The Dorello canal: historical development, controversies in microsurgical anatomy, and clinical implications.

Interest in studying the anatomy of the abducent nerve arose from early clinical experience with abducent palsy seen in middle ear infection. Primo Dorello, an Italian anatomist working in Rome in the early 1900s, studied the anatomy of the petroclival region to formulate his own explanation of this pathological entity. His work led to his being credited with the discovery of the canal that bears his name, although this structure had been described 50 years previously by Wenzel Leopold Gruber. Renewed interest in the anatomy of this region arose due to advances in surgical approaches to tumors of the petroclival region and the need to explain the abducent palsies seen in trauma, intracranial hypotension, and aneurysms. The advent of the surgical microscope has allowed more detailed anatomical studies, and numerous articles have been published in the last 2 decades. The current article highlights the historical development of the study of the Dorello canal. A review of the anatomical studies of this structure is provided, followed by a brief overview of clinical considerations.

Dorello canal revisited: an observation that potentially explains the frequency of abducens nerve injury after head injury.

OBJECTIVE: The abducens nerve is frequently injured after head trauma and some investigators have attributed this to its long intracranial course. The present study aimed to elucidate an additional mechanism to explain this phenomenon. METHODS: Twelve fresh adult cadavers underwent dissection of Dorello canal using standard microsurgical techniques. In addition, traction was applied to the nerve at its entrance into this canal before and after transection of Gruber ligament to observe for movement. RESULTS: In all specimens, a secondary tunnel (i.e., tube within a tube) was found within Dorello canal that exclusively contained the abducens nerve. This structure rigidly fixated the abducens nerve as it traversed Dorello canal, thereby not allowing any movement. Transection of Gruber ligament did not detach the nerve, but after release of the inner tube, the nerve was easily mobilized. CONCLUSIONS: Rigid tethering of the abducens nerve with a second tube within Dorello canal affords this nerve no ability for movement with motion of the brainstem. We hypothesize that this finding is a main factor in the high incidence of abducens nerve injury after head trauma.

Development of cranial nerve palsy shortly after endosaccular embolization for asymptomatic cerebral aneurysm: report of two cases and literature review.

CLINICAL DESCRIPTION: We report two cases of asymptomatic cerebral aneurysm in which cranial nerve palsy (CNP) developed shortly after symbolization. The CNP occurred immediately in case 1, but case 2 showed the CNP 30 h after symbolization. Although both aneurysms had increased in size on follow-up angiography, case 2 who showed dome re canalization resulted in progressive CNP deterioration. CONCLUSION: These findings suggest that the CNP may result not only from mechanical compression by coils but also from inflammation induced by perpendicular thrombosis, and that the prognosis of the CNP may be influenced by dome re canalization. This complication should be kept in mind in treatment for asymptomatic aneurysms adjacent to the cranial nerves.

Traumatic retroclival epidural hematoma in a child: case report.

An 11-year-old girl presented with a very rare traumatic retroclival epidural hematoma manifesting as bilateral abducens nerve palsy, deviation of the uvula to the left, and weakened movement of tongue, which developed after a motor vehicle accident. The patient was treated conservatively and showed good outcome. Retroclival hematoma is a mainly pediatric entity usually associated with ligamentous injury at the craniocervical junction, and can be treated conservatively with good outcome.

A chronically implantable device for the controlled delivery of substances, and stimulation and recording of activity in severed nerves.

We describe the use of an implantable device for peripheral nerves that allows chronic simultaneous delivery of small volumes of solution, recording of both field and multiunit potentials, and electrical stimulation. This custom-made multifunctional device was attached to the cut end of the abducens (VIth) nerve for stimulation, recording and injection purposes. Our device consists of a polyethylene chamber with two electrodes that can be used for stimulation and recording and two Teflon tubes that serve as inlet and outlet for administering chemicals to the nerve fitted inside. Since the device is implanted in a retro-orbital position, we herein will refer to it as an intraorbitary device (IOD). The applicability of the IOD is demonstrated with an electrophysiological and anatomical account of the properties of the abducens nerve. Furthermore, it is shown that certain neuronal discharge properties can be inferred from the nerve recordings. The IOD can also be efficiently used for the delivery of small volume of pharmacological substances or conventional retrograde markers.

Bilateral traumatic facial paralysis associated with unilateral abducens palsy: a case report.

Bilateral traumatic facial paralysis is a very rare clinical condition. Abducens palsy, associated with bilateral traumatic paralysis, is even rarer and has not been well described in the literature. In this report, a 24-year-old male, who developed immediate bilateral facial and right abducens paralyses following a motor vehicle accident, is presented. The patient was referred for neurotologic evaluation 22 days after the injury. Electroneurography (ENoG) demonstrated 100 per cent degeneration at the first examination and, correspondingly, electromyography showed no regeneration potentials. Using high-resolution computed tomography (HRCT), a longitudinal fracture on the right and a mixed-type fracture on the left were identified. The patient had good cochlear reserve on both sides. The decision for surgery was based not on ENoG, because of the delayed referral of the patient, but on the HRCT, which showed clear fracture lines on both sides. The middle cranial fossa approach for decompression of the right facial nerve was performed on the 55th day following the trauma, and a combined procedure using the middle cranial fossa and transmastoid approaches was applied for decompression of the left facial nerve on the 75th day following the trauma. On the right, there was dense fibrosis surrounding the geniculate ganglion and the proximal tympanic segment whereas, on the left, bone fragments impinging on the geniculate ganglion, dense fibrosis surrounding the geniculate ganglion, and a less extensive fibrotic tissue surrounding the pyramidal segment were encountered. There were no complications or hearing deterioration. At the one-year follow up, the patient had House-Brackmann (HB) grade 1 recovery on the right, and HB grade 2 recovery on the left side, and the abducens palsy regressed spontaneously. The middle cranial fossa approach and its combinations can be performed safely in bilateral temporal bone fractures as labyrinthine sparing procedures if done on separate occasions.

The mechanism of injury of the abducens nerve in severe head trauma: a postmortem study.

The aim of this study is to investigate the mechanism of injury of abducens nerve at petroclival region in severe head trauma. Twenty specimens provided from 10 autopsied cases due to severe head trauma were investigated macroscopically and histopathogically. The slices of the abducens nerve taken consecutively along its course at petroclival region were stained with Hematoxylline-Eosin and evaluated under light microscope. In addition, coexisting cervical injuries in these cases were assessed macroscopically. Edema and perineural hemorrhagia of abducens nerve were identified in all cases. Nerve injury was found more exaggerated at the sites of dural entry point and petrous apex than any other parts of the abducens nerve. Furthermore, microscopically, also remarkable perineural hemorrhage of the abducens nerve was observed at the site of its anastomoses with the sympathetic plexus on the lateral wall of the internal carotid artery (ICA). Abducens nerve is injured at the sites of dural entry point, petrous apex and lateral wall of the ICA, directly proportional with the severity of the trauma. This finding is also significant in verification of the severe head trauma.