Microsurgical Anatomy Of The Hypoglossal Canal Area And Its Surgical Approach

Purpose: To study the the morphology and dimension and relation of the osseous hypoglossal canal (HC) and its adjacent bony structures for further study of surgical approach in this area .Methods: Bony HC and its adjacent bony structures were observed and measured on 20 dry skulls and 15 dry atlases , CT scans of 15 wet cadaveric head- neck specimens of adults were obtained . The distances between HC and its adjacent bony structures were measured, and the distances between different important structures and different locations of HC were al so measured and the data differences between bilateral sides were statistically analysed.Results: The HC was located at the anterolateral margin of magnum foramen and between the jugular tubercle and the occipital condyle and anterior, medial and inferior to the jugular foramen. Its length ,width and thickness in left and right side was 11.2+1. 3mm, 11. 3± 1. 3mm,3.5 +1. 6mnu4. 3+1. 2mm, 5.2+1. 6mnu5. 4+1. 3mm, respectively, and the angle formed by HC and sagittal plane in left and right side was 41.1 +4. 6, 40. 5 + 6. 0 degrees , respectively; and the one formed by HC and condylar canal which was present 60% was 47 + 2. 7 degrees and 47.7 + 2. 7 degrees in left and right sides,respectively ;the the intracranial orifice of HC and the anterior orifice of condylar canal was not connected but seperated by a thin bony slice , which was thick 2~3mm. The distance from the upper surface of jugular tubercle to the upper wall of HC in left and right side was 5.3+1.8mm and 4.8+1.6mm respectively; The distance from the posterior rim of the occipital condyle to the intracranial orifice,the midpoint and the extracranial orifice of HC was 14.2 + 2.5mm 13.6 + 2.4mm, 14.5 + 1.5mm 15.8 + 1.8mm, 18.2+1.7mm 19.1 +2.8mm,respectively. The length of the transverse process of the atlas(TPA) in left and right side was 15 + 1.9mm and 15.6+ 1.4mm , respectively, and the distance between TPA and occipital bone was 7.6 + 4. lmm and 5. 8 + 2. 5mm, respectively. No significant difference was found between bilateral sides.Conclusion:HC is located deeply and it is very difficult to expose it . Occipital condyle, jugular tubercle, jugular foramen and TPA are the main hindrances in the access to HC. Part 2 Surgical Aantomy of the hypoglossal canal andits adjacent structuresPurpose: To investigate the relationship of the nerves-vessel in the the hypoglossal canal (HC) and its adjacent structures for the further study of surgical approach in this area.Methods: The microsurgical anatomy of the extracranial muscles ,nerves and vessels in the Caniocervical junction region (CCJR) were investigated in 15 cadaveric head-neck specimens posterolaterally and anterolaterally, respectively. Then the transverse process of the atlas (TPA), jugular tubercle .occipital condyle and occipital squama were removed to observe the content of HC and the relationship of nerves and vessels within HC and between HC and its adjacent structures.Results:The main structures in the suboccipital area were vertebral artery (VA), venous plexu, occipital condyle and lateral mass. The length of the horizontal segment of VA in left and right side was 17.6+1.83mm and 18.2+ 1.39mm, respectively, and its vertical one was 16.2+ 1.01mm and 16.8+ 1.09mm, respectively. It gave rise to musclar branch (100%), neuro ramus one (53.3%) and posterior meningeal one (6. 7%)o TPA where VA turns from vertically to horizontally served as a much more useful anatomical landmark, with which many important structure could be identied, however , it was also one of big hindrances which blocked the access to the extracranial orifice of HC posterolaterally. The styloid diaphragm is an important landmark in the parapharyngeal space, which was subdivided into prestyloid and poststyloid compartments by the styloid diaphragm, hypoglossal nerve and other lower cranial nerves run between jugular vein and internal carotid artery in the poststyloidcompartment. There were two sites where hypoglossal nerve could be identied , the first one was the initial horizontal segment of the CN XII, which was 54 mm inferior to mastoi process tip , 11mm superior to bifurcation of common carotid artery, 25mm posterior to the angle of the mandible and where CN XII run under the sternocleidomastoid artery, the second one is the initial descending segment of CN XII, which was located 3 mm inferior to jugular foramen, where CN XII was adhered to CN X closely and couldn' t be seperated easily. The length of HC in left and right sides was 10.5 + 1. 3mm and 11.0+1. 5mm, respectively; it contained an venous plexus, the hypoglossal nerve, and a small pharyngeal ascending artery from behind to front, the venous plexus was the predominant constituent and run entire length of the canal and surrounded CN XII.The rootlets of CN XII emerged as a fan-shaped distribution and converged towards the intracranial orifice of HC(IOHC) in 2 bundles (66.7%), 3 bundles (30%) , 4 bundles (3.3%) . IOHC faced the brainstem and the distance of IOHC to jugular foramen in left and right sides was 14.4 + 0.97mm and 15.0 + 1.11mm, respectively. No significant difference was found between bilateral sides . Conclusion:TPA can serve as an important landmark in identifying some important structures in suboccipital area, however ,it is also a big handrance which blocks the access to extracranial orifice of HC posterolaterally. Hypoglossal nerve can be identified safely according to its features of either extracranial or intracranial part. The venous plexus of HC is a landmark to identify HC and aslo is a forecasting set preserving hypoglossal nerve.Purpose: To study the surgical approach for the dumbbell-shaped hypoglossal schwannoma in one-stage, simultaneously preserving the function of the important structures.Methods:The microsurgical anatomy and the exposure of the far-laterally trans-supracondylarotransverse process of atlas approach (FLTSCTPAA) were examined in 15 cadaveric head-neck specimens of adults,its exposing scale and advantages and disadvantages were studiedResults:A T-shaped skin incision is made behind mastoid process area, sternocleidomastoid muscle was detached and Henery interspace was exposed and the transverse process of the atlas could be touched and its adjacent structures(such as VA ) was identified ,the lateral muscule group was freeed one by one . The horizontal segment of the VA and posterior arch of C1 were exposured after the muscles forming the suboccipital triangle were detached.The transverse foramen of Cl was opened and the transverse process of Cl was resected, VA was displaced or not displased, the interspace between occipital condyle and jugular vein was freed and enlarged upward and downward and the paracondylar exposure was extended. A suboccipital craniectomy was made, the magnum foraman and posterior arch of C1 was also opened. The sigmoid sinus was unroofed up to jugular bulk. The hypoglossal canal was opened while the jugular tubercle was drilled off above the occipital condyle using condylar canal and jugular bulk as landmarks. We named the approach as FLTSCTPAA. It could be used to remove dumbbell-shaped hypoglossal schwannoma and both subdural and epidural hypoglossal schwannoma and any lesion in this area ,the craniectomy should be tailed individually according to the volum and location of the lesion so that the defect of the skull base can be minimized as possible as can. If the exposure was required to be extended up and anteriorly to jugular vein in some cases, it could be combined with transcervical approach or subtemporal fossa approach or the subtemporal and preauricular infratemporal approach.Conclusion: FLTSCTPAA can expose the entire length of and intracranial and extracranial openings of hypoglossal canal sufficiently and can be used to resect dumbbell-shaped hypoglossal schwannoma in one stage. The hearing and vestibular function is preserved and the stability of craniocervical junction region and the draining of jugular vein system are not destroyed and no retraction of brainstem is needed, therefore , it is a mininvasive approach. Objective :To improve the diagnosis and treatment of hypoglossal neurilemmoma (HGN).Methods : The data of 10 patients with HGN were retrospectively reviewed, of which 5 (early group) had been reported previously.A comparison of treatment strategy between early and latter group was made. Results:Typical hemiatrophy of the tongue presented in all 10 patients, hypoglossal canal could be showed in the bone window of CT , which , however ,might not confirm the existence of tumor if it is very small. MRJ was the optical choice for diagnosis. Among the early 5 cases with HGN which were all of dumbbell type , the intracranial part and the extracranial part of the tumor in 2 cases were removed stagedly which were removed by retromastoid approach and transcervical approach respectively while the one within the canal was not removed , 3 cases were operated via the far-lateral approach ,of which 1 was via transcondylar approach and 2 were via trans-supracondylar approach ; the 5 tumors were removed subtotally except 1 totally; CSF leakage and intracranial infection after operation occurred in 1 case ; the rating of Karnofsky Prognosis Scale was good in 4 cases and dead in 1 case. However, among the latter 5 cases, 4 cases including 2 of dumbbell type,l of intracranial type and 1 of intracanal type were operated via the modified far-lateral approach,of which 1 was via transcondylar approach and 3 were via trans-supracondylar approach ;and the tumor of extracranial type in the last case was resected twice via transcervical approach , being removed subtotally in the first operation followed by total removal with the aid of neuroavigation and nueroendoscope in the second operation when it failed to react to the treatment of gamma knife ;the 5 tumors were removed totally except 1 subtotally;all postoperative courses were uneventful.;follow up was performed successfully in 4 cases, the rating of Karnofsky Prognosis Scale was excellent in 3 cases and fair in 1 case. The outcomes of the latter 5 cases resected via modified approach were better than those of the early 5 cases.The modification of the far-lateral approach included muscles being freed following the interspace of muscles, and no or little of occipital condyle being drilled, and the hypoglossal canal being opened by drilling the jugular tubercle above occipital condyle in the cases with dumbbell type of the tumors,and the...