Microsurgical Anatomy And Clinical Application Of Trigeminal Nerve

PARTⅠMicrosurgical Anatomy of Trigeminal NerveObjective: To explore the intracranial course of trigeminal nerve, and study thecharacter of the anatomical structure of trigeminal nerve, and gain the orientationregarding with Meckel's cave.Meterials and methods: Fifteen cadaver heads for a total of 30 sides were examined,using×2 to×40 magnification after perfusing the arteries and veins with colored latex.The skull was opened and the brain was carefully removed to expose the entire skullbase. The intracranial course of trigeminal nerve was exposed. The nerve wasmeasured under micrcoscope.Results: The length of the cisternal segment of the trigeminal nerve was17.64±1.93mm.The length, width and thickness of trigeminal ganglion were15.48±0.88mm, 12.41±1.31mm and 2.77±0.69mm. The length of V1 in Meckel'scave was 23.40±2.20mm, V2 was 12.06±1.38mm, V3 was 5.67±0.70mm.Thecisternal segment of the trigeminal nerve located in the prepontine cistern. Thetrigeminal nerve passes from the posterior fossa over the trigeminal impression of thepetrous apex between the periosteal and meningeal layers of middle fossa dura,carrying with it arachnoid and dura propria from the posterior fossa. The subarachnoidspace within Meckel's cave is behind the GG and is the actual space that constitutesthe trigeminal cistern. The gasserian ganglion was semilunar-shaped. Some rootlets inMeckel's cave cross each other; however, some are connected to each other and somecontinue without interruption, without crossing a rootlet and without making aconnection with a rootlet. This semilunar network has a plexiform appearance. Motorrootlets arose rostral to the sensory root, and followed or joined with V3 in theMeckel's cave. The most common finding at a vascular decompression operation for trigeminal neuralgia is a segment of the SCA compressing the trigeminal nerve. In our30 specimens, we found one SCA compressed the nerve, and 3 arteries and 1 branchcontacted with the nerve tightly. We also found 1 AICA contacted with the nervetightly. In 30 specimens, there was one trigeminal schwannoma was found.±Conclusions: The gasserian ganglion is a semilunar-shaped network which has aplexiform appearance. The trigeminal nerve enters, carrying with it arachnoid anddura propria from the posterior fossa. The subarachnoid space within Meckel's cave isis the actual space that constitutes the trigeminal cistern. Most cases of trigeminalneuralgia were thought to be the result of a pulsating blood vessel compressing thetrigeminal nerve at the root entry zone. The offending vessel was most commonly thesuperior cerebellar artery(SCA).Trigeminal schwannoma was the most commonlytumor arising from the nerve.PARTⅡMicrosurgical Anatomy of Meckel's CaveObjective: The anatomical shape, location and adjacent structures of the Meckel'scave were investigated, in order to gain the orientation regarding with temporal basetranstrntorial approach.Materials and methods: Fifteen cadaver heads for a total of 30 sides were examined,using×2 to×40 magnification after perfusing the arteries and veins with colored latex.The skull was opened and the brain was carefully removed to expose the entire skullbase. The Meckel's cave was exposed. The length, width and thickness of the cavewere measured under micrcoscope. The distances between the porus trigeminus andnear structures were also measured.Results: Meckel's cave was a dural recess extending from the posterior fossa to theposteromedial portion of the middle cranial fossa, the trigeminal ganglion and trigeminal cistern in it. Meckel's cave was constituted by superior wall, inferior wall,anterior wall, posterior wall, medial wall and lateral wall. The length, width andthickness of the Meckel's cave were 14.47±1.05mm, 15.10±1.30mm, 5.03±0.50mm.The porus trigeminus is an oval-shaped opening of Meckel's cave in posterior wallthat communicates with the posterior fossa. The medial wall of Meckel's cave wasthinness and close to cavernous sinus and Dorell's canal, and many significant nervesand vessels near it. The dural sleeve of the abducens nerve was located below the PSL,and the PLL invariably surrounded part of the dorsal and lateral walls of the lacerumsegment of the internal carotid artery (ICA), just under the anteroinferior portion ofthe anteromedial wall of Meckel's cave in all specimens. The distance between theporus trigeminus and the entrance site of trochlear nerve in the middle incisural space,the entrance site of abducent nerve in Dorello's canal, the entrance site of facial nervein internal auditory canal and the trigeminal nerve root entry zone were5.12±1.01mm, 9.32±0.98mm, 15.24±1.43mm and 11.21±1.86mm. There were thesuperior petrosal sinus and inferior petrosal sinus in posterior of Meckel's cave. Thegreater petrosal nerve(GSPN) crossed anterolaterally to the Meckel's cave, and it waslandmark to identify the lacerum segment of the ICA. The foramen rotundum, theforamen ovale and the foramen spinosum arranged laterally to the Meckel's cave inthe middle cranial fossa. The arcuate eminence located behind the foramenspinosum, which is the important landmark in the middle cranial fossa.Conclusion: The Meckel's cave cound communicate with the posterior craninal fossa,posterior part of fossa orbitalis, fossa pterygopalatina and fossa infratemporalis by theporus trigeminus, the superior orbital fissure, The foramen rotundum and the foramenovale. The medial wall of Meckel's cave was thinness, and which adjacent to thecavernous sinus and is the weak points of the meningeal wall for tumor invasion to orfrom the cavernous sinus. The petrosphenoidal ligament (PSL) and the petrolingualligament (PLL) are valuable anatomical landmarks for identifying the ICA andabducent nerve in this region. PARTⅢThe Study of The Clinical Features and Surgical Therapy of TrigeminalNeurinomasObjective: Trigeminal neurinomas are the second most common intracranialneurinomas next to the vestibular neurinomas.Methods: 84 patients with trigeminal neurinomas were treated between 2003 and2007, including 5 recurrent patients and 2 patients who failed toγradiotheraphy.Results: There were 40 women and 44 men (mean age 43 years). There were 24 typeA, 9 type B, 45 type C, and 6 type D tumors. Patients with neurofibromatosis Type 2were excluded. Among the 84 patients, five were recurrent, two were failure toGamma knife radiotherapy. These cases accounted for 0.6% of intracranial tumors and9.2% of intracranial neurinomas operated in our department during the same period.The most common early symptoms were headache (36/84) and numbness of theipsilateral hemiface (30/84). Erosion of the petrous apex and neighboring bonestructures was noted on CT scan in 16 of 43 patients. On T1-weighted sequences, thetumor appeared isointense or slightly hypointense. On T2-weighted sequences, thesetumors were either high signal or mixed with high and low signal. After contrastmedium, the solid part showed either homogeneous enhancement, and the capsulewall showed rim enhancement. Dextroscope virtual reality technology was used forpreoperative planning in recent 8 cases. In this series, the frontotemporal approachwas performed in 13 cases, the frontotemporal zygomatic approach in 30 cases, thefrontotemporal orbitozygomic approach in 18 cases, the subtemporal approach in 7cases, the retrosigmoid approach in 14 cases, the transmandibular approach in 1 case,and the combined frontotemporal-retrosigmoid method in 1 case. Gross total resectionwas achieved in 63 (75%) patients, near-total resection was achieved in 3 (3.6%)patients, and subtotal cytoreductive resection was achieved in 18 (21.4%) patients.The impediments to complete removal were adherent to the brainstem (9/21),adherent to important vascular structure (6/21), inadequate exposure(4/21), cavernous sinus involvement(2/21). Postoperative complications included meningitis in 6patients, hydrocephalus in 3 patients, epidural hematoma in 2 patients, cerebrospinalfluid (CSF) leak in 1 patient. The follow-up period ranged from 10 to 60 months(average 25 months) in 65 patients. No tumor recurrence was observed in follow-uppatients.Conclusion: The typical CT and MRI findings are contribute to the diagnoses of thetrigeminal neurinomas. The frontotemporal approach with zygomatic ororbitozygomic osteotomy or subtemporal approach could offer excellent exposure ofthe middle fossa and access to the posterior fossa. The trigeminal neurinomas couldbe removed by the frontotemporal approach with or without zygomatic ororbitozygomic osteotomy, the subtemporal approach, the retrosigmoid approach, et al.Dextroscope virtual reality technology was a very useful tool to identify surgical andanatomic nuances and enhance preoperative planning in trigeminal neurinomasresection.PARTⅣTemporal Base Transtentorial Approach to The Dumbbell-Shaped TrigeminalSchwannomaObjective: To investigate temporal base transtentorial approach for thedumbbell-shaped trigeminal schwannoma, study the clinical significance of theMeckel's cave.Methods: The clinical data of 6 dumbbell-shaped trigeminal schwannoma, operatedwith the temporal base transtentorial approach from 2003 to 2007, were reviewed.Results: There were no severe postoperative complications in the 6 patients. Thenumbness of the ipsilateral hemiface in 1 patient could not recovery. The abducensnerve palsy in 1 patient was short-lived. No additional cranial nerves paralysis werenoticed postoperatively. There was no surgical mortality. The follow-up period ranged from 18 to 60 months (average 37 months) in 6 patients. No tumor recurrence wasobserved in follow-up patients.Conclusion: The temporal base transtentorial approach has become our standardapproach to the dumbbell-shaped trigeminal schwannoma. Advantages of the surgicalapproaches are wide operating field to the middle fossa, CS, Meckel cave, andtrigeminal pore; unnecessary to drill the petrous apex for resection of tumors in theCPA; safely removing the tumor in the posterior cranial fossa and the CPA underdirect visualization; no need special reconstruction because of limited bone removalof the middle cranial base. Open the trigeminal pore or tentorial incisura after theentrance site of trochlear nerve in the middle incisural space, the structures in CPAcould be showed clearly.