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COMMENTARY
Year : 2016  |  Volume : 64  |  Issue : 3  |  Page : 462-464

Far lateral approach: Orientation and planning


Department of Neurosurgery, Fortis Hospital, Mohali, Punjab, India

Date of Web Publication3-May-2016

Correspondence Address:
Ashis Pathak
Department of Neurosurgery, Fortis Hospital, Mohali, Punjab
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0028-3886.181565

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How to cite this article:
Pathak A. Far lateral approach: Orientation and planning. Neurol India 2016;64:462-4

How to cite this URL:
Pathak A. Far lateral approach: Orientation and planning. Neurol India [serial online] 2016 [cited 2019 Aug 17];64:462-4. Available from: http://www.neurologyindia.com/text.asp?2016/64/3/462/181565


The approach to lesions located anterior or anterolateral to the neuraxis around the foramen magnum is always a challenge which demands for careful planning based on the understanding of the complex anatomical relationship of the related structures. Common lesions in this location may include tumours (e.g., meningioma, chordoma, chondroma, dermoid or aneurysms of vertebral artery) anywhere in its location, up to the vertebro-basilar junction. The maximum advantage from this approach is based on an exact positioning, a precise incision, systematic dissection of musculoskeletal structures and avoidance of damage to vascular and neural elements which come in the way of accessing the lesion in question.

The term 'far lateral approach' is an umbrella term which encompasses the different extents to which the surgical trajectory may be fashioned depending on the depth and location of the lesion. The origin of the term came from the concept of 'lateral subocciptal approach' intended to expose the area behind the sternocleidomastoid muscle, the vertebral artery and the medial aspect of the atlanto-occipital joint. However, the far lateral exposure is subdivided into: (a) Transcondylar approach for lesions in the clival/perimedullary area; (b) supracondylar approach for gaining access to the region medial to the jugular tubercle; and, (c) paracondylar approach to access the region posterior and lateral to jugular foramen.[1] 'Extreme lateral approach' is a commonly used term,[2] similar to the paracondylar exposure, intended for exposure of the deep area located anterior to the vertebral artery and the sternocleidomastoid origin but behind the jugular bulb. This approach, along with condylar drilling, can provide a good access even to the contralateral extradural space anterior to the cervico-medullary junction and also to the lower clivus.[3]

Though the localization of a lesion is defined on a MRI scan yet it may be better to supplement it with a CT scan for delineation of the bony morphology of the region. In addition, the disposition of the veretebral artery and the dominance of the venous sinuses need to be studied thoroughly through angiographic studies before making the final plan of approach for resection.

The anaesthetic considerations include special attention to avoid any venous compression in the neck while positioning the patient; and, keeping a patent airway using a flexo-metallic tube. Electrophysiological monitoring in terms of somatosensory and auditory evoked potential studies are important tools as they predict any further compression or insult to the neural structures during the time of positioning of the patient as well as during the intra-operative handling of the spinal cord. Moreover, monitoring of the lower cranial nerve function is of distinct advantage in order to avoid any serious morbidity. Meticulous blood pressure monitoring is essential to avoid ischemia to neural structures and all precautions for avoiding intra-operative deep venous thrombosis (DVT) are taken by using the DVT compression stockings.

The extent of exposure and access revolves around the area between the tip of the mastoid process, the ipsilateral lateral arch of C1 and the adjoining occipital condyle. The first important step of the exposure begins with positioning of the patient. This has to be done very carefully in order to open up the space between the occiput and lateral aspect of neck. Care has to be taken so that there is not too much of flexion of the neck which may aggravate the already existing compression of the spinal cord by the mass lesion in the region of foramen magnum. Though the sitting position may have some advantages in view of achieving a good venous drainage and a clearer field, its use is restricted to neurosurgeons who are routinely accustomed to it. The retro-mastoid incision can be in the form of a 'large C' or a 'lazy S' following which the muscles are split up to the sternocleidomastoid attachment. Subsequently, the muscles attached to the occiput and the C 1 arch in the posterior triangle are dissected.

The isolation of the vertebral artery remains the highlight of this approach as it may have anatomical variations in its course and may be involved by the lesion also.[4] The compounding factor is the conglomeration of veins of the surrounding venous plexus which forms a vascular sheath around the vertebral artery making its identification difficult and the dissection through a vascular field. This can be achieved by clearing the transverse process of C1 of its muscular attachments, removing the bone of the foramen transversarium encircling the artery and gently hooking the artery from its position. The exposed vertebral artery is next separated from the capsule of the occipito-C1 joint. The sheath of venous plexus is incised along the length of the artery taking care of the bleeding and the artery is traced up to its dural entry. Any difficulty in locating the vertebral artery can be solved by opening the dura mater and tracing the vessel in a retrograde fashion from its entry point. The mobilization of the vertebral artery facilitates the drilling of the occipital condyle and the jugular tubercle when deemed essential.

The bony exposure is tailored to the anatomical disposition of the lesion. The need for drilling of the occipital condyle is definitely indicated for lesions situated purely in the anterior midline in order to avoid any retraction to neural structures. Condylar drilling is also essential for lesions involving the condyle itself e.g., chondrosarcomas or chondromas. Otherwise, for antero-laterally disposed lesions, the displacement of the cervicomedullary junction creates a corridor for an easy access without the need to sacrifice any condylar element. This is because the eccentric enlargement of the lesion displaces the spinal cord or cervico-medullary junction postero-laterally creating an easy access for resection. For tumors extending downwards from the craniovertebral junction into the cervical canal, removal of the lateral arch of C1 might not be sufficient. Accessing this inferior extension of the tumor may necessitate a hemi-laminectomy of the ipsilateral C2 or C3 vertebrae according to the extent of the lesion.

A linear incision is given over the dura behind the sigmoid sinus and the vertebral artery and the opened dural edges are kept retracted with hitch stitches. In an anterolaterally disposed tumour, it is expected that the lesion which is found draped by the arachnoid membrane and the cranial nerves, would be encountered immediately after dural and arachnoidal opening. In tumours strictly restricted to midline, the dentate ligaments may have to be incised in order to create an adequate working space for introduction of micro-instruments to avoid injury to cranial nerves, which may be manipulated or caught in the suction during dissection of the tumor through a narrow operative corridor.

After excision of the lesion, closure of the dura might not be always possible in a watertight fashion because of shrinkage of the dural margins. The use of a fat graft or a small muscle patch along with dural substitute might be ideal to seal the rent. This should be followed by a good water tight muscle closure.

The 'extreme lateral approach' is described for lesions extending above the jugular foramen and lower clivus. In this exposure, the bone below the jugular bulb is drilled taking care that the bony excision does not extend up to the hypoglossal canal. The entry of the vertebral artery into the dura is exposed. This definitely makes excision of lesions located in the region of the lower clivus convenient.

Post operative care aims at early mobilization of the patient. In case of any bulge of the wound or suspicion of cerebrospinal fluid leak, a lumbar drainage should be instituted. Nasogastric tube feeding may be a necessity in cases of lower cranial nerve neuropathy. In case of established serious injury to the lower cranial nerves, a feeding jejunostomy may be the long term solution. Incomplete excision of a lesion demands a follow up imaging at regular intervals; and, consideration of radiosurgery in case a neoplastic lesion, with tendency to recur, is present.

To conclude, the far lateral approach and its variations provide a precise and direct approach to lesions in close proximity to or involving the lower clivus and the craniovertebral junction. It avoids the chances of contamination of wound (that is a distinct possibility when approaching the lesion through the endonasal or transoral approach), risk of cerebrospinal fluid leak, and limitations of the lateral exposure encountered in a midline transoral approach. Moreover, it provides an excellent visual access to lesion-neural interface, which promotes the chances of a safe dissection with minimal morbidity. However, the actual requirement of these approaches have to be weighed carefully after a detailed study of the anatomy which may be distorted by the lesion. There may also be normal variations of anatomy in this region. The findings of the study in focus [5] have also been observed and affirmed by experienced neurosurgeons. Thus, many of the lesions located in the foramen magnum region can be safely excised without excision of the occipital condyle.[6]

 
  References Top

1.
Wen HT, Rhoton AL Jr., Katsuta T, de Oliveira E. Microsurgical anatomy of the transcondylar, supracondylar, and paracondylar extensions of the far-lateral approach. J Neurosurg 1997;87:555-85.  Back to cited text no. 1
    
2.
Sen CN, Sekhar LN. An extreme lateral approach to intradural lesions of the cervical spine and foramen magnum. Neurosurgery 1990;27:197-204.  Back to cited text no. 2
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3.
Kawashima M, Tanriover N, Rhoton AL Jr., Ulm AJ, Matsushima T. Comparison of the far lateral and extreme lateral variants of the atlanto-occipital transarticular approach to anterior extradural lesions of the craniovertebral junction. Neurosurgery 2003;53:662-74.  Back to cited text no. 3
    
4.
Liu JK, Couldwell WT. Far-lateral transcondylar approach: surgical technique and its application in neurenteric cysts of the cervicomedullary junction. Report of two cases. Neurosurg Focus 2005;19:E9.  Back to cited text no. 4
    
5.
Mohammad HR, Vooturi S, Panigrahi M. Far lateral approach: Is condylar resection required? Neurol India 2016;64:454-60.  Back to cited text no. 5
    
6.
Nanda A, Vincent DA, Vannemreddy PS, Baskaya MK, Chanda A. Far-lateral approach to intradural lesions of the foramen magnum without resection of the occipital condyle. J Neurosurg 2002;96:302-9.  Back to cited text no. 6
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