Anterior retropharyngeal approach to the cervical spine.
The anterior retropharyngeal approach (ARPA) accesses anteriorly situated lesions from the clivus to C3, in patients with a short neck, Klippel Feil anomaly or those in whom the C2-3 and C3-4 disc spaces are situated higher in relation to the hyoid bone and the angle of mandible where it is difficult to approach this region using the conventional anterior approach, due to the superomedial obliquity of the trajectory. The ARPA avoids the potentially contaminated oropharyngeal cavity providing for a simultaneous arthrodesis and instrumentation during the primary surgical procedure. Experience of five patients with high cervical extradural compression, who underwent surgery using this approach between 1994 and 1999, is presented. The surgical procedures included excision of ossified posterior longitudinal ligament (n=2); excision of prolapsed disc and osteophytes (n=2); and excision of a vertebral body neoplasm (n=1). Following the procedure, vertebral arthrodesis was achieved using an iliac graft in all the patients. Only one patient with vertebral body neoplasm required an additional anterior cervical plating procedure for stabilisation the construct. The complications included transient respiratory insufficiency and neurological deterioration in two patients; and, pharyngeal fistula and donor site infection in one patient.
The conventional transoral approach traversing the midline pharyngeal raphe,[1-3] and the anterior cervical approach through the avascular plane between the carotid sheath and trachea and oesophagus,,,, are adequate to approach the upper (C1-2) and middle cervical vertebral segments (C3) respectively. However, when an approach to this region is required avoiding the potentially infected oral cavity; and while approaching the middle cervical segment in patients with a short neck or Klippel Feil anomaly and when the C3 vertebra is situated high in relation to the hyoid bone, the anterior retropharyngeal approach (ARPA) is the optimum surgical approach.,,,, In this study, key technical points and indications for ARPA are discussed.
Five patients with high cervical extradural compression underwent surgery using ARPA to the cervical spine between 1994 and 1999. Their clinical presentation is summarized in [Table I]. The mean age at presentation was 43.6 years and the average duration of symptoms, 27.2 months. Their pre- and postoperative clinical status was defined using Harsh's myelopathic grade. Plain radiographs of the cervical spine and magnetic resonance imaging (MRI) in sagittal and axial cuts were done in all cases. A computed tomographic scan with sagittal reconstruction images was also performed in three patients (cases 1, 2 and 5) to further delineate the bony pathology. The surgical procedures that were carried out utilizing the ARPA included excision of ossified posterior longitudinal ligament (n=2); excision of disc with osteophytes (n=2); and, excision of a vertebral body osteochondroma (n=1). Following the procedure, vertebral arthrodesis was achieved using an iliac graft in all the patients. Only one patient with vertebral body neoplasm required an additional anterior cervical plating procedure in order to stabilize the construct.
Patient position and incision [Figure. 1a] : The patient is placed supine on the operating table. Crutchfield cervical traction is placed to stabilise the neck during the procedure. The patient is positioned with a pillow under the shoulder, the head extended on a head ring and rotated 30o to the contralateral side. A transverse submandiblar incision is placed 2 cm inferior to the mandible, extending from slightly across the midline to the anterior border of the sternocleidomastoid., The marginal mandibular branch of the facial nerve runs forwards below the angle of the mandible under cover of the platysma and the skin incision 2 cm below and parallel to the inferior border of the mandible ensures its preservation.
Cervical dissection [Figure. 1b] : The superficial cervical fascia including the platysma is incised transversly in line with the skin incision and retracted, thus exposing the investing lamina of the deep cervical fascia enclosing in different fascial sheaths, the sternocleidomastoid muscle, the strap muscles, trachea, oesophagus and the recurrent laryngeal nerve. The investing lamina of the deep cervical fascia is opened and the retromandibular branches of the common facial vein ligated. The facial artery is retracted superolaterally towards the mandible. The exposed mandibular gland is elevated superolaterally, carefully preserving its duct in order to prevent a salivary fistula [Figure 1c]. The intermediate tendon of posterior belly of digastric muscle is held to the body and the greater cornu of the hyoid bone by a fibrous loop. This fibrous loop is incised mobilising the digastric muscle and retracting it superiorly. The stylohyoid muscle is also divided and retracted superiorly., This permits the exposure of the hypoglossal nerve, which is also carefully dissected free and retracted cranially, exposing the hyoglossus muscle and the greater cornu of the hyoid bone [Figure. 1d]. This procedure allows a medial retraction of the hyoid bone and hypopharynx.
Wide dissection of the fascial plane between the sternocleidomastoid and the carotid sheath laterally and the hypopharynx, trachea and oesophagus medially, permits exposure of the retropharyngeal space and the prevertebral fascia covering the longus colli muscles [Figure. 1e]. Care is taken not to injure or stretch the superior laryngeal nerve which courses deep to the internal carotid artery along the constrictor muscles of the pharynx. The retropharyngeal areolar tissue and the prevertebral fascia are opened exposing the anterior surface of the anterior arch of atlas and the C2 and C3 vertebrae [Figure. 1f].
Bony drilling : An orientation to the midline is gained by noting the attachment of the longus colli muscle on both sides as they converge towards the anterior tubercle of atlas as well as the anterior longitudinal ligament in the midline. The amount of rotation of the atlas may be gauged by palpating the anterior tubercle of the atlas. Using a monopolar cautery, the anterior surface of the vertebral bodies is exposed. The medial segment of the vertebral bodies is removed using a cutting burr till the inner cortical shell remains and this is further removed using diamond burr and Kerrison's punch. A wide midline gutter of 1.2 to 1.5 mm is made in the vertebral bodies leaving the lateral pillars intact., The posterior longitudinal ligament is excised exposing a bulging dura. During the drilling of the inner cortical bone, there may be severe bleeding from the epidural veins which is controlled by bipolar coagulation and surgicel. In case there has been a breech in the dura, it can be covered by a thin layer of fat and lumbar drainage instituted for three days along with acetazolamide administration.
Bony arthrodesis : A tricorticate iliac graft is positioned into the corpectomy defect after applying manual traction on the mandible to distract the vertebral bodies. Once the graft has snugly fitted into the gutter, the manual traction is released and the traction removed. In one of the patients, in whom the osteochondroma was involving the lateral part of the vertebral body, an anterior cervical plating was also performed [Figures. 2], 3). A bicorticate purchase was obtained on the vertebral bodies above and below the level of the corpectomy and the correct position confirmed by using an intraoperative image intensifier. One screw was also passed into the allograft. However, this did not traverse the posterior surface of the graft.
Postoperative management : The patients were weaned off the ventilatory support as soon as possible and were mobilised on a hard cervical collar. At follow up after one and a half and three months, their clinical status was evaluated again using the Harsh's functional myelopathic grade and lateral cervical radiographs were obtained to assess for the stability of the construct.
Three of the five operated patients had significant improvement in spasticity and power (Cases 1, 4, and 5). Case 2 had no preoperative myelopathy but significant pain in the nape of neck which completely resolved following stabilization. Case 3 with OPLL spanning several vertebral segments, in whom the significant extadural venous bleeding precluded total removal of the OPLL, the residual spasticity and unilateral deterioration in power by one grade persisted at follow up [Figure. 4]. The lateral radiograph of the cervical spine at follow up in all the five patients revealed that the construct was well placed and there was no lysthesis. The complications of the procedures included transient respiratory insufficiency requiring ventilatory support as well as neurological deterioration in two patients; and, pharyngeal fistula and donor graft site infection in one patient. There was no perioperative mortality. Though two patients with OPLL had dural breech during the surgery, there was no postoperative cerebrospinal fluid leak. None of the patients in the series developed hypoglossal nerve paresis.
A number of studies have established the usefulness of ARPA in providing a wide exposure from the basiocciput of clivus and anterior rim of foramen magnum to the rostral cervical spine upto C4.,,,, An additional caudal dissection in the fascial plane between the carotid sheath laterally and the trachea and oesophagus medially gives access to the entire cervical spine. According to the normal anatomy, the C1-2 disc space corresponds to the angle of mandible, the C2-3 disc space to the lower border of the mandible and the C3 body to the hyoid bone. The standard anterior approach to the subaxial spine allows an easy exposure of the anterior cervical spine from C3 to C7., However, in three patients in this series, the ARPA rather than the conventional anterior approach was used to treat prolapsed intervertebral disc at C3-4 level (n=2) and osteochondroma of the C3 vertebra (n=1). The indications for using ARPA in the two patients with C3-4 disc prolapse (Cases 4 and 5) were the presence of a short neck in one patient and a coexisting craniovertebral junction anomaly in the other. The preoperative lateral radiographs of the cervical spine in these cases had revealed the existence of the C3-4 disc space at a higher level than the hyoid bone and the lower border of the mandible. In the patient with C3 osteochondroma, the anterior cervical plating necessitated the complete exposure of C2 vertebral body and the passage of a bicortical screw through it. Thus approaching the C34 disc space in the former and the exposure and instrumentation of C2 vertebra in the latter using the conventional anterior approach would have been difficult due to the superomedial obliquity of the trajectory and would have required significant traction on the soft tissues.
Vender et al have summarised the advantages of ARPA in accessing anteriorly situated lesions from C1 to C3. Besides achieving a wide, bilateral exposure, the approach avoids the potential contamination of the oropharyngeal cavity and thus provides for a simultaneous arthrodesis and instrumentation during the primary surgical procedure. It also provides a safer environment for a simultaneous intradural procedure and management of a cerebrospinal fluid fistula.
Moreover, in case the occipito-atlantoaxial conFigureuration is not disturbed, the stabilisation procedure excludes the occipito-axial joint, thus preserving the vital lateral rotatory movements at the neck. Thus, the technique is specially favourable for dealing with ventrally situated lesions extending from C1 - C3, especially when long vertebral segments are involved as in OPLL, cervical spondylosis and bony tumours and especially when a simultaneous anterior vertebral arthrodesis and instrumentation is also required. However, the anterior decompression of the cervicomedullary junction restricted to the level of clivus and the anterior arch of atlas is not usually preferred using the present approach because the trajectory of the approach is superomedial and the head is also rotated towards the contralateral side causing a simultaneous rotation of the arch of atlas. This makes it difficult for the surgeon to orient himself regarding midline of the cervical spine as a direct anterior visualisation of the vertebral bodies at this level is not possible. In such patients the transoral approach,,, can be utilised which has the advantage of being a straight midline approach through an avascular median raphe. This also ensures direct anterior bony exposure of upper cervical segment through a familiar anatomy. Moreover, it allows foramen magnum decompression in neck extension which is especially useful while dealing with atlantoaxial dislocations. However, the surgery is performed at the depth of a narrow field with vital cervicomedullary centers underneath and therefore carries the inherent risk of neurological deterioration. Passage through a potentially infected oral cavity may produce infection and precludes a simultaneous intradural access or a stabilisation procedure during the primary surgery. This approach does not provide a good caudal access to the cervical spine without combining it with a mandibular osteotomy and tongue splitting, the lateral exposure also being limited to 3-4 cm, due to the emergence of the hypoglossal nerves, the vertebral artery and the eustachian tube laterally. Wide excision of the osteoligamentous components may produce instability which requires a separate procedure for stabilisation. The disadvantages of the transoral route can be avoided utilising the ARPA especially when access to the middle and lower spinal segments is simultaneously being sought along with access to the upper cervical segment and also when an anterior bony arthrodesis is being considered.
Two patients out of five developed respiratory insufficiency requiring ventilatory support. The
patients with a high cervical cord compression show the syndrome of afferent respiratory dysfunction. A number of cumulative factors like laryngeal oedema due to retraction, pent up larygobronchial secretions, compromise of the diaphragmatic function, weakness of accessory respiratory muscles and increased thoraco-abdominal muscle tone contribute to this complication. Both patients were vulnerable to sleep induced apnoea and required assisted ventilation. However, the respiratory functions improved with time and both patients could be weaned off the ventilator. Transient neurological deterioration also occurred in two patients, however, it was more sustained in the second case. In the latter patient, there was brisk extradural bleeding during the OPLL removal, and a part of the compressing segment of the OPLL could not be removed. This perhaps was responsible for the sustained neurological deterioration at follow up. During the drilling of the vertebrae, application of a lateral rather than a downward pressure and leaving a thin posterior cortical surface of bone which is removed using Kerrison's punches, is recommended to prevent potential neuraxial injury. It is also important for the surgeon to gain orientation to the midline. The rotation of head away from the midline, which also rotates the anterior arch of atlas, can be assessed by palpating the mental protruberance of the mandible. Maintaining this orientation throughout the anterior decompression of the spinal cord ensures that the drilling is carried out far enough laterally to permit a wide decompression of the cord and its expansion into the gutter created but not so far laterally so as to endanger the vertebral arteries. A simultaneous stabilisation during the primary procedure avoided the danger of neurological deterioration due to instability.
The pharyngeal fistula occurred in one patinets, due to retractor injury to the thin layer of superior constrictor muscle that separates the hypopharynx from the area of dissection. In such cases, if the injury is detected during surgery, then the fistula can be closed in two layers using absorbable sutures. In our patient, the placement of nasogastric tube for seven days, restricting the oral feeds and providing a broad spectrum antibiotic coverage sufficed in overcoming the complication.
Transient hoarseness and dysphagia following anterior cervical spine surgery is attributable to swelling in the soft tissues of pharynx and larynx due to retraction. The hoarseness may also be due to neuropraxia of the superior or recurrent laryngeal nerve. Compression of the anterior branch of the recurrent laryngeal nerve between the thyroid lamina and the endotracheal cuff as the branch passes under the mucosa of the larynx to the lateral cricoarytenoid and thyroarytenoid muscles may also be a contributory factor. A gentle dissection of adequate length through the fascia situated between the carotid sheath laterally and the hypopharynx, larynx and trachea medially; avoiding unduly vigorous retraction; placement the Cloward's retractor blades under the edge of the laterally dissected longus colli muscles; frequent releasing of the tension on the retractors especially when they are not actually required such as when the graft is being harvested, avoids the hoarseness and dysphagia.
The dural breech, that occurred in the two patients, whose OPLL was adherent to the outer layer of the dura, was covered with a fat graft. Acetazolamide administration and lumbar drainage were instituted to decrease the cerebrospinal fluid pressure., Fortunately, there was no leak following removal of sutures. The other complications that may occur while utilising this approach include hypoglossal nerve paresis due to its mobilisation; salivary fistula during the submandibular gland mobilisation; traction injury to the facial nerve in the viscinity of the stylomastoid foramen due to retraction at the base of origin of stylohyoid or posterior belly of digastric muscle, carotid artery occlusion due to prolonged retraction in association with atherosclerotic disease or carotid artery injury especially due to avulsion of one of its tethering branches; vertebral artery injury during the removal of lateral osteophytes or while dissecting the longus colli laterally using the cutting cautery especially when orientation to the midline is lost, injury to the sympathetic chain deep to the longus colli muscle resulting in Horner's syndrome, and, graft dislodgement and donor site complications.
In the cervical spine, median corpectomy only partially compromises the anterior spinal support segment while the lateral segment comprising the pedicle and facet joints and the posterior segments are intact. In our series, after the corpectomy or Cloward's procedure, this theoretical instability was taken care of by interposition of autogenous bone graft harvested from the iliac crest. In four patients, the bone graft was snugly fitted into the gutter created in the center of the vertebral bodies by distracting the spine using manual traction. We did not perform any instrumentation in these patients in order to facilitate
postoperative magnetic resonance imaging. Though an early mobilisation was achieved in all these patients, with the neck movements only restricted by a hard cervical collar and not a Minerva jacket or a halo brace, a good bony construct was noted at follow up radiological evaluation. In the patient with osteochondroma, a wider drilling of the lateral vertebral body pillars prompted an internal fixation procedure to stabilise the bone graft. An AO plate system was used and a bicortical purchase through the vertebrae above and below the level of the pathology was ensured using intraoperative biplanar fluoroscopy.,
The ARPA is an exteremly useful and safe approach in accessing anteriorly situated lesions at C1-3 especially in patients with a short neck, Klippel Feil anomaly or those in whom the C2-3 and C3-4 disc spaces are situated higher in relation to the hyoid bone and the angle of mandible. It achieves a wide, bilateral exposure, avoids the potential contamination of the oropharyngeal cavity and provides for a simultaneous arthrodesis and instrumentation during the primary surgical procedure. For accessing long cervical vertebral segments, it can be combined with the conventional anterior approach. However, for strictly midline lesions restricted to the craniocervical junction, the superomedial trajectory of the approach renders it difficult for the surgeon to maintain his orientation of the midline during the bony drilling.