Pathologies involving the craniocervical junction require comprehensive surgical management to relieve the bulbomedullary compression and ensure spinal stability. Many factors need to be considered when opting for anterior, posterior or combined approaches, including the nature of the lesion, its natural history, and prognosis. This chapter will cover the fundamental aspects of neuroradiologic workup, intraoperative neuronavigation, and neurophysiologic monitoring needed to ensure a safe surgical intervention while reducing the risk of perioperative complications. Also, aspects pertaining to anesthesiological management and postoperative care, from immobilization to chemo-/proton-beam/radiotherapy, will be discussed in detail.
Keywordscraniocervical junction, bulbomedullary lesions, intraoperative neuronavigation, spine stability, adjuvant radiotherapy
The primary treatment goals for pathologies involving the craniocervical junction are the relief of bulbomedullary compression and the elimination of instability, if present. The choice of anterior or posterior approaches depends on the nature of the lesion, its natural history, and prognosis.
A complete neuroradiologic workup, the use of neuronavigation (C-arm, O-arm, intraoperative computed tomography/magnetic resonance imaging), and neurophysiologic monitoring (somatosensory and motor evoked potentials) help reduce the risk of perioperative complications.
Vertebral artery mobilization and occipital condyle resection may be needed depending on the extent and location of craniocervical junction tumors; in case of significant condylar resection, occipitocervical fixation is warranted.
Although it is not ideal, the C2 ganglion can be sacrificed with minimal postoperative comorbidities, and in most cases, patients are asymptomatic from iatrogenic damage of the vertebral artery.
Postoperatively, Halo immobilization or chemo-/proton-beam/radiotherapy can be considered as adjuvant treatments, depending on the nature of the lesion.
Like a cardan joint, the craniocervical junction (CCJ) allows simultaneous independent spatial movements around three axes; its primary role is in fact to ensure the maximal mobility of the head for visual and auditory exploration of space. These functional characteristics explain the complexity and fragility of this anatomic region. Over the years, many anterior, anterolateral, and posterior approaches to the CCJ (such as: transoral, transfacial, transmandibular, endoscopic transnasal, midline, or lateral or far lateral occipitocervical decompression coupled with instrumented fusion achievable by many techniques) have been developed to address the bulbomedullary compression caused by several degenerative, inflammatory, traumatic, congenital, and neoplastic spine pathologies ( Fig. 50.1 ). These include but are not limited to: (1) chronic inflammation of the CCJ osteoligament complex, mostly related to rheumatoid arthritis and metabolic disorders; (2) traumatic C1–C2 dislocations resulting in basilar invagination as well as unstable atlas and odontoid fractures; (3) congenital malformations causing instability and/or stenosis at the level of the CCJ, like those resulting from collagenopathies, osteogenesis imperfecta, Down’s syndrome, and achondroplasia; and, (4) neoplastic (i.e., primary and secondary spinal tumors) and paraneoplastic (i.e., Paget’s disease) lesions, usually affecting the body and dens of C2.
The CCJ represents a transitional zone with a complex balance of different elements: osseous structures articulated with synovial joints, intrinsic ligaments, membranes, and muscles. From a biomechanical perspective, the CCJ can be thought of as a central pillar surrounded by two ringed structures: The first consists of clivus, anterior atlanto-occipital membrane (AAOM), odontoid process, and the vertebral body of C2, whereas the second includes the foramen magnum (FM) with the occipital condyles, the posterior atlanto-occipital membrane (PAOM), and the ring of C1 with its lateral masses and arches. Altogether those elements respond to seemingly opposed necessities: being at the same time loose enough to allow a great variety of movements yet strong enough to preserve the spinal cord and vertebral arteries. The anatomic structures more at risk of injury during surgical approaches to the CCJ are described below.
Brainstem, Spinal Cord, Cranial and Spinal Nerves
Among the structures passing behind the alar ligament that divides the posterior compartment of the FM from its anterior, osseoligamentous one are the lower end of the medulla oblongata (MO) with anterior and posterior spinal arteries, the spinal root of the accessory (XI) nerve and, occasionally, the lower aspect of the cerebellar tonsils. Pathologies causing bulbomedullary compression may result in concomitant involvement of the nuclei and ganglia of several cranial nerves arising from the MO: nucleus ambiguus of glossopharyngeal (IX) and vagus (X) nerves; dorsal nucleus, solitary nucleus, and inferior ganglion of X nerve; spinal accessory nucleus of IX nerve; and hypoglossal nucleus of the hypoglossal nerve (XII). Pathologies eroding or infiltrating the occipital condyle and jugular foramen (JF) may result in a compression, stretching, or infiltration of IX nerve with its tympanic branch (for involvement of the pars nervosa of JF), X nerve with its auricular branch and XI nerve (for involvement of pars vascularis of JF). Similarly, some upper cervical nerves may be affected by pathologies affecting the CCJ and extending caudally; those spinal nerves are: the suboccipital nerve (C1 root), the greater occipital nerve (C2 root) and, rarely, the small occipital nerve (C3 root). Overall, the neurologic symptoms resulting from involvement of the neural elements cited above can range from dysphagia, dysarthria, and dysgeusia to neck pain and occipital neuralgia. Full neurologic examination with testing of gag reflex, light touch, and pinprick sensation in the territories of the upper spinal nerves is therefore recommended to identify subclinical signs.
The vertebral artery (VA) provides segmental vertebral and spinal column blood supply; cranially, it continues with the basilar artery (BA), providing supply to the posterior fossa and the occipital lobes. Of the four segments of the VA, the two pertinent to the CCJ are the V3 and V4. The V3 segment emerges from the transverse process of C2, crosses the C2 root, and sweeps laterally to pass through the transverse foramen of C1 (vertical portion of V3). From here it passes around the posterior border of the lateral mass of C1, keeping the C1 root on its medial side; it then lies in the groove on the upper surface of the posterior arch of C1 and enters the vertebral canal by passing beneath the PAOM, lateral to the cervicomedullary junction (horizontal portion of VA). Finally, passing superomedially, it pierces the dura and the arachnoid to continue intracranially as the V4 segment of VA, which at the level of the FM is surrounded by a sympathetic plexus. The V4 segment inclines medially in front of the MO and is located between the XII nerve and the anterior root of the C1 nerve; at the lower border of the pons, it unites with its contralateral VA to form the BA. In up to 18.8% of cases, a bony bridge called the arcuate foramen covers the VA groove on C1. Asymmetry of VA may be due to hypoplasia or, more commonly, the presence of a dominant side: A statistically significant left dominance was found in ultrasonography and angiographic investigation testing several anatomic and functional parameters such as diameter, peak systolic velocity, end-diastolic velocity, time-averaged mean velocity, resistance index, and flow volume. A strong correlation exists between the diameters of the transverse foramina and the blood flow of VA. Anatomic variations of the V3 segment of VA include: fenestration, aberrant VA, and origin of posterior internal cerebral artery (PICA) at C2 or C1. Damage to the VA is a concrete risk whenever performing an atlantoaxial fixation with Magerl technique, especially if the pars of C2 is narrow secondary to prominent looping of the VA into the pars. The consequences of VA injury can be potentially catastrophic, leading to thrombosis, embolism, and cerebrovascular events, or causing iatrogenic pseudoaneurysm formation; usually, though, a unilateral injury has limited impact on the postoperative course, and most of the patients from the largest series are described as asymptomatic from unilateral arterial injury.
Cervical Venous Plexus
Surgical techniques requiring careful exposure of the C1 lateral mass (e.g., C1–C2 screw-rod fixation with Goel or Harms techniques) have the advantage of reducing the risk of damage to the VA, but their complexity is increased by the venous plexus surrounding the C2 ganglion. This venous plexus is part of an extensive sinusoidal network of posterior veins associated with the neural arches communicating with segmental veins forming the deep cervical vein complex. Of note, in correspondence to the C2 ganglion, this venous plexus may be quite extensive and further engorged due to the prone patient position required for these procedures.
Anatomic variations of VA course (fenestrated VA, aberrant VA, origin of PICA at C2 or C1)
Thin squamous part of the occipital bone, small C1 lateral masses, small pedicles of C2/C3
Poor-prognostic preoperative factors, such as: smoking habit, weight loss, osteopenia, prolonged steroid treatment, neurologic deficits, Ranawat Class IIIB, metastatic disease
Risk of poor wound healing: anticipated blood loss exceeding 1000 mL, prolonged postoperative intubation/nasogastric feeding tube, need for adjuvant treatments (e.g., radiation therapy)
Re-do of surgery for recurrence of disease (e.g., malignancies) or postoperative instability
Prevention of complications starts with a careful preoperative workup. Regardless of the pathology and type of approach to the CCJ, every patient should undergo a magnetic resonance imaging study of the brain and cervical spine, coupled with a fine-cut computed tomography (CT) study of the CCJ and cervical spine. Appropriate imaging of the CCJ with CT angiography (CTA) or digital selective angiography (DSA) has to be considered for a careful study of the VA and its possible anatomic variations. The use of an intraoperative neuronavigation system and micro-Doppler ultrasonography can be advisable, depending on the pathology and the type of approach; intraoperative neurophysiologic monitoring with recording of somatosensory- and motor-evoked potentials is routinely recommended, with no exceptions. Patients with CCJ pathologies should always receive fiber-optic intubation; anterior approaches to the CCJ can require either nasotracheal or orotracheal intubation, depending on the use of a transoral or transnasal endoscopic approach. In both cases, however, a triple-antibiotic prophylaxis covering for gram-positive and gram-negative cocci should be considered to reduce the risk of contamination, and a dose of steroids (dexamethasone 4 mg) should be administered preoperatively to prevent edema or swelling of the mucosae. Patient positioning depends on the nature of the pathology addressed, the operative approach, and the surgeon’s preference: transnasal endoscopic approaches are generally performed with the patient in supine, slight anti-Trendelenburg position (20 degrees); for lateral and far lateral approaches to the CCJ, options include prone, park bench, and sitting position; for occipitocervical fusion, our preference is to use the Jackson table with the head fixed in a Mayfield three-pins head holder.