Microsurgical and magnetic resonance imaging anatomy of the cerebello-medullary fissure and its application during fourth ventricle surgery.

The cerebellomedullary fissure, the only entrance or exit to the fourth ventricle, is surrounded rostrally by the cerebellar tonsils and the biventral lobules and caudally by the medulla oblongata, the tela choroidea, and the lateral recesses. This fissure is an important route in operations on the fourth ventricle. We studied the microsurgical and magnetic resonance imaging (MRI) anatomy of the fissure by using autopsied normal cerebellum. MRI revealed that the fissure is visible as a slit and is indicated by the enhanced choroid plexus and the flocculus. Oriented by the anatomical information thus obtained, we have surgically treated nine patients with a tumor either in or around the fourth ventricle. Preoperative MRI clearly demonstrated the tumors in relation to the cerebellomedullary fissure. It revealed the precise anatomical location and extension of the tumor, not only its inferior extension but also its lateral one. The MRI findings and microsurgical anatomy of the cerebellomedullary fissure were quite useful for the removal of the tumors in the fourth ventricle.     

The midline suboccipital subtonsillar approach to the hypoglossal canal: surgical anatomy and clinical application

Summary Primary lesions of the hypoglossal canal, such as hypoglossal schwannomas, are rare. No consensus exists with regard to the surgical approach of choice for treatment of these lesions. Usually, lateral transcondylar approaches have been used. The authors describe the surgical anatomy of the midline subtonsillar approach to the hypoglossal canal. This approach includes a midline suboccipital craniotomy, dorsal opening of the foramen magnum and elevation of ipsilateral cerebellar tonsil to expose the hypoglossal nerve and its canal. The midline subtonsillar approach permits a straight primary intradural view to the hypoglossal canal. There is no necessity of condylar resections. The surgical anatomy of the subtonsillar approach is described and illustrated by an example of a case.     

Transcerebellomedullary fissure approach with special reference to methods of dissecting the fissure

OBJECT: The purpose of the present study was to refine the transcerebellomedullary fissure approach to the fourth ventricle and to clarify the optimal method of dissecting the fissure to obtain an appropriate operative view without splitting the inferior vermis. METHODS: The authors studied the microsurgical anatomy by using formalin-fixed specimens to determine the most appropriate method of dissecting the cerebellomedullary fissure. While dissecting the spaces around the tonsils and making incisions in the ventricle roof, the procedures used to expose each ventricle wall were studied. Based on their findings, the authors adopted the best approach for use in 19 cases of fourth ventricle tumor. The fissure was further separated into two slit spaces on each side: namely the uvulotonsillar and medullotonsillar spaces. The floor of the fissure was composed of the tela choroidea, inferior medullary velum, and lateral recess, which form the ventricle roof. In this approach, the authors first dissected the spaces around the tonsils and then incised the taenia with or without the posterior margin of the lateral recess. These precise dissections allowed for easy retraction of the tonsil(s) and uvula and provided a sufficient view of the ventricle wall such that the deep aqueductal region and the lateral region around the lateral recess could be seen without splitting the vermis. The dissecting method could be divided into three different types, including extensive (aqueduct), lateral wall, and lateral recess, depending on the location of the ventricle wall and the extent of surgical exposure required. CONCLUSIONS: When the fissure is appropriately and completely opened, the approach provides a sufficient operative view without splitting the vermis. Two key principles of this opening method are sufficient dissection of the spaces around the tonsil(s) and an incision of the appropriate portions of the ventricle roof. The taenia(e) with or without the posterior margin of the lateral recess(es) should be incised.     

Choroid plexus papilloma presenting with cerebrospinal fluid rhinorrhea and otorrhea: case report

A 52-year-old woman presented with right rhinorrhea and right otorrhea manifesting as aural fullness for 2 years caused by a choroid plexus papilloma in the right cerebellomedullary cistern. Computed tomography and magnetic resonance imaging revealed a well defined lobulated mass at the foramen of Luschka, which extended towards the right cerebellomedullary cistern with slight dilation of the ventricular systems. The tumor was totally resected via a right lateral suboccipital approach. Histological examination revealed a choroid plexus papilloma. Postoperative course was uneventful, just after the operation rhinorrhea ceased completely, and hearing of the right ear dramatically improved. Choroid plexus papillomas rarely cause cerebrospinal fluid (CSF) rhinorrhea. Total removal of the tumor resulted in the cessation of CSF leaks.     

Telovelar approach to the fourth ventricle: microsurgical anatomy

OBJECT: In the past, access to the fourth ventricle was obtained by splitting the vermis or removing part of the cerebellum. The purpose of this study was to examine the access to the fourth ventricle achieved by opening the tela choroidea and inferior medullary velum, the two thin sheets of tissue that form the lower half of the roof of the fourth ventricle, without incising or removing part of the cerebellum. METHODS: Fifty formalin-fixed specimens, in which the arteries were perfused with red silicone and the veins with blue silicone, provided the material for this study. The dissections were performed in a stepwise manner to simulate the exposure that can be obtained by retracting the cerebellar tonsils and opening the tela choroidea and inferior medullary velum. CONCLUSIONS: Gently displacing the tonsils laterally exposes both the tela choroidea and the inferior medullary velum. Opening the tela provides access to the floor and body of the ventricle from the aqueduct to the obex. The additional opening of the velum provides access to the superior half of the roof of the ventricle, the fastigium, and the superolateral recess. Elevating the tonsillar surface away from the posterolateral medulla exposes the tela, which covers the lateral recess, and opening this tela exposes the structure forming the walls of the lateral recess.     

不同解剖入路显露颈静脉孔区的定量研究

目的定量研究枕下远外侧入路及耳后经颞入路对颈静脉孔区的显露程度,为临床个体化选择手术入路、保护重要结构功能提供可靠的解剖依据。方法选择经10％福尔马林固定的成人头颈湿标本各12具（24侧）,采用枕下远外侧入路及耳后经颞入路进行解剖学研究,用脑立体定向仪测定各步骤颈静脉孔区的显露面积,用游标卡尺测量斜坡和三叉神经的显露长度。结果在远外侧入路中,磨除颈静脉突、部分磨除枕髁后对颈静脉孔区显露程度显著增加;在耳后经颞入路中,迷路后入路、部分磨除迷路对颈静脉孔区的显露程度显著增加。结论磨除颈静脉突是枕下远外侧入路显露颈静脉孔的关键;迷路下入路和部分磨除迷路入路是自侧方显露颈静脉孔区的理想手术入路。     

Endoscopic opening of the foramen of magendie using transaqueductal navigation for membrane obstruction of the fourth ventricle outlets. Technical note

A membrane obstruction of the foramina of Magendie and Luschka is an uncommon origin of hydrocephalus characterized by unusual clinical symptoms of rhomboid fossa hypertension. Various surgical approaches have been proposed to alleviate this obstruction, including opening the obstructed foramen of Magendie using suboccipital craniectomy, shunting procedures, and more recently, endoscopic third ventriculostomy (ETV). In some cases, however, reshaping of the posterior fossa due to the collapse of the prepontine cistern could make ETV difficult for the surgeon and dangerous to the patient. In these cases, endoscopic opening of the foramen of Magendie by transaqueductal navigation of the fourth ventricle is a suitable and feasible therapeutic option.     

Telovelar approach to the fourth ventricle: operative findings and results in 16 cases

Summary Background. The cerebellomedullary fissure as a corridor for exposure of the fourth ventricle without vermian splitting is enjoying increasing application as a technique for exposure, to avoid the complications related to vermian splitting. The purpose of this study is to describe the operative findings and the results in 16 fourth ventricular tumours removed via telovelar approach. The impact of the pathological nature of the lesion on the degree of tumour removal is also discussed.Methods. Telovelar approach to the fourth ventricle was used in 16 consecutive patients. The charts were reviewed retrospectively. The pathological changes in the tela choroidea and inferior medullary velum, degree of tumour removal, and the clinical outcome are described.Findings. The tela choroidea was thinned out and streched over the tumour surface in 10 cases (large tumours). In epidermoid and dermoid cysts (3 cases), the tela choroidea was amalgamated with the tumour capsule. The inferior medullary velum was infiltrated by the tumour and was not detected as a separate layer in 6 cases (3 cases vermian astrocytomas and 3 cases medulloblastomas). The inferior medullary velum was thinned out and stretched as a neural tissue sheet over the tumour surface in 10 cases (4 ependymomas, 2 meningiomas, 2 epidermoids, one dermoid and one choroid plexus papilloma). Total removal was achieved in 11 out of 16 patients (68.75%). Subtotal removal was achieved in the remaining patients (31.25%); three ependymomas, one medulloblastoma, and one anaplastic astrocytoma. Cerebellar mutism was not observed in any patient and there was no mortality.Interpretation. Despite the panoramic view provided by the telovelar approach, the pathological nature of the lesion and vital neural tissue infiltration are limiting factors for total tumour removal. Total removal of tumours focally attached to critical areas in the fourth ventricle should not be attempted at the expense of patients morbidity and mortality. To achieve optimum outcome, near total excision is acceptable in cases where complete removal may endanger function or life.     

Transcerebellomedullary fissure approach to lesions of the fourth ventricle: less is more?

Background

The transcerebellomedullary fissure (trans-CMF) approach is safe and effective. Nevertheless, previous research documented a few differences in the use of this approach with regard to the opening portion of the fissure and roof of the ventricle. Here, we present a series of patients with fourth ventricular lesions and our experience using the trans-CMF approach.

Methods

Fifty patients who underwent the trans-CMF approach were analyzed. The tela choroidea was simply incised in 32 patients: 27 unilaterally and 5 bilaterally. Both the tela and inferior medullary velum were cut in 18 patients: 16 unilaterally and 2 bilaterally. Unless the tumor extended below the C1 level, C1 was preserved intact. Brainstem mapping (BSM) and corticobulbar tract (CBT) motor-evoked potential (MEP) monitoring were used.

Results

Gross total removal was achieved in 41 (82 %) cases, and sub-total removal was achieved in 9 (18 %) cases. Two deaths occurred 1–2 months postoperatively because of pulmonary complications. Four patients developed temporary mutism, all of whom underwent the bilateral trans-CMF approach (this rate is significantly higher than that of the unilateral approach, P?<?0.05). No permanent neurological deficit occurred.

Conclusion

The trans-CMF approach provides excellent access to fourth ventricular lesions without splitting the vermis. The opening portion of the fissure and roof of the ventricle should be determined by the location, extension and size of the lesion. In most cases, the unilateral trans-CMF approach with only a tela choroidea incision is adequate; this procedure is mini-invasive and possibly prevents postoperative mutism.     

Surgery on anterior foramen magnum meningiomas using a conventional posterior suboccipital approach: a report on an experience with 17 cases.

OBJECTIVE: The advantages of a posterior "conventional" suboccipital approach with a midline incision over lateral, anterolateral, and anterior approaches to anteriorly placed foramen magnum meningiomas are discussed. METHODS: From 1991 to March 2000, 17 patients with foramen magnum meningiomas arising from the anterior or anterolateral rim of the foramen magnum underwent operations in the Department of Neurosurgery at King Edward Memorial Hospital and Seth G.S. Medical College. All patients were operated on in a semi-sitting position by use of a conventional suboccipital approach with a midline incision and extension of the craniectomy laterally toward the side of the tumor up to the occipital condyle. RESULTS: The patients ranged in age from 17 to 72 years, and the tumors ranged in size from 2.1 to 3.8 cm. The intradural vertebral artery was at least partially encased on one side in eight patients and on both sides in two patients. The brainstem was displaced predominantly posteriorly in each patient. A partial condylar resection was performed in two cases to enhance the exposure. Total tumor resection was achieved in 14 patients, and a subtotal resection of the tumor was performed in the other 3 patients. In one patient, a small part of the tumor was missed inadvertently, and in the other two patients, part of the tumor in relation to the vertebral artery and posterior inferior cerebellar artery was deliberately left behind. After surgery, one patient developed exaggerated lower cranial nerve weakness. There was no significant postoperative complication in the remainder of the patients, and their conditions improved after surgery. The average length of follow-up is 43 months, and there has been no recurrence of the tumor or growth of the residual tumor. CONCLUSION: From our experience, we conclude that a large majority of anterior foramen magnum meningiomas can be excised with a lateral suboccipital approach and meticulous microsurgical techniques.     

Lateral suboccipital approach for vertebral and vertebrobasilar artery lesions

A modification of the unilateral suboccipital approach is elaborated and illustrated. This modification is useful for aneurysms of the vertebral artery, the vertebrobasilar junction, and the proximal basilar trunk, and for arteriovenous malformations of the inferolateral cerebellum. It entails extreme lateral removal of the rim of the foramen magnum toward the condylar fossa and posterolateral removal of the arch of the atlas toward the exposed vertebral artery. This extra bone removal allows an approach to the front of the brain stem from inferolaterally, after gentle upward and medial retraction of the tonsil, with minimal or no retraction of the medulla.     

Adult choroid plexus papilloma of the posterior fossa: extraventricular location

Choroid plexus papillomas (CPPs) are rare neuroectodermal neoplasms accounting for 0.4% of all intracranial neoplasms in adults. Most of them are located in the posterior fossa in adults. Although CPPs commonly arise from the 4th ventricle, they occasionally extend to extraventricular space. Furthermore some occur primarily in the extraventricular region. It is difficult to diagnose CPP preoperatively when the main portion of the tumor is not located in the 4th ventricle. We present a case of a 54-year-old male manifesting slurred speech, nystagmus and cerebellar ataxia. Magnetic resonance imaging demonstrated an intracerebellar solid tumor with multilocular cysts, extending towards both the right lateral medullary region and the foramen of Luschka. Computed tomography scans showed patchy calcification at the periphery of the solid component. Angiographically, via the right posterior inferior cerebellar artery revealed the tumor was faintly opacified. Preoperative diagnosis included meningiomas, low-grade astrocytomas, ependymomas or CPPs, but none of them had neuroradiologically decisive findings. Tumor was subtotally resected through a right suboccipital craniectomy. A calcified solid portion adhering to the lower cranial nerves was left unresected. The pathological finding was CPP. CPP should be considered among calcified and enhanced masses in the lateral medullary to cerebellopontine angle space in adults, even if the main portion of the tumor is not located in the 4th ventricle.     

3D Computer graphics simulation to obtain optimal surgical exposure during microvascular decompression of the glossopharyngeal nerve

The affected artery in glossopharyngeal neuralgia (GPN) is most often the posterior inferior cerebellar artery (PICA) from the caudal side or the anterior inferior cerebellar artery (AICA) from the rostral side. This technical report describes two representative cases of GPN, one with PICA as the affected artery and the other with AICA, and demonstrates the optimal approach for each affected artery. We used 3D computer graphics (3D CG) simulation to consider the ideal transposition of the affected artery in any position and approach. Subsequently, we performed microvascular decompression (MVD) surgery based on this simulation. For PICA, we used the transcondylar fossa approach in the lateral recumbent position, very close to the prone position, with the patient’s head tilted anteriorly for caudal transposition of PICA. In contrast, for AICA, we adopted a lateral suboccipital approach with opening of the lateral cerebellomedullary fissure, to visualize better the root entry zone of the glossopharyngeal nerve and to obtain a wide working space in the cerebellomedullary cistern, for rostral transposition of AICA. Both procedures were performed successfully. The best surgical approach for MVD in patients with GPN is contingent on the affected artery—PICA or AICA. 3D CG simulation provides tailored approach for MVD of the glossopharyngeal nerve, thereby ensuring optimal surgical exposure.     

Foramen magnum meningioma and arachnoid cyst coinciding in the lateral cerebellomedullary cistern--case report.

An extremely rare foramen magnum meningioma associated with an arachnoid cyst in the lateral cerebellomedullary cistern occurred in a 65-year-old female presenting with dizziness. Neuroimaging revealed a meningioma at the left lateral edge of the foramen magnum and an arachnoid cyst mainly located in the right lateral cerebellomedullary cistern, compressing the medulla oblongata bilaterally. After fenestration of the cyst wall and tumor removal, the clinical symptoms ameliorated. We recommend that where a foramen magnum tumor coexists with an arachnoid cyst of the posterior fossa, the tumor should be removed after shrinking the cyst to obviate the need for brainstem retraction.     

Surgical approach to the fourth ventricle cavity through the cerebellomedullary fissure

Lesions of the fourth ventricle represent a challenge to neurosurgeons because of severe deficits that occur following injury to the delicate structures in the ventricle wall and floor. The conventional approach to the fourth ventricle is by splitting the vermis on the suboccipital surface of the cerebellum. In the last 9 years, a series of 21 patients in our clinic underwent microsurgical tumor resection by the unilateral transcerebellomedullary fissure approach. The patients had various pathologies including hemangioblastoma, epidermoid tumor, medulloblastoma, ependymoma, low grade astrocytoma, choroid plexus carcinoma, choroid plexus papilloma, adenocarcinoma in the pons, and cavernoma in the medulla. Total removal was achieved in all but three cases. One death occurred 2 months after surgery due to pulmonary complication. In the follow-up period of 2 months to 5 years, the preoperative symptoms disappeared in all cases except one with a brainstem lesion. By a unilateral transcerebellomedullary fissure approach, it is possible to provide sufficient operative space from aqueduct to obex without splitting the vermis. This approach needs meticulous dissection of the fissure and preservation of the posterior inferior cerebellar artery and its branches.     

Trans-cerebellomedullary fissure approach with special reference to lateral route

The trans-cerebellomedullary fissure (CMF) approach provides good exposure of the fourth ventricle without splitting the inferior vermis. The popularly utilized trans-CMF approach is performed in the midline suboccipital approach. However, the trans-CMF approach actually has two routes: medial and lateral. The lateral route is the trans-CMF approach through a lateral foramen magnum approach such as the transcondylar approach, opening the CMF from the lower unilateral side. We studied the surgical anatomy of the CMF and fourth ventricle. Based on the anatomic findings, we adopted the lateral route of the trans-CMF approach for four patients, each with a tumor near the jugular tubercle extending into the fourth ventricle through the CMF. Our study demonstrated that the lateral route of the trans-CMF approach enables sufficient exposure of not only unilateral cerebellopontine cistern but also of the lateral part of the fourth ventricle. A tumor is safely removed by this approach with easy feeder or tumor bed controls, especially if it is anchored at the lateral part of the CMF as is the jugular tubercle meningioma.     

经小脑延髓裂入路显微手术切除儿童第四脑室肿瘤

目的 报道经小脑延髓裂入路显微外科手术切除儿童第四脑室肿瘤的临床疗效。方法 采用枕下正中切口、小脑延髓裂入路在手术显微镜下切除第四脑室肿瘤18例。结果 手术治疗18例，其中肿瘤全切除13例，近全切除5例。术后无l例出现小脑性缄默综合征。出现脑积水3例，2例经行侧脑室．腹腔分流后好转，l例因急性梗阻性脑积水死亡。结论 经小脑延髓裂入路，不需切开小脑蚓部，可避免损伤正常小脑组织，应用显微外科技术有助切除第四脑室肿瘤，提高手术疗效。     

Subtonsillar-transcerebellomedullary approach to lesions involving the fourth ventricle, the cerebellomedullary fissure and the lateral brainstem

We describe the use of the subtonsillar-transcerebellomedullary approach to laterally placed fourth ventricle and brain-stem lesions. The subtonsillar-transcerebellomedullary approach to the fourth ventricle and the lateral brainstem was used in six patients: three patients with tumours of the fourth ventricle and brainstem (two ependymomas and one papillary thyroid carcinoma metastasis), two patients with cavernous angiomas of the brainstem and one patient with a distal posterior inferior cerebellar artery (PICA) aneurysm. The microsurgical anatomy of this approach was studied in five cadaveric head specimens. The tumours and cavernous angiomas were removed and the distal PICA aneurysm was clipped successfully. In all patients the Karnofsky performance scale (KPS) was equal to or better than the preoperative status on follow-up examinations. The anatomical studies also revealed the extensive exposure provided with this approach. The subtonsillar-transcerebellomedullary approach is recommended for lesions occupying the cerebellomedullary fissure, and the lateral aspect of the fourth ventricle.     

第四脑室肿瘤的显微外科治疗

目的探讨第四脑室肿瘤手术入路和显微手术技巧,以提高第四脑室肿瘤的手术疗效。方法84例第四脑室肿瘤患者,行显微镜下切除肿瘤、后颅窝骨瓣成形及复位术。其中,61例采用正中孔-小脑蚓部入路,19例采用小脑延髓裂入路,4例取正中孔-小脑蚓部与小脑延髓裂联合入路。术前行侧脑室外引流4例,术中行侧脑室-枕大池分流3例,术后行侧脑室外引流术1例。结果本组全切除肿瘤63例(75.0%),次全切除21例(25.0%),无手术死亡病例。术后并发症:上消化道出血6例,小脑缄默症2例,四脑室血肿1例,脑积水1例,颅神经功能障碍1例。随访82例,平均38.4个月,死亡9例。结论术前正确判断肿瘤性质及其基底部所在位置,选择适宜的手术入路,熟练应用显微外科技术,是手术成功治疗的第四脑室肿瘤关键。     

Endoscopic far-lateral approach to the posterolateral craniovertebral junction: an anatomical study

Minimally invasive surgery to the posterolateral craniovertebral junction (CVJ) has not been sufficiently described. The aims of this study were to evaluate the feasibility of an endoscopic far-lateral approach to the posterolateral craniocervical junction and to better understand the related anatomy under distorted endoscopic view. Ten fresh cadavers were studied with 4-mm 0° and 30° endoscopes to develop the surgical approach and to identify surgical landmarks. After making a 3-cm straight incision behind the mastoid process, the superior oblique and rectus capitis posterior major muscles were partially exposed. An endoscope was then introduced and the two muscles were followed inferiorly until the posterior arch of the atlas appeared. The two muscles were removed to create ample working space without violating the posterior atlanto-occipital membrane. The vertebral artery was identified by the landmark of the posterior arch of the atlas, and the atlanto-occipital joint and foramen magnum were exposed. In addition to suboccipital craniectomy, transcondylar, supracondylar, and paracondylar extension by drilling were applicable through the narrow corridor under superb visualization. The intradural neurovascular structures from the acousticofacial bundle to the dorsal root of C2, anterolateral space of the foramen magnum, cerebellomedullary fissure, and fourth ventricle were clearly demonstrated. This endoscopic far-lateral approach offers excellent exposure of surgical landmarks around the posterolateral CVJ with minimal invasiveness. Endoscopic soft tissue dissection is key to creating the surgical corridor. This approach could offer an alternative to the conventional far-lateral approach in selected cases.