Porus Trigeminus Research Articles

128 The Sagittal Angle of the Trigeminal Nerve at the Porus Trigeminus is a Radiologic Predictor of Surgical Outcome in Microvascular Decompression for Classical Trigeminal Neuralgia

INTRODUCTION: Classical Trigeminal Neuralgia (cTN) is a facial pain syndrome with specific diagnostic criteria, including paroxysms that last 1-120 seconds, are sharp, stabbing, or electric in character, and are induced by innocuous stimuli. The most commonly accepted cause of cTN is neurovascular compression (NVC) of the proximal cisternal segment of the trigeminal nerve by an adjacent artery. Microvascular decompression surgery (MVD) provides immediate and durable relief in many patients. METHODS: Pre-operative MRIs from 300 patients with cTN who underwent MVD were analyzed to identify patients with a hyperacute SATNaPT (defined as less than 3 standard deviations below the mean). The rate of surgical success (pain-free after at least 12 months) was compared between patients with a hyperacute SATNaPT and all other patients. RESULTS: Patients without a hyperacute SATNaPT had an 82% likelihood of surgical success, whereas patients with a hyperacute SATNaPT had a 58% likelihood of surgical success (p < 0.05). Patients with a hyperacute SATNaPT who also had no evidence of vascular compression on preoperative MRI had an even lower likelihood of success (29%, p < 0.05). CONCLUSIONS: In patients with cTN being considered for MVD, a hyperacute SATNaPT is a negative prognostic biomarker that predicts a higher likelihood of surgical failure. Patients with a hyperacute SATNaPT, particularly those without MRI evidence of vascular compression, may benefit from other surgical treatments or a modification of MVD to adequately address the underlying cause of cTN.

Surgical Anatomy of the Retrosigmoid Approach With Transtentorial Extension: Protecting the 4th Cranial Nerve.

The retrosigmoid approach with transtentorial extension (RTA) allows us to address posterior cranial fossa pathologies that extend through the tentorium into the supratentorial space. Incision of the tentorium cerebelli is challenging, especially for the risk of injury of the cranial nerve (CN) IV. We describe a tentorial incision technique and relevant anatomic landmarks. The RTA was performed stepwise on 5 formalin-fixed (10 sides), latex-injected cadaver heads. The porus trigeminus's midpoint, the lateral border of the suprameatal tubercle (SMT)'s base, and cerebellopontine fissure were assessed as anatomic landmarks for the CN IV tentorial entry point, and relative measurements were collected. A clinical case was presented. The tentorial opening was described in 4 different incisions. The first is curved and starts in the posterior aspect of the tentorium. It has 2 limbs: a medial one directed toward the tentorium's free edge and a lateral one that extends toward the superior petrosal sinus (SPS). The second incision turns inferiorly, medially, and parallel to the SPS down to the SMT. At that level, the second incision turns perpendicular toward the tentorium's free edge and ends 1 cm from it. The third incision proceeds posteriorly, parallel to the free edge. At the cerebellopontine fissure, the incision can turn toward and cut the tentorium-free edge (fourth incision). On average, the CN IV tentorial entry point was 12.7 mm anterior to the SMT base's lateral border and 20.2 mm anterior to the cerebellopontine fissure. It was located approximately in the same coronal plane as the porus trigeminus's midpoint, on average 1.9 mm anterior. The SMT and the cerebellopontine fissure are consistently located posterior to the CN IV tentorial entry point. They can be used as surgical landmarks for RTA, reducing the risk of injury to the CN IV.

Surgical Strategy for Petroclival Meningioma-Related Trigeminal Neuralgia: The Role of Porus Trigeminus Opening

ObjectivePetroclival (PC) meningiomas invade Meckel's cave through the porus trigeminus, leading to secondary trigeminal neuralgia (TN). Microsurgery and stereotactic radiosurgery (SRS) are the typical treatment options. This study investigated symptom control, outcomes, and surgical strategies for PC meningioma-induced TN. MethodsWe retrospectively analyzed 28 TN patients with PC meningiomas who underwent microsurgical nerve decompression between January 2021 and February 2023. In all patients undergoing a transpetrosal approach, the porus trigeminus was opened to enable the removal of the entire tumor within Meckel’s cave. Clinical outcomes were assessed using the Barrow Neurological Institute (BNI) pain intensity scale. Risk factors for poor TN outcomes and poor facial numbness were analyzed. ResultsAmong 28 patients, 21 (75%) underwent the transpetrosal approach, 5 (17.9%) underwent the retrosigmoid approach, and 2 (7.1%) underwent the Dolenc approach. Following microsurgery, 23 patients (82.1%) experienced TN relief without further medication (BNI I or II). TN recurrence occurred in 2 patients (7.1%), and 3 patients (10.7%) did not achieve TN relief. Cavernous sinus invasion was significantly correlated with poor TN outcomes (p=0.047). A history of previous SRS (p=0.011) and upper clivus type tumor (p=0.018) were significantly associated with poor facial numbness. ConclusionsMicrosurgical nerve decompression is effective in improving BNI scores in patients with TN associated with PC meningiomas. Considering the results of our study, the opening of the porus trigeminus can be considered as a suggested procedure in the treatment of PC meningiomas, especially in cases accompanied by TN.

An anatomical study of the subarachnoid space surrounding the trigeminal ganglion in horses-in preparation for a controlled glycerol rhizotomy in equids.

Equine trigeminal-mediated headshaking is a painful neuropathic disorder comparable to trigeminal neuralgia in humans. The selective destruction of pain fibers within the trigeminal ganglion, called rhizotomy, is the surgical treatment of choice for idiopathic trigeminal neuralgia refractory to medical treatment in humans. The human trigeminal ganglion is enclosed by a dural recess called the Meckel's or trigeminal cave, in which the ganglion is surrounded by a cerebrospinal fluid (CSF)-filled subarachnoid space. During glycerol rhizotomy, glycerol is percutaneously injected in this CSF-filled space. Until now, information about the anatomy of the dural recess and the subarachnoid space surrounding the trigeminal ganglion is lacking in horses. The aim of this study was to explore if a CSF-filled subarachnoid space around the trigeminal ganglion exists in horses. Six equine cadaver heads were investigated for CSF accumulation around the ganglion with a 3 Tesla MRI. After anatomical dissection to expose the trigeminal root, a polymer-based radiopaque contrast agent was injected through the porus trigeminus into the subarachnoid space (cisternography). The exact delineation and the volume of the contrast agent accumulation were determined on subsequent micro-computed tomographic scans and segmentation. Finally, the distribution of the contrast agent within the subarachnoid space was examined histologically in three specimens. In all 12 specimens included in this study, the trigeminal ganglion was surrounded by a subarachnoid space forming a trigeminal cistern. The mean volume of the trigeminal cave in this study was 0.31 mL (±SD: 0.11 mL). Distribution of the contrast agent along the peripheral nerves (i.e., ophthalmic, maxillary and/or mandibular nerve) was observed in 7 out of 12 specimens. A subarachnoid space surrounding the trigeminal ganglion exists in the horse and could be targeted for glycerol rhizotomy in horses suffering from trigeminal-mediated headshaking. However, the clinical relevance of contrast agent distribution along the peripheral nerves remains to be assessed.

Internal Neurolysis for Trigeminal Neuralgia: A Preliminary Single-institution Experience in Japan.

Internal neurolysis (IN) is a surgical procedure in which the trigeminal fibers are separated between the pons and porus trigeminus to relieve trigeminal neuralgia (TN). Recent investigations revealed that the number of nerve bundles made by IN varies, and immediate postoperative hypesthesia exceeded 90% and pain control rate at 1 year was 77%-93.5%. We present the preliminary experience of 18 patients who underwent IN for TN between June 2020 and June 2022. The Barrow Neurological Institute pain scale (BNI-PS) was recorded preoperatively and in June 2023, and the Barrow Neurological Institute hypesthesia scale (BNI-HS) was recorded preoperatively, immediate postoperatively and in June 2023. Intraoperatively, the number of bundles made by IN was reviewed. Preoperative BNI-PS ranged between VI and V. Two patients experienced BNI-HS II due to percutaneous procedure prior to IN. Intraoperatively, 3 bundles were made by IN in 7 patients, 4 bundles in 5, and 5 bundles in 6. Immediate postoperative BNI-HS I was recorded in 6 patients and II in 12 (66.7%). The last follow-up revealed that BNI-PS I and II were recorded in 13 patients (72.2%) and BNI-HS I and II in 6 patients, respectively. Our results demonstrated that the rates of immediate postoperative hypesthesia (66.7%) and pain control (72.2%) at 1 year or later were below those of previous reports. Therefore, we are currently combing to make at least 6 bundles. Detailed surgical technique and cardiac reflex alerts during the procedure are described.

The Sagittal Angle of the Trigeminal Nerve at the Porus Trigeminus is a Radiologic Predictor of Surgical Outcome in Microvascular Decompression for Classical Trigeminal Neuralgia.

Classical trigeminal neuralgia (cTN) is a painful disease. Microvascular decompression (MVD) provides immediate and durable relief in many patients. A variety of positive and negative prognostic biomarkers for MVD have been identified. The sagittal angle of the trigeminal nerve at the porus trigeminus (SATNaPT) is an MRI biomarker that can identify a subset of patients with cTN whose trigeminal nerve anatomy is different from normal controls. The purpose of this case-control study was to determine whether an abnormally hyperacute SATNaPT is a negative prognostic biomarker in patients with cTN undergoing MVD. Preoperative MRIs from 300 patients with cTN who underwent MVD were analyzed to identify patients with a hyperacute SATNaPT (defined as less than 3 SDs below the mean). The rate of surgical success (pain-free after at least 12 months) was compared between patients with a hyperacute SATNaPT and all other patients. Patients without a hyperacute SATNaPT had an 82% likelihood of surgical success, whereas patients with a hyperacute SATNaPT had a 58% likelihood of surgical success ( P < .05). Patients with a hyperacute SATNaPT who also had no evidence of vascular compression on preoperative MRI had an even lower likelihood of success (29%, P < .05). In patients with cTN being considered for MVD, a hyperacute SATNaPT is a negative prognostic biomarker that predicts a higher likelihood of surgical failure. Patients with a hyperacute SATNaPT, particularly those without MRI evidence of vascular compression, may benefit from other surgical treatments or a modification of MVD to adequately address the underlying cause of cTN.

Comparative Analysis of Surgical Working Corridors for Meckel Cave Trigeminal Schwannomas: A Quantitative Anatomic Study.

Volumetric analysis of the working corridors of the interdural approach to the Meckel cave may lead to a selection of routes which are anatomically more advantageous for trigeminal schwannoma resection. The herein-reported anatomic study quantitively compares the infratrochlear (IT) transcavernous, anteromedial (AM), and anterolateral (AL) corridors, highlighting their feasibility, indications, advantages, and limitations. Anatomic boundaries and depth of Meckel cave, porus trigeminus, IT transcavernous, AM, and AL corridors were identified in 20 formalin-fixed latex-injected cadaveric heads and were subsequently measured. The corridor areas and volumes were derived accordingly. Each opening angle was also calculated. Angles and volumes were compared using analysis of variance. Statistical significance was set at a P -value <.05. The IT transcavernous corridor volume was greater than that of the AM and AL. The opening angle of the AM middle fossa triangle was wider than the other 2. The IT corridor can be advantageous for Meckel cave schwannomas invading the cavernous sinus and those with a notable extension into the posterior fossa because the transcavernous approach maximizes the working space into the retrosellar area. The AM middle fossa corridor is strategic in schwannomas confined to the Meckel cave with a minor extension into the posterior fossa. It raises the chance of total resection with a single approach involving the porus trigeminus opening.

Sagittal Angle of the Trigeminal Nerve at the Porus Trigeminus: A Novel Measurement to Distinguish Different Causes of Classic Trigeminal Neuralgia.

Classic trigeminal neuralgia is a clinical syndrome of facial pain, most often attributable to vascular compression of the proximal cisternal segment of the trigeminal nerve and treatable with microvascular decompression of the nerve. Some patients, however, meet all clinical criteria for classic trigeminal neuralgia yet do not respond to microvascular decompression. Because the reasons for surgical failure are not well understood, the aim of this study was to determine if a subset of patients with classic trigeminal neuralgia could be distinguished by measuring the angle of the trigeminal nerve in the sagittal plane as the nerve traverses the porus trigeminus. We retrospectively identified patients with either classic trigeminal neuralgia (n = 300) or hemifacial spasm (n = 300) who had undergone MR imaging, including 3-plane steady-state free precession imaging. Patients with hemifacial spasm served as controls. On sagittal steady-state free precession images, we measured the angle of each trigeminal nerve as it crosses through the porus trigeminus into the Meckel cave (SATNaPT). In patients with classic trigeminal neuralgia, we separated the nerves into symptomatic and asymptomatic sides. We compared these 3 groups using the Student t test. Control patients had a mean SATNaPT of 170° (SD, 11°) with a normal distribution. The contralateral asymptomatic nerve in patients with classic trigeminal neuralgia had the same distribution of angles. The symptomatic nerves in patients with classic trigeminal neuralgia had a bimodal distribution; 83% of patients fell into the same distribution as the asymptomatic nerves, but the other 15% had an average angle of 143° (SD, 7°). This difference was statistically significant (P < .0001). Patients with the clinical syndrome of classic trigeminal neuralgia fell into 2 categories based on the radiologic measurement of the SATNaPT. Most patients had an anatomically normal nerve that was affected by vascular compression, but 17% of these patients had aberrant anatomy that may cause or contribute to their clinical presentation. Further study is needed to determine whether this subset of patients should receive a different surgery to better address their underlying anatomic abnormality. The SATNaPT measurement should be included in every MR imaging interpretation performed on patients with classic trigeminal neuralgia.

Impact of C-shaped skin incision on surgical operability in the retrosigmoid approach: when a good start is half of the job.

The retrosigmoid approach (RSA) is one of the routes of choice to approach tumors and vascular lesions of the cerebellopontine angle. Among different types of skin incisions and soft tissue dissection techniques, the most widely used variants comprise the straight/lazy S-shaped and the C-shaped incisions. Several reports discuss advantages in terms of functional and clinical outcomes of the C-shaped incision, but scientific considerations about the critical impact of this kind of incision on surgical operability are still extremely limited. Authors comparatively analyze the advantage provided by C-shaped incision in RSA in terms of anatomic exposure and surgical operability, compared with straight/lazy S-shaped one. A comparative microanatomical laboratory investigation was conducted. The operability score (OS) was applied for quantitative analysis of surgical operability. C-shaped incision, providing a significant reduction of the overall working distance (-13%) together with an overall increase of the maneuverability area (+ 204.9%), did improve the conizing effect on the surgical corridor. It optimized overall maneuverability of surgical instruments, in terms of angle of attack (+ 27.7%), as well as maneuverability arc (+ 122%), on the entire surgical field. C-shaped incision ensured good operability on all surgical targets (OS ranging from 2 to 3), most significantly improving surgical maneuverability at the porus trigeminus and internal acoustic meatus. C-shaped incision in the RSA significantly improves anatomic exposure and surgical operability as compared with straight/lazy S-shaped incision.

Commentary: Anterior Petrosal Approach for Enlarging Previously Radiated Recurrent Trigeminal Schwannoma: 2-Dimensional Operative Video.

Trigeminal nerve schwannomas (TNSs) are rare lesions that typically present with symptoms of trigeminal neuropathy or other cranial nerve palsies. These lesions classically have a dumbbell shape, with an anterior component within Meckel's cave and posterior component extending into the posterior fossa through the porus trigeminus. Surgical resection of TNSs can often be achieved via an extradural subtemporal approach to Meckel's cave without an anterior petrousectomy, even for tumors with a significant posterior fossa component, as the tumor often erodes a portion of the petrous apex.1 We present the case of a 53-yr-old female presenting to our institution with complete trigeminal neuropathy secondary to a right-sided, previously resected and radiated TNS. Serial imaging demonstrated an interval growth of significant residual tumor despite multiple adjuvant therapies, and, thus, the patient was recommended to undergo additional surgical resection. The lesion was approached through a right-sided subtemporal approach to Meckel's cave,2 with a plan to utilize an anterior petrousectomy only if difficulty resecting the posterior fossa component of the tumor was encountered. Intraoperatively, the posterior fossa component was found to be densely adherent to the adjacent brainstem, likely secondary to prior surgery and radiation therapy, and, thus, an anterior petrousectomy was performed. Postoperatively, the patient had stable trigeminal neuropathy without any new neurological deficits and a magnetic resonance imaging (MRI) confirmed a gross total resection. In the accompanying video, we hope to demonstrate the steps and nuances of both the subtemporal approach to accessing Meckel's cave and anterior petrousectomy when employed for the resection of TNSs. The patient in question provided formal consent for the making of this video.

Anterior Petrosal Approach for Enlarging Previously Radiated Recurrent Trigeminal Schwannoma: 2-Dimensional Operative Video

Trigeminal nerve schwannomas (TNSs) are rare lesions that typically present with symptoms of trigeminal neuropathy or other cranial nerve palsies. These lesions classically have a dumbbell shape, with an anterior component within Meckel's cave and posterior component extending into the posterior fossa through the porus trigeminus. Surgical resection of TNSs can often be achieved via an extradural subtemporal approach to Meckel's cave without an anterior petrousectomy, even for tumors with a significant posterior fossa component, as the tumor often erodes a portion of the petrous apex.1 We present the case of a 53-yr-old female presenting to our institution with complete trigeminal neuropathy secondary to a right-sided, previously resected and radiated TNS. Serial imaging demonstrated an interval growth of significant residual tumor despite multiple adjuvant therapies, and, thus, the patient was recommended to undergo additional surgical resection. The lesion was approached through a right-sided subtemporal approach to Meckel's cave,2 with a plan to utilize an anterior petrousectomy only if difficulty resecting the posterior fossa component of the tumor was encountered. Intraoperatively, the posterior fossa component was found to be densely adherent to the adjacent brainstem, likely secondary to prior surgery and radiation therapy, and, thus, an anterior petrousectomy was performed. Postoperatively, the patient had stable trigeminal neuropathy without any new neurological deficits and a magnetic resonance imaging (MRI) confirmed a gross total resection. In the accompanying video, we hope to demonstrate the steps and nuances of both the subtemporal approach to accessing Meckel's cave and anterior petrousectomy when employed for the resection of TNSs. The patient in question provided formal consent for the making of this video.

Internal neurolysis: ‘nerve combing’ for trigeminal neuralgia without neurovascular conflict – early UK outcomes

Introduction Internal neurolysis (INL) is a surgical procedure where trigeminal nerve fibres are separated between the pons and porus trigeminus to relieve trigeminal neuralgia (TN). We report pain and functional outcomes to evaluate its safety and efficacy. Materials and methods Prospective cohort of all patients undergoing retrosigmoid craniotomy and INL between 2015 and 2017 at University Hospital Southampton. Patients with type I (6) or type II (2) refractory TN and no clear neurovascular conflict were offered INL as an alternative to partial sensory rhizotomy. Barrow Pain Intensity Scale (BNI) and Brief Pain Inventory Facial scores (BPI-Facial) were assessed. Minimum follow-up was 2 years'. Results Eight patients (7F:1M) underwent INL. Two had MS. Pre-operatively, all had severe pain (BNI grade V) and the median BPI-Facial score was 115 (range 79–123).. There were no unexpected complications. On last follow-up, six (75%) had no pain (BNI grade I), while two (25%) had recurred (at 5 and 27 months). Median BPI-Facial score for all patients on the last follow-up was 20 (range 18–91) reflecting dramatically improved quality of life and activities. Conclusions INL is a potentially safe and effective treatment for refractory TN. Long-term efficacy is unknown, but early results are promising.

The Size and Shape of the Porus Trigeminus: Implications for Trigeminal Neuralgia Procedures

Trigeminal neuralgia is characterized by debilitating facial pain. The treatment for trigeminal neuralgia often involves the introduction of a surgical tool through the foramen ovale and porus trigeminus (PT). Though several studies have recently described the anatomy of the foramen ovale, few have described the PT. This study analyzed 53 PT for area, height, width, and circularity among both left‐ and right‐sided PT from females and males. There were no statistically significant differences in the area, height, width, and circularity of the PT between sexes (U=258, p=0.42; U=255, p=0.38; U=298, p=0.99; U=295.5, p=0.95). Similarly, paired t‐tests revealed no significant differences between sides with regard to area (t=1.35; p=0.19) and height (t=0.40; p=0.69). However, there were significant differences between sides with regard to width (t=2.19; p=0.04) and circularity (t=3.38; p=0.003). The average left‐sided PT width was 6.6±2.4mm (Mean±SD) whereas the average right‐sided PT width was 7.7±1.6mm. With regard to surgical implications, right‐sided PT may provide slightly greater freedom with regard to the angle of approach to the PT.Support or Funding InformationFunding: WV Research Challenge Fund [HEPC.dsr.17.06]This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Posterior Approach to Meckel's Cave: Retrosigmoid Craniectomy with Endoscopic Assistance.

Background Meckel's cave involvement in tumors pose a challenge due to their surrounding neurovascular structure and deep location. Case Review A 24-year-old male presented with progressive headaches and right sided trigeminal neuralgia with a large epidermoid. The tumor extended from the ambient cistern to the cerebellomedullary cistern and involved Meckel's cave ( Fig. 1 ). Technical Note/Video Description A retrosigmoid craniectomy was performed. Cranial nerves 3, 4, 6, 7, and 10, and auditory brainstem responses were monitored. Once the craniectomy was completed the dura was opened and cerebrospinal fluid (CSF) was released from the cisterna magna to allow for the tumor resection to be done without the use of any retractors ( Fig. 2 ). Care was taken to ensure that cranial nerves in the posterior fossa were detethered to prevent any traction injury. Using ring curettes the pearly white epidermoid tumor was able to be debulked. After all the possible tumor was resected with the microscope, the 30-degree endoscope was used to identify the porus trigeminus. Malleable ring curettes and a malleable suction were used to remove the soft tumor from this location. The patient transiently had loss of hearing but this returned within 2 weeks after surgery. Conclusions The retrosigmoid approach is familiar to all neurosurgeons and with the adjunct of an angled endoscope, the posterior Meckel's cave can be easily reached. This is particularly useful for tumors with soft consistency. The assistance of the endoscope allows Meckel's cave visualization without additional drilling while still allowing safe resection of tumor from around the trigeminal nerve. The link to the video can be found at: https://youtu.be/01aqOyUmSW0 .

A Combined Extradural–Intradural Technique for an En Bloc Anterior Petrosectomy: A Cadaveric Feasibility Study

The anterior petrosectomy approach is among the most popular for exposure of the petroclival region. However, the complexity of the anatomy, drilling time required, and risk of injury to neurovascular structures have made this procedure especially challenging. We have proposed a novel combined extradural-intradural technique for en bloc anterior petrosectomy-or one-piece Kawase-and have charted the landmarks that define its surgical boundaries. The approach was performed on 14 embalmed specimens. The one-piece Kawase approach consists of 3 extradural drilling steps, followed by incision of the dura and skeletonization of the superior petrosal sinus. The procedure culminates with 2 intradural drilling steps. The bone piece was then removed en bloc, and the maximum anteroposterior, superoinferior, and mediolateral lengths were recorded. The linear distances between the main neurovascular landmarks were also measured using a stereotactic navigation system. The mean measurements were 17.6 ± 2.6 mm for the anteroposterior distance, 10.5 ± 2.3 mm for the superoinferior distance, and 9.5 ± 2.6 mm for the mediolateral distance. The medial linear distance from the mandibular nerve/greater superficial petrosal nerve to the internal carotid artery was 6.8 ± 1.3 mm, to the facial hiatus was 11.6 ± 2.2 mm, and to the lateral internal acoustic canal was 17.9 ± 1.8 mm. The average distance from the porus trigeminus to the medial internal acoustic canal was 19.4 mm. The advantages of this technique include the wide exposure of the petroclival region, extensive visualization of critical structures via extradural and intradural corridors, and minimization of bone drilling, which could reduce heat damage. Clinical application of the illustrated technique is required to test its reliability in different pathological subsets.

Ossification of the Posterior Petroclinoid Dural Fold: A Cadaveric Study with Neurosurgical Significance.

Objectives The roof of the porus trigeminus, composed of the posterior petroclinoid dural fold, is an important landmark to the skull base surgeon. Ossification of the posterior petroclinoid dural fold is an anatomical variation rarely mentioned in the literature. Such ossification results in the trigeminal nerve traversing a bony foramen as it enters Meckel cave. The authors performed this study to better elucidate this anatomical variation. Design Fifteen adult cadaveric head halves were subjected to dissection of the middle cranial fossa. Microdissection techniques were used to examine the posterior petroclinoid dural folds. Skull base osteology was also studied in 71 dry human skulls with attention paid to the attachment point of the posterior petroclinoid dural folds at the trigeminal protuberances. Setting Cadaver laboratory Main Outcome Measures Measurements were made using a microcaliper. Digital images were made of the dissections. Results Completely ossified posterior petroclinoid folds were present in 20% of the specimens. Of the 142 dry skull sides examined, 9% had large trigeminal protuberances. Conclusions Based on this study, the posterior petroclinoid dural fold may completely ossify in adults that may lead to narrowing of the porus trigeminus and potential compression of the trigeminal nerve at the entrance to Meckel cave.

Endoscopic Endonasal Approach to Meckel's Cave

Objectives: External approaches to Meckel’s Cave (MC) and petrous carotid artery offer excellent exposure but are associated with neurological-cosmetic-functional morbidities. Our aim is to describe an endoscopic approach to MC while providing anatomical relationships, predictable morbidities, and clinical applications. Methods: Four cadaveric heads (8 sides) were dissected with 0° endoscopy through transnasal-transmaxillary-transsphenoid-transpterygoid approach. Results: A large maxillary antrostomy was performed and the sphenopalatine artery identified; the posterior and superior walls of maxillary sinus were removed, the pterygopalatine fossa (PPF) exposed, and the internal maxillary artery and maxillary nerve (V2) entering foramen rotundum identified. Lateral to pterygoid buttress, medial attachments of lateral pterygoid muscle were dissected, and the mandibular nerve (V3) in the infratemporal fossa (ITF) entering foramen ovale was exposed. A large sphenoidotomy was performed and cavernous carotid artery located. The Vidian was followed retrogradely until identifying foramen lacerum and then petrous carotid artery. The ophthalmic nerve (V1) was identified in the superior orbital fissure and Gasserian ganglion (GG) in MC in the petrous apex. The GG was followed posteriorly to the retrogasserian root and porus trigeminus. Conclusions: The described endoscopic approach affords the same exposure as external approaches with less morbidity. Indications include lesions of MC, PPF, ITF with minimal intracranial extension and biopsy of suspected malignant tumors in these areas. Limitations of the technique are massive intracranial tumor extension and difficulties to control bleeding in a narrow space. Morbidity will be discussed based on anatomical dissection. Illustrative clinical cases with videos will be presented to support this approach.

Neural interconnections between portio minor and portio major at the porus trigeminus: Application to failed surgical treatment of trigeminal neuralgia

Recalcitrant trigeminal neuralgia following surgical treatment can be a life-altering condition. To explore alternative anatomic reasons for such a complication, the authors examined the potential for nerve connections between the sensory and motor roots of the trigeminal nerve at the opening of Meckel's cave (porus trigeminus). In 15 embalmed adult cadavers (30 sides), the authors performed microdissection of the skull base and specifically at the opening of Meckel's cave. Two sides (6.67%) were found to have interneural connections between the sensory and motor roots at Meckel's cave. These occurred in one male and one female cadaver, both on right sides. Both connections were histologically verified to be neural and were 0.5 mm in diameter and 2.2 and 3.2 mm in length, respectively. Both connections traveled in an oblique fashion from the portio major to the portio minor. On the basis of authors' findings, the sensory and motor components of the trigeminal nerve at the opening of Meckel's cave may be interconnected with a neural anastomosis. Such findings may be of use during the surgical treatment of trigeminal neuralgia or other surgery of the posterior fossa so that inadvertent transection or traction does not occur.

The relationship between the superior petrosal sinus and the porus trigeminus: an anatomical study

During intracranial approaches to the skull base, vascular relationships are important. One relationship that has received scant attention in the literature is that between the superior petrosal sinus (SPS) and the opening of the Meckel cave (that is, the porus trigeminus). Cadaver dissections were performed in 25 latex-injected adult cadaveric heads (50 sides). Specifically, the relationship between the SPS and the opening of the Meckel cave was observed. The goal was to enhance knowledge of the relationship between the SPS and the opening of the Meckel cave. Of the 50 sides, 68%, 18%, and 16% of SPSs traveled superior to, inferior to, and around the opening to the Meckel cave, respectively. In the latter cases, a venous ring was formed around the proximal trigeminal nerve. No sinus entered the Meckel cave. In general, the porus trigeminus was narrowed on sides found to have an SPS that encircled this region. Sinuses that traveled only inferior to the porus were in general smaller than sinuses that traveled superior or encircled this opening. No statistically significant differences were noted between the various sinus relationships and sex, age, or side of the head. Knowledge of the relationship between the SPS and the opening of the Meckel cave may be useful to the skull base surgeon. Based on this study, some individuals may retain the early embryonic position of their SPS in relation to the trigeminal nerve.

Neural Interconnections Between Portio Minor and Portio Major at the Porus Trigeminus

Neural Interconnections Between Portio Minor and Portio Major at the Porus Trigeminus