Extreme lateral transcondylar approach to the skull base.
In this study, the authors present their experience of using extreme later transcondylar approach (ELTC) for treating 7 patients with lesions in the anterolateral foramen magnum, upper cervical spine and cerebellopontine angle reaching upto jugular foramen. The tumours included meningiomas, neurofibromas (2 cases each), chondrosarcoma, epidermoid and aneurysmal bone cyst (one case each). The approach was used alone, in combination with retrolabyrinthine presigmoid approach in a patient with lower cranial nerve neurofibroma extending extracranially through the jugular foramen, or in combination with partial C1-C3 laminectomy in two patients with meningiomas situated anterolateral to the cord from the foramen magnum to C3. In two patients with extradural vertebral artery (VA) entrapment by a chondrosarcoma and aneurysmal bone cyst respectively, the vertebral artery was ligated distal to the tumour. The tumours were totally excised in five cases and partially in two. There was no preoperative mortality. The major complications included cerebrospinal fluid leak from the wound (3 cases) and increase in lower cranial nerve paresis (2 cases). At follow up, ranging from 6 months to 2 years, 5 patients showed no tumour recurrence. There was improvement in neurological status. One patient, with a partially excised aneurysmal bone cyst, showed no added deficits or increase in the tumour size. However, there was a massive regrowth in the patient with chondrosarcoma after 6 months. This technique provided a wide surgical exposure with direct visualization of the tumour-anterior cord interface, early proximal control of the VA and preservation of lower cranial nerves.
Lesions in the anterior foramen magnum, lower clivus, and the anterior aspect of upper cervical canal are difficult to access with the conventional techniques. A posterior cervical approach after laminectomy and suboccipital craniectomy is associated with morbidity due to neuraxial retraction and incomplete removal. The transoral approach has the disadvantage of working at a depth with vital cervicomedullary centres underneath, traversing the potentially infected oral cavity, CSF leak, limited lateral exposure and creation of instability.
The extreme lateral transcondylar approach (ELTC),,,,, provides a wide exposure anterior to the neuraxis and a good visualization of the tumour-cord interphase. If stabilization is required, it can be provided in the same sitting. We present our initial experience in the use of this approach in treating 7 patients with intra and extradural neoplasms of the foramen magnum-upper cervical spine.
Seven patients were operated via ELTC at Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, between March 1995 and December 1997. ELTC was combined with the retrolabyrinthine presigmoid approach in one patient and with the C1-C3 hemilaminectomy in two. The age of the patients ranged from 8 to 52 years (mean 33.4 years) and the male : female ratio was 3:4. The presenting symptoms have been summarised in Table I. The patients were investigated using plain and contrast CT scan with bone windows. Magnetic resonance imaging (MRI) was used to further define the extent of the lesion in three patients. Angiogram was done to delineate the anatomy of the VA. In both these cases, the VA was trapped above the tumour. The lesions included meningothelial and transitional meningioma arising from the dura of foramen magnum, (2 patients), lower cranial nerve neurofibromas (2 patients), cerebellopontine angle epidermoid, chondrosarcoma of the lateral mass of atlas, and C3 body and laminar aneurysmal bone cyst (one patient each respectively). The patient with C3 aneurysmal bone cyst had undergone previous partial decompression of the tumour by laminectomy.
Operative Technique : The operative technique for this procedure has been described earlier.,,,,
Patient positioning and monitoring : The patient is placed in a lateral position. Any rotation from a lateral position of the head causes C1 vertebra to move in relation to C2 vertebra leading to some displacement of the VA. The surgeon can operate from the head end or while positioned posterior to the patient. Intraoperative neurophysiological monitoring of somatosensory evoked potentials, brain stem auditory evoked responses and X, Xl and XI1 cranial nerves may be employed.
Skin Incision : This can be modified depending upon the need of the exposure [Figure 1]. A `C' shaped incision behind the mastoid going above the pinna and below upto midcervical region is used for a majority of the lesions; and especially when a presigmoid exposure is required. An `inverted L' shaped incision is employed when a cervical exposure is required. The same incision can be converted into a `reverse U' shaped incision when the posterior midline needs to be exposed to facilitate an occipitocervical stabilization in the midline.
Exposure of the suboccipital triangle : The muscles including sternocleidomastoid, splenius capitis, semispinalis capitis and superior fibres of levator scapulae are divided from their attachments and reflected antero inferiorly as depicted in [Figure 2] and described in detail by Sen and Sekhar and Al Mefty et al.,,, The transverse process of C 1 is easily palpable at this stage and forms the apex of the suboccipital triangle. The superior and inferior oblique muscles are identified at their attachment on the transverse process of C 1.,
Control of the vertebral artery : Using blunt dissection, the area filled with loose connective tissue caudal to the inferior oblique muscle and between C l and C 2 vertebra is dissected to identify the ventral ramus of C 2 nerve which runs transversely. The C 2 nerve is identified and followed laterally. Between the foramen transversarium of C l and C 2 vertebra the C 2 root crosses the vertical segment of the VA. Between C l and C 2 vertebra the VA can also be identified following the inferior border of inferior oblique muscle. The lateral mass of C l vertebra also serves as a landmark for the VA and is easily felt once the sternocleidomastoid is reflected from the mastoid process [Figure 3] The VA is exposed from foramen transversarium of C 2 vertebra to its entry into the dura mater. The perivertebral venous plexus overlies the VA and brisk venous bleeding is encountered before the VA is exposed. This is controlled by bipolar coagulation and packing with surgicel. Using a diamond drill, the transverse foramen of atlas, which transmits the VA is drilled to mobilize the vesse sacrificed.,
Bony drilling : If the tumour is mainly inhe posterior fossa extending down into the foramen magnum, a retromastoid craniectomy including the rim of the foramen magnum is performed. Mastoidectomy may be performed anteriorly upto the vertical segment of the VII nerve and posteriorly unroofing the lower half of the sigmoid sinus and the jugular bulb if a presigmoid exposure is required [Figure 4]. For intradural lesions, the sterior one-third to one-half of the occipital condyles and the lateral mass of C l are removed exposing atleast 1cm dura anterior to the entrance of the VA. During the condylar drilling, the jugular bulb and internal jugular vein , being in close proximity, require protection. For extradural tumours involving the occipital condyle, the entire condyle is resected following which an occipitocervical fusion becomes necessary. The hypoglossal nerve must be preserved after identifying the hypoglossal canal an When the tumour extends caudal to the rim of foramen magnum, the lateral aspect of the vertebrae from C l and below are exposed by dividing the muscles attached to the posterior tubercle of transverse process exposing the articular facets and adjacent portions of the lamina. The posterior arch and the posterior portion of the lateral mass of C 1 vertebra is drilled off to expose the lateral aspect of dura. Below C 1, the posterior two-thirds of the superior and inferior articular facets and the adjacent laminae of the vertebrae (depending on the longitudinal extent of the tumour) are drilled away exposing the lateral aspect of the thecal sac.
Dural opening and tumour removal : The dura is opened longitudinally. The dural entry of the VA is opened completely to mobilize it leaving a small cuff all around ito facilitate subsequent watertight closure of the sac. Removal of part of the occipital condyles and deroofing of the sigmoid sinus allows the lateral dura and VA to be reflected laterally, and enables visualization of the ventral foramen magnum [Figure 5] In case of anterior spinal extension, the spinal dura can also be opened longitudinally and the edges tented. The tumour is debulked and its capsule is dissected from the IX, X,Xl XII cranial and spinal nerves, the anterior surface of the brain stem and the spinal cord as well as the ipsilateral and contralateral VA. During capsular dissection from the lateral aspect, protection of the anterior spinal artery is required. In meningiomas, the ventral dural attachment of the tumour is coagulated after tumour removal [Figure 6].
Dural repair : The cuff around the VA facilitates watertight closure after tumour removal. If the dura is excised, autologous fascia lata and fat graft, adequate muscular closure and lumbar subarachnoid drain prevent cerebrospinal fluid leak.
Stabilization : Occipitocervical stabilization is required in cases when the occipital condyle with condylar surface of Cl lateral mass have been completely drilled off. If the retrosigmoid craniectomy is small, a lateral occipitocervical fusion may be directly performed using a contoured plate and bone graft. Alternatively, by exposing the midline occiput and upper cervical spine, a contoured reverse `U' rod can be fixed with sublaminar wiring and autologous bone grafting to achieve stabilisation.
Total excision of the tumour was performed in five patients. In patients with chondrosarcoma and aneurysmal bone cyst, only partial decompression was achieved. The surgery had to be staged in a patient with anterior foramen magnum meningothelial meningioma as there was bleeding from the marginal sinus and vertebral venous plexus during the bone work. The procedure was extradural in two patients. In three others, the dura was closed using a fat-fascia graft. When required, only partial excision of the occipital condyles and/or vertebral articular facets was performed, therefore, no stabilization was carried out.
There was no perioperative mortality in the series. There was CSF leak in 3 patients which was managed using continuous lumbar drainage and acetazolamide administration. The patients with cerebellopontine angle epidermoid and foramen magnum meningioma developed transient lower cranial nerve paresis.
The follow up ranged from six months to two years. All patients had an improved neurological status at follow up except the patient with chondrosarcoma of the lateral mass of atlas who showed reappearance of the partially decompressed lesion despite radiotherapy at follow up after 6 months. However, he refused further surgery and was subsequently lost to follow up. The other patient with the partially decompressed aneurysmal bone cyst of the lamina and body of C3 vertebra had improvement in hemiparesis after 6 months and has no further progression of symptoms at present.
The following case reports illustrate the applications of the approach and the problems encountered.
Case 1 : A 52-year old male patient presented with a history of bilateral upper limb paraesthesia and difficulty in carrying out fine movements with the right upper limb for the last 4 months. He developed restricted neck movements, progressive spastic quadriparesis, constipation and urinary frequency, numbness below neck and hoarseness of voice two months later. Neurological examination revealed left IX and X cranial nerve paresis with grade IV spastic quadriparesis, 25 to 50 % hypoaesthesia below C2, impaired posterior column sensations and restricted neck movements. His CT scan showed a hyperdense, enhancing mass extending from foramen magnum to upper border of C2 lamina. MRI revealed a hypointense mass on T1 becoming hyperintense on T2 weighted images [Figure 7] Using the ELTC approach, a well defined, firm, encapsulated tumour extending from foramen magnum to C2 lamina and arising from the lower cranial nerves was excised. Biopsy revealed a neurofibroma. Postoperatively, there was a transient increase in the lower cranial nerve paresis which required Ryle's tube feeding. His spasticity and weakness improved. At follow up after 2 years, the lower cranial nerve palsy had also improved and a repeat CT scan showed no residual tumour [Figure 7b].
Case 2 : A 37 year old woman presented with pain in the nape of neck of 10 years duration with progressive spastic quadriparesis for the last 2 years. On examination she had hypertonia with grade IV spastic quadriparesis, impaired posterior column sensations and restricted neck movements. MRI scan revealed an intradural extramedullary mass, isointense on both T1 and T2 weighted images extending from foramen magnum to C3, compressing the cord from the anterolateral aspect [Figure 8a]. An ELTC approach with excision of the posterior arch, transverse process and part of lateral mass of atlas and lamina, articular facet of C2 and part of C3 lamina was performed. During the bone work, there was brisk bleeding from the marginal sinus and the vertebral venous plexus due to which surgery was deferred. After a week, the wound was re-explored and a firm, vascular tumour situated anterior to the cord with a good arachnoidal plane and dural attachment was excised. Histopathology revealed a meningothelial meningioma. Postoperatively, there was CSF leak from the wound for which lumbar drainage and acetazolamide administration was required. A follow-up after six months revealed no deficits except terminal neck movement restriction. Contrast enhanced CT scan at follow up six months later showed complete excision of the meningioma [Figure 8b].
Case 3 : A 45 year old woman presented with headache, projectile vomiting, blurred vision for 6 months and decreased hearing from the left ear for 6 months. Neurological examination revealed only perception of light in the right eye due to mature cataract and a visual acuity of 6/36 with papilloedema in the left eye. She had left VII lower motor neuron paresis, VIII sensorineural deafness and X and XII nerve paresis. CT scan revealed an expanding lytic mass, isodense with multiple calcified specks, enhancing on contrast, in the right petroclival region and cerebellopontine angle extending extracranially through the jugular foramen [Figure 9a]. An ELTC approach in combination with retrolabyrinthine presigmoid approach was adopted. The left VA had an aberrant course with a hairpin loop from C2 to C1 foramen. A pale yellow, fibrous vascular tumour expanding the jugular foramen and emerging extracranially through it, was excised. On opening the dura, the lower cranial nerves were visualised and no intradural component of the lesion was seen. During excision of the tumour from the jugular bulb, there was bleeding from the jugular bulb which was controlled by muscle, gelfoam and surgicel application. Biopsy revealed a neurofibroma. Postoperatively, there were no symptoms of raised intracranial pressure. At follow up, after one and a half years, there was mild residual left VII, VIII and gross XII nerve paresis. Repeat CT scan revealed no residual lesion.
ELTC approach is useful for intradural mass lesions situated ventral to the cervicomedullary junction,, especially in recurrent tumours, where the arachnoidal plane between the tumour and the cervicomedullary junction has been lost and the capsular dissection carries the risk of injuring the neuraxis, cranial nerves, spinal roots and the anterior spinal artery., In these situations, while using the posterior approach, the base of the tumour located anterior to the cord may not be adequately visualized and thus, only partial tumour excision may be possible. Neurological deterioration may occur as access to the tumour may require division of some nerve roots and rotation of the cord. Vertebrobasilar aneurysms, arteriovenous malformations situated in the anterior cervicomedullary junction, extradural tumours involving the lower clivus/jugular foramen, developmental and rheumatoid lesions significantly involving the VA are also accessible by this approach. The advantages of ELTC approach, succinctly summarised by Sen and Sekhar include addressal of intradural lesions from lower clivus down to C5 by a single approach and from a lateral perspective which permits an excellent visualization of the tumour/neuraxial interface as well as cranial and spinal nerves. It allows an early proximal control of the VA and interruption of the blood supply to the tumour; and removal of the intra and extracanalicular part of dumbell neurofibromas and intra and extradural portions of meningioma in the same sitting. Since facets of the opposite side, vertebral bodies and the intervertebral discs are intact, the bone work does not lead to incipient stability. However, in case of complete condylar excision, an occipitocervical stabilization can be performed in the same sitting. ELTC approach can be combined with subtemporal-infratemporal or presigmoid petrosal approach to increase the exposure. In this series, the combination translabyrinthine approach was used for excision of a neurofibroma that had expanded the jugular foramen and emerged extracranially through it.
Extradural midline lesions can also be approached by the transoral,, and transmandibular or transmaxillary approaches., However, the transoral approach has the drawbacks of diiculty in reaching the laterally located lesions, the risk of CSF leak and infection from transgressing the contaminated oral cavity and the need for a separate procedure for stabilization and fusion. Moreover, the tumour-cord interface is not directly visualised.
The disadvantages of transcondylar approach include the potential for cerebrospinal fluid leak, lower cranial nerve paresis, vertebral artery injury and bleeding from the vertebral venous plexus. Three patients in the series had cerebrospinal fluid leak. In patients undergoing reoperations, the risk of cerebrospinal fluid leak increases. Babu et al recommend leaving a cuff of dura around the VA, during dural opening which can subsequently be sutured back to achieve a watertight closure. In this series, dural breach by tumour invasion or shrinkage was managed by a fascia lata-fat graft with continuous closed lumbar drainage and acetazolamide administration. The risk of developing IX to Xll cranial nerve paresis is also significant especially when the tumour capsule is enmeshed within the nerve fascicles. When a nerve is transected, an immediate reconstruction may be done since ELTC approach permits exposure of the extradural portion of the nerve as well. A hairpin loop of the VA was encountered in one patient in this study. The other anatomical variations of the VA in this region include an aberrant entry into the dura between Cl and C2, ossification of the ligament around the VA during its course on the arch of atlas forming a bony tunnel and sharp anteromedial turning of the VA around the arch of Cl. Thus, it is liable to be injured or occluded. Facilities and expertise for immediate arterial repair and reconstruction must be available especially if the VA is the dominant one or the patient develops symptoms of vertebrobasilar insufficiency, postoperatively. We encountered brisk bleeding from the vertebral venous plexus in one of the patients and from the jugular bulb in the other. In the former, due to excessive blood loss, further surgery had to be staged. In both the patients, the bleeding was controlled by the bipolar cautery and packing with muscle and surgicel.
None of our patients underwent an occipitocervical stabilization. This was because the extent of the occipital condylar resection was never more than one -third to one-half. However, in case the occipital condyle is completely excised in order to increase the exposure or when it is completely or bilaterally involved by the tumour, Al Mefly et al recommend an occipitocervical fusion using metal prosthesis and bone graft.
We admit that the patient with the cerebellopontine angle epidermoid could have been approached by the conventional retromastoid craniectomy. However `the white epidermoid' had an unusual computed tomographic and magnetic resonance imaging picture and we preoperatively misdiagnosed the lesion as a meningio or a neurofibroma.
To conclude, ELTC approach offers an excellent visualization of the ventral dural space in the high cervical spine and foramen magnum region. However, the extensive soft tissue dissection, meticulous bony drilling, requirement pertise for vascular anastomosis and prolonged used for resection of lesions situated ventral to the cervicomedullary junction, especially the recurrent which the conventional posterior approaches do not provide adequate exposure.