Dorello's Canal Research Articles

Meckel's Cave Tumors

Literature on tumors originating from Meckel's cave (MC) and their surgical treatment are scarce. We present 37 cases of tumors originating from MC, the largest single-institution series reported thus far, and discuss the ideal surgical methods for each tumor type in relation to the normal and pathological anatomy of MC. We studied 37 cases of surgery for tumors in MC (26 schwannomas, 7 meningiomas, 2 epidermoids, 1 hemangiopericytoma, and 1 dermoid) performed at our institution between 1986 and 2008. We excluded cases of large tumors of unknown origin, especially meningiomas. Surgery for tumors in MC was performed via 2 approaches: anterolateral interdural access (Dolenc's) approach and posterior access via the anterior petrosal approach (APA). The Dolenc approach was useful for parasellar tumors, especially schwannomas, because it resulted in minimal damage to the temporal lobe and adjacent cranial nerves. The APA was useful for dumbbell-shaped tumors extending into the posterior fossa. Tumors of nonmeningeal origin (schwannomas, epidermoids, and dermoids) were safely resected, with no postoperative complications except facial hypesthesia. However, incidence of postsurgical paresthesia and abducens palsy were higher in meningioma and hemangiopericytoma, because of invasion into the Gasserian ganglion, the cavernous sinus (CS), or Dorello's canal. An understanding of meningeal structure around MC enhances the radicality of tumor resection and helps minimize damage to adjacent structures. However, meningiomas and hemangiopericytomas occurring in MC, which can infiltrate into the CS, should be treated by both surgery and radiosurgery to minimize postoperative complications.

A New Look at an Old Canal

Attempts to explain abducens vulnerability have centered around the petroclival segment of its pathway in the skull base, in particular, its relations to the Dorello's canal and the petrosphenoidal ligament of Grüber. This study aims to contribute to the definition of the Dorello's canal and to the understanding of abducens vulnerability from an evolutionary perspective. The petroclival region and the Dorello's canal in particular were examined in a sample of 86 primate skulls. The sample contains 20 Pan troglodytes (common chimpanzee), 35 Gorilla gorilla, 20 Pongo pygmaeus (orangoutan), and 11 Hylobates moloch (gibbon) skulls. Distance between the petrous apex and tip of the posterior clinoid process was measured using a 10-mm scale that was inserted into the endocranium. Complete absence of the Grüber ligament and an uninterrupted osseous circumference of the Dorello's canal (foramen) was demonstrated in all nonhuman primate species. Whatever the reason for the morphological difference between the human and ape Dorello's canal, it is without a doubt suggestive of the source of vulnerability of the abducens nerve, as the ligament of Grüber, unique to the human configuration, renders the contents of the Dorello's canal susceptible to compression against the cranial base.

Microsurgical anatomy of the medial tentorial artery of Bernasconi–Cassinari

In the current literature, there is a lack of detailed map of the origin, course and relationships of the medial tentorial artery (MTA) of Bernasconi-Cassinari often implicated in various diseases such as dural arteriovenous fistulas of the cranial base, stenotic lesions of the ICA, saccular infraclinoid intracavernous aneurysms and tentorial meningiomas. Using a colored silicone mix preparation, ten cranial bases were examined using ×3 to ×40 magnification of the surgical microscope. The MTA arose as a single branch in 95% of cases from the MHT at the level of the C4 segment of the internal carotid artery. The average length of the MTA was 21.7mm (range 20.0-23.4mm). The average diameter of the MTA was 0.53mm (range 0.49-0.60mm).The MTA passed just below the lower dural ring detached from the lower margin of the anterior clinoid process. During its course, the MTA drop over the intracavernous segment of the abducens nerve twisted at its exit from the Dorello's canal and overlay the trochlear into the thickness of the free margin of the tentorium cerebelli. Vascular relationships of the MTA were venous trabeculation of the cavernous sinus, basilar plexus and branches of the inferolateral trunk. The MTA sent two terminal branches: one medial rectilinear, which pursued the initial dorsal course, and the other shorter with a lateral course, which disappeared into the lateral wall of the cavernous sinus. The medial branch of the MTA curved laterally, ramifying within the free edge of the tentorium cerebelli and anastomosing along the base of the dorsal part of the falx. The implications of these anatomic findings for surgery or endovascular procedure are reviewed and discussed.

THREE-DIMENSIONAL AND 2-DIMENSIONAL ENDOSCOPIC EXPOSURE OF MIDLINE CRANIAL BASE TARGETS USING EXPANDED ENDONASAL AND TRANSCRANIAL APPROACHES

Endoscopic endonasal approaches provide an access method to the midline cranial base. To integrate these approaches into neurosurgical practice, the extent of their anatomic exposure must be compared with that provided by more traditional transcranial approaches. Ten fresh cadaver heads were studied. Both endonasal and transcranial approaches to the midline cranial base were performed. The midline cranial base was divided into several areas, and the relative exposure provided by each approach was described and presented in both 2-dimensional and 3-dimensional images. Limitations and advantages of each approach are discussed. The endonasal approaches achieved a direct and wide exposure of the midline extracranial and intracranial cranial base anatomy. The main lateral limitations of the endonasal approaches were the optic nerves, lateral cavernous sinus, vidian nerve, internal carotid artery, abducens nerve in Dorello's canal, jugular tubercle, and hypoglossal canals. Limitations of the transcranial approaches were the neurovascular structures which lie in the operative corridor and create narrow working spaces. The endonasal approaches achieve a direct and wide exposure of the midline cranial base bilaterally. Lateral exposure, beyond the cranial nerves and carotid artery, are challenging. Transcranial approaches are limited by the narrow corridors provided by the cranial nerves, and they do not visualize the contralateral paramedian cranial base very well. Three-dimensional endoscopes augment the spatial orientation and may improve patient safety and the learning curve for endoscopic approaches to the midline cranial base.

QUANTITATIVE COMPARISON OF KAWASE'S APPROACH VERSUS THE RETROSIGMOID APPROACH

Few quantitative data are available to describe Kawase's exposure of the posterior fossa. We used a cadaveric model to compare Kawase's and the retrosigmoid approach to the petroclival region. Eighteen cadaveric specimens were dissected and analyzed (6 retrosigmoid, 6 Kawase's, and 6 retrosigmoid intradural suprameatal approaches). Clival and brainstem working areas and surgical freedom were measured. The retrosigmoid approach provided a significantly larger clival and brainstem working area than Kawase's approach. Surgical freedom at the trigeminal root entry zone, origin of the anterior inferior cerebellar artery, and Dorello's canal was equivalent across approaches. Kawase's approach provided the most surgical freedom at the trigeminal porus. However, the addition of a suprameatal extension significantly improved the surgical freedom provided by the retrosigmoid approach. The retrosigmoid approach is a powerful approach to lesions of the cerebellopontine angle and ventral brainstem. Lesions involving the trigeminal porus and Meckel's cave can be approached through Kawase's approach or a suprameatal extension of the retrosigmoid approach. Kawase's approach is best suited for accessing middle fossa lesions with smaller petroclival components located above the internal auditory canal.

Anatomy of the petrosphenoidal and petrolingual ligaments at the petrous apex

The petrous apex is a complex area surrounded by the cavernous sinus, Dorello's canal and Meckel's cave. The petrosphenoidal ligament (PSL) and the petrolingual ligament (PLL) are important structures located in the region. These two ligaments were examined under a surgical microscope in 10 specimens of five adult cadaveric heads fixed in formalin. They were found to span from the petrous apex to the posterior clinoid process, and the lingula of the sphenoid bone, respectively. The dural sleeve of the abducens nerve, the dorsal meningeal artery or its medial branch, and the venous blood space were located below the PSL in all specimens, and the petrous or sphenoidal insertion of the PSL varied in five specimens. The PLL invariably surrounded part of the dorsal and lateral walls of the lacerum segment of the internal carotid artery (ICA), just under the anteroinferior portion of the anteromedial wall of Meckel's cave in all specimens. The PSL and PLL are valuable anatomical landmarks for identifying the ICA and the nerves in this region. A thorough understanding of the relationship of the two ligaments with neurovascular structures is a prerequisite for surgery in and around the petrous apex.

Gradenigo Syndrome

Gradenigo Syndrome

The Abducens Nerve

To the Editor: We read the article of Iaconetta et al.(1) describing the microscopic and endoscopic anatomy of the abducens nerve. The authors performed excellent work. They divided the abducens nerve into five segments, of which three are intracranial (cisternal, gulfar, cavernous) and two are orbital (fissural, intraconal). They stressed that the nerve courses in the cavernous sinus medially to the ophthalmic nerve and superiorly parallel to the petrolingual ligament (PLL). They added that the PLL is closely related to the medial surface of the dura and it covers both Meckel's cave and the ophthalmic branch of the trigeminal nerve with its sympathetic fibers. The PLL was meticulously inspected by us in a former study (2). The PLL is bow shaped and extends between the lingula of the sphenoid bone and the petrous apex. It has three parts: anterior tail, body, and posterior tail. The ligament is the posterior border of the cavernous sinus and lies under the junction of the maxillary and mandibular branches of the trigeminal nerve and the proximal part of the trigeminal root. The abducens nerve leaves the cavernous sinus at Dorello's canal through a triangle that was first described by our group (2,3). This triangle is constituted by the PLL, the petrosphenoidal ligament (Gruber's ligament), and the cavernous carotid artery. This means that the abducens nerve should not be superior to the PLL but inferior to it. On the other hand, the ophthalmic branch is anterior to the PLL. The abducens nerve may be stretched in this triangle as a result of various pathologies or increased intracranial pressure. Ibrahim M. Ziyal Tunçalp Özgen Ankara, Turkey

MICROANATOMICAL ARCHITECTURE OF DORELLO's CANAL AND ITS CLINICAL IMPLICATIONS

We investigated the membranous architecture of the abducens nerve at the petroclival region and describe the characteristics of this area in cadaveric specimen and two children with hydrocephalus and sixth nerve palsy using magnetic resonance imaging (MRI). Five adult cadaver heads were used to investigate the petroclival part of the abducens nerve. The heads were injected with colored latex for microsurgical dissection, and the length of the dural sleeve of the abducens nerve and its width at the apex were measured. In one cadaver head, the area between the petroclival entrance porus of the abducens nerve and the cavernous sinus was histologically studied under light microscopy. In two patients with hydrocephalus and abducens nerve palsy, the petroclival area was screened by using the MRI fat suppression technique. In the cadavers, the arachnoid membrane on the clivus extended within the dural sleeve as far as the petrous apex, as an extension of the subarachnoid space. The average length of the dural sleeve was 9.5 mm and the average width was 1.5 mm at the apex, where the nerve entered the cavernous sinus. MRI scans showed that the cerebrospinal fluid distance of the petroclival region was 5 mm in the first patient and 7 mm in the second. The subarachnoid space inside the dural sleeve of the abducens nerve can be defined by using thin-slice MRI scans. Enlargement of the dural sleeve at the petroclival region may coexist with the abducens nerve palsy. It has been documented in this study that the arachnoid membrane forms a membraneous barrier between the subarachnoid and subdural spaces within Dorello's canal.

Quantitative analysis of the working area and angle of attack for the retrosigmoid, combined petrosal, and transcochlear approaches to the petroclival region

The authors quantitatively assessed the working areas and angles of attack associated with retrosigmoid (RS), combined petrosal (CP), and transcochlear (TC) craniotomies. Four silicone-injected cadaveric heads were bilaterally dissected using three approaches progressing from the least to the most extensive. Working areas were determined using the Optotrak 3020 system on the upper and middle thirds of the petroclivus and brainstem. Angles of attack were studied using the Elekta SurgiScope at the Dorello canal and the origin of the anterior inferior cerebellar artery (AICA). The TC approach provided significantly greater (p < 0.001) working areas at the petroclivus (755.6 +/- 130.1 mm2) and brainstem (399.3 +/- 68.2 mm2) than the CP (354.1 +/- 60.3 and 289.7 +/- 69.9 mm2) and RS approaches (292.4 +/- 59.9, 177.2 +/- 54.2 mm2, respectively). The brainstem working area associated with the CP approach was significantly larger (p < 0.001) than that associated with the RS route. There was no difference in the petroclival working area comparing the CP and RS approaches (p = 0.149). The horizontal and vertical angles of attack achieved using the TC approach were wider than those of the CP and RS at the Dorello canal and the origin of the AICA (p < 0.001). The CP approach offers a more extensive working area than the RS for lesions involving the anterolateral surface of the brainstem, but not for petroclival lesions. The TC approach provides the widest corridor, improving the working area and angle of attack to both areas, but hearing must be sacrificed and the facial nerve is at risk.

Mikroanatomie des Sinus cavernosus

The surgical anatomy of the human cavernous sinus has been described by several authors. A clearer understanding of the anatomy of the cavernous sinus has resulted in an increased interest in surgical approaches to this region. Regarding the anatomical concept of the cavernous sinus previous descriptions should be revised. In our study, 35 skull-base blocks including both cavernous sinuses were investigated. There is considerable reason that the lateral wall of the cavernous sinus is covered by a "medial temporal dura layer" attached to the leptomeningeal pockets of the cranial nerves III-V1+2. There is no significant constance of the internal carotid artery within the cavernous sinus. All cranial nerves adjacent to or traversing the cavernous sinus are embedded within a leptomeningeal sheath similar to a pocket. The abducent nerve traverses a venous space, which should be named "petroclival venous confluence" rather than Dorello's canal. The extremely variable cavernous space is covered by a one-layer cell line. There is no evidence of any venous-plexus structure. Fibrose bands (trabecle) are present in different numbers.

Abducens schwannoma inside the cavernous sinus proper: case report

Background Only 2 cases of abducens nerve schwannoma solely inside the cavernous sinus have been reported. In both cases, abducens nerve palsy remained after operation. We report the first case of abducens nerve schwannoma inside the cavernous sinus proper with postoperative recovery from abducens nerve palsy. Case description The patient was a 47-year-old female who developed left abducens and trigeminal nerve palsies. Neuroradiological examination revealed left intra-cavernous sinus tumor. Total removal of the tumor was performed. The location of the tumor was confirmed intraoperatively inside the cavernous sinus itself, with no relation to the trigeminal nerve. Further, the relation of the tumor to one particular nerve fiber within the abducens nerve bundle was confirmed inside the cavernous sinus. After surgery, the patient had transient abducens nerve palsy. It had totally disappeared by 6 months. Conclusion When the tumor origin is just within the spacious cavernous sinus rather than more posterior in the narrow dural tunnel of Dorello's canal, successful preservation of the nerve function is possible postoperatively through a thorough knowledge of the membranous anatomy and careful preoperative study of the radiographic findings.

The sphenopetroclival venous gulf: a microanatomical study.

The sphenopetroclival area is the border zone between the middle and posterior cranial fossa. Several authors have studied the microsurgical anatomy of this region and have furnished sometimes contradictory descriptions of this area, which still represents a great challenge for the neurosurgeon. On the basis of previous anatomical data reported in the literature, the authors undertook a new microanatomical analysis of the sphenopetroclival region and report their findings. Twenty human cadaveric heads were used to reproduce, in the laboratory, different skull base approaches to expose the petroclival area. Measurements were taken in 40 specimens. From this study has emerged the finding that the sphenopetroclival area is a venous space, which the authors have named the "sphenopetroclival venous gulf" (SPCVG). The SPCVG is filled anteriorly by blood from the cavernous sinus (lateral sellar compartment [LSC], medially by blood from the basilar plexus, and laterally by blood from the superior petrosal sinus; this venous gulf is drained by the inferior petrosal sinus. The SPCVG is comparable in shape to an irregular hedron figure. It contains the Dorello canal, the venous segment of the abducent nerve, and the superior sphenopetrosal (Gruber) ligament, the fibers of which are in anatomical continuity with those of the inferior sphenopetrosal (petrolingual) ligament, forming a "falciform ligament." The structures defining the posterior surface of the SPCVG may represent a helpful surgical corridor through which it is possible to approach the LSC via the posterior fossa. This conceptualization of the SPCVG is an attempt to define univocally the microanatomy of the sphenopetroclival region in its entirety.

Detailed magnetic resonance imaging anatomy of the cisternal segment of the abducent nerve: Dorello's canal and neurovascular relationships and landmarks.

The goal of this study was to identify reliably the cisternal segment of the abducent nerve by using the three-dimensional Fourier transform constructive interference in steady-state (3-D CISS) magnetic resonance (MR) imaging sequence to define landmarks that assist in the identification of the abducent nerve on MR imaging and to describe the nerve's relationship to the anterior inferior cerebellar artery (AICA). A total of 26 volunteers underwent 3-D CISS MR imaging, and 10 of these volunteers also underwent MR angiography in which a time-of-flight sequence was used to identify the facial colliculus, the abducent nerve and its apparent origin, Dorello's canal, and the AICA. The authors identified the abducent nerve with certainty in 96% of 3-D CISS sequences obtained in the axial and sagittal planes and in 94% obtained in the coronal plane. The nerve emerged from the pontomedullary sulcus in 94% of cases. The facial colliculus could always be identified, and Dorello's canal was identified in 94% of cases. In 76.6% of cases, the abducent nerve was seen to contact the AICA, which passed inferior to the nerve in 63.8% of cases and superior to it in 29.8%. The anatomical course of the abducent nerve and its relationship to the AICA and other blood vessels can be reliably identified using a 3-D CISS MR sequence with the facial colliculus and Dorello's canal serving as landmarks.

Imaging of the normal pontine cisternal segment of the abducens nerve, using three-dimensional constructive interference in the steady state MRI.

Our objective was to determine the visibility of the cisternal segment of the normal abducens nerve using a three-dimensional Fourier-Transform constructive interference in the steady state (3DFT-CISS) sequence. Its visibility was rated in 150 patients without clinical evidence of abducens nerve disturbance. Axial 1-mm 3DFT-CISS images were obtained (TR/TE 17/7 ms, flip angle 50 degrees, field of view 160 mm, matrix 256 x 256). The cisternal segment was seen in 79% of cases, bilaterally in 73% and unilaterally in 11% of cases; neither cisternal segment was seen in 16% of cases. Identification of Dorello's canal was often of help in detecting the point lateral to the dorsum sellae at which the nerve pierces the dura mater. Flow artifacts and vascular loops in the pontine cistern sometimes caused problems in interpretation. 3DFT-CISS MRI with 1-mm-thick sections can however be considered a reasonably reliable technique for showing the cisternal segment of the abducens nerve.

Full Functional Recovery after Surgical Repair of Transected Abducens Nerve

OBJECTIVE AND IMPORTANCE: Results of surgical repair of the injured abducens nerve are rarely reported in the literature. A full functional recovery of a completely resected abducens root may be exceptional. We describe a patient who obtained normal ocular alignment and binocular vision after surgical reconstruction of a transected abducens nerve. CLINICAL PRESENTATION: A 56-year-old woman with a petroclival meningioma was presented. She underwent total removal of the tumor through a combined supra/infratentorial transpetrosal approach. The abducens nerve was tightly attenuated by the tumor and thickened dura. During dissection, the nerve was completely transected just behind the entrance to Dorello's canal. INTERVENTION: The abducens nerve was the single root type and inevitably required surgical repair. To obtain a sufficient length of the distal stump for trimming, part of the petrosphenoidal ligament was cut and the superior border of the petrous bone was exposed. The proximal stump of the nerve was also trimmed to obtain healthy tissue, and reconstruction was performed with five 10-0 nylon sutures. Five months later, esodeviation began to improve. Nine months after the surgery, the patient did not complain of diplopia and an objective assessment reported normal ocular alignment and estimated binocular function as excellent according to Biglan's system. Overcorrection of abduction did not occur. CONCLUSION: The result in our patient confirms the possibility of full functional recovery after surgical repair of a totally transected abducens nerve.

Surgical anatomy and approaches to tumors of Dorello??s canal

With the contemporary emphasis on preservation of vital neural and vascular structures during the removal of benign skull base lesions, surgeons are increasingly being challenged to adopt new and reconfigured approaches to the complex problems posed by skull base pathology. This review examines the microsurgical anatomy and approaches to Dorello's canal, a region that is uncommonly invaded by lesions of the petrous apex and clivus. It is this relative infrequency of tumor involvement that mandates surgeons to be intimately familiar with this anatomy.

A new concept in Dorello's canal microanatomy: the petroclival venous confluence.

The so-called Dorello's canal was studied in 32 specimens (16 human cadaver heads) injected with colored latex and fixed in formalin (28 specimens) or studied with microscopic and ultrastructural methods (four specimens). To avoid the differences usually encountered in the description of this area, the authors preferred to consider a larger space that they have named the petroclival venous confluence (PVC). It was located between two dural layers: inner (or cerebral) and outer (or osteoperiosteal). The PVC was quadrangular on transverse section. The posterior petroclinoid fold and the axial plane below the dural foramen of the abducent nerve (sixth cranial nerve) limited the PVC at the top and bottom, respectively. Its anteroinferior limit was the posterosuperior aspect of the upper clivus and outer layer of the dura mater. Its anterior limit was the vertical plane containing the posterior petroclinoid fold, and its posterior limit was the inner layer of the dura. The PVC was limited laterally by the medial aspect of the petrous bone apex and medially by the virtual sagittal plane extending the medial limit of the inferior petrosal sinus upward. The PVC was a venous space bordered by endothelium and continuous with the cavernous sinus, the basal sinus of the clivus, and the inferior petrosal sinus. There were trabeculations between the two dural layers. The petrosphenoidal ligament of Gruber may be regarded as a larger trabeculation, and it divided the PVC into a superior and an inferior compartment. The abducent nerve generally ran through the inferior compartment, where it was fixed to the surrounding dura mater. This nerve was only separated from venous blood by a meningeal sheath of varying thinness lined with endothelium. The clinical implications of these findings are discussed.

Microsurgical Study of the Dorello's Canal

The microsurgical anatomy of Dorello's canal was examined in 20 cadaver specimens. The study included dissections of this anatomic structure, under operative microscope and using microsurgical instruments. The detailed microanatomy of the canal was defined, as well as its relation to the sixth nerve, the clivus, the petrous apex, and the adjacent neurovascular elements.

The blood supply of the intracavernous cranial nerves: an anatomic study.

Cranial nerve deficits are the most common complications of cavernous sinus surgery. Often the deficit occurs despite anatomic preservation of the nerve, and ischemic injury is thought to be the cause. A better understanding of the blood supply of these nerves may help to prevent such complications. The authors performed a cadaveric microsurgical study of the intracavernous cranial nerves and their blood supply in 20 cavernous sinuses. The oculomotor nerve received branches from the inferolateral trunk or its equivalent in all specimens (100%). The proximal trochlear nerve received branches from the inferolateral trunk in 80% of the specimens and from the tentorial artery of the meningohypophyseal trunk in 20%. The distal half was supplied by the branches from the inferolateral trunk only. In the region of Dorello's canal, the proximal third of the abducens nerve received branches from the dorsal clival artery of the meningohypophyseal trunk. The middle and distal thirds received branches from the inferolateral trunk. The ophthalmic and proximal maxillary segments of the trigeminal nerve received branches from the inferolateral trunk. The distal maxillary segment was supplied by the artery of the foramen rotundum. In the majority of cases, the medial third of the Gasserian ganglion received branches from both the inferolateral trunk and the tentorial artery. The middle third of the ganglion received branches from either the inferolateral trunk or the middle meningeal artery. Our findings indicate the important role the intracavernous branches of the internal carotid artery play in the blood supply of the intracavernous cranial nerves, and stress the need to preserve these branches to prevent or minimize postoperative deficits.