in patients with severe middle ear infections, conducted intricate studies on the intracranial course of the nerve. In his findings, he identified that the abducent nerve passes through a narrow sinus near the apex of the petrous bone, which formed an osteofibrous canal. Dorello suggested that in this enclosed region the abducent nerve may be particularly vulnerable to compression due to the vascular edema accompanying the infection. Although his work was widely appreciated, it was not well received by all. Interestingly, Giuseppe Gradenigo, one of the most prominent Italian otologists of the early 20th century, who was known for his work on a triad of symptoms (Gradenigo’s syndrome) that accompanies petrous apicitis, a result of severe middle ear infections, was obstinate in his criticism of Dorello’s findings. Thus a scientific duel began, with a series of correspondence between these two academics—one who was relatively new to the otological community (Dorello) and one who was well reputed in that community (Gradenigo). The disagreement ultimately ebbed in 1909, when Dorello published a report in response to Gradenigo’s criticisms and convinced Gradenigo to change his views. Today Dorello’s canal is widely recognized as a key landmark in skull base surgery of the petroclival region and holds clinical significance due to its relation to the abducent nerve and surrounding vascular structures. Yet, although academics such as Dorello and Gradenigo are recognized for their work on the canal, it is important not to forget the others throughout history who have contributed to the modern-day understanding of this anatomical structure. In fact, although the level of anatomical detail found in Dorello’s work was previously unmatched, the first description of the canal was made by the experienced Austrian anatomist Wenzel Leopold Gruber in 1859, almost 50 years prior to Dorello’s landmark publication. Another critical figure in building the understanding of Dorello’s canal was Harris Holmes Vail, a young otolaryngologist from Harvard Medical School, who in 1922 became the first person to describe Dorello’s canal in the English language. Vail conducted his own detailed anatomical studies on cadavers, and his publication not only reaffirmed Dorello’s findings but also immortalized the eponym used today—“Dorello’s canal.” In this article the authors review the life and contributions of Gruber, Dorello, Gradenigo, and Vail, four men who played a critical role in the discovery of Dorello’s canal and paved the way toward the current understanding of the canal as a key clinical and surgical entity.