14.1 Introduction

The craniovertebral junction (CVJ) is composed of both bony and neurovascular and ligamentous structures (▶ Fig. 14.1). The bony anatomy includes the clivus and dens ventrally, the condyles laterally, and the opisthion of the suboccipital bone and arch of C1 posteriorly. ¹ The condyles articulate with C1 to create the atlantoaxial complex. ¹ Abnormalities, many of them developmental, are common in this neuroanatomical region, particularly in the pediatric population. Down’s syndrome, Chiari’s malformation (CM), neoplasm, osteogenesis imperfecta, juvenile rheumatoid arthritis (JRA; Still’s disease), achondroplasia, cleidocranial dysostosis, Klippel–Feil triad, ² and Morquio’s syndrome are often associated with CVJ abnormalities. ³

Basilar invagination and cranial settling with resultant ventral brainstem compression are common indications for an odontoidectomy in pediatric patients. Basilar invagination occurs secondary to an upward migration of the odontoid process. Several factors define the severity and/or complexity of basilar invagination or brainstem compression: degree of upward migration of the odontoid process, degree of retroflexion of the odontoid process, volume of ligamentous pannus associated with the articulation over the dens, coincidence of atlantoaxial instability, ⁴ volume of the posterior fossa, surrounding soft tissue (normal or pathological), and associated pathological disorders.

CM is commonly associated with varying degrees of cerebellar herniation through the foramen magnum. CM has classically been defined as existing on a spectrum containing four types. Type I is the most common type, and is associated with the most favorable prognosis. It is by far the most commonly observed type in children, but is often first diagnosed only in adulthood. Characteristic features include tonsillar descent below the level of the foramen magnum, resulting in the possible disruption of normal cerebrospinal fluid (CSF) flow around and through the foramen magnum. Syringomyelia is present in 30% to 70% of these cases. Type II is more severe and is associated with myelomeningocele. Type III is usually associated with encephalomeningocele and is not compatible with life. Type IV is characterized by hypoplasia of cerebellar tissue.

Recently, the term “CM 1.5” has been used to identify a subgroup of patients with brainstem herniation (defined as obex below the level of the foramen magnum) in addition to tonsillar herniation. Data suggest patients with CM 1.5 frequently present with bulbar signs and symptoms, have distortion of the brainstem on sagittal MRI, and fail standard posterior decompression significantly more frequently than patients with CM without these features. ⁵ CM 1.5 patients are also at increased risk for requiring an occipitocervical fusion, following a standard decompressive procedure. ⁶ The combination of disruption of normal stabilizing forces as well as the common comorbid presence of connective tissue disorders is thought to underlie this morbidity of decompression.

Down’s syndrome is also associated with ligamentous laxity (15%–20%) commonly resulting in atlantoaxial subluxation. ⁷ This finding can result in cervicomedullary compromise and myelopathic features. Surgical stabilization as well as odontoidectomy might be indicated in some cases.

JRA is the most common rheumatologic disease in children, and is one of the most common chronic disease conditions in childhood. It is defined as arthritis beginning before the age of 16 years, but the frequency is highest in children younger than 3 years. ⁸ The formation of a rheumatoid pannus at the odontoid–C1 articulation can cause symptomatic ventral compression of the brainstem in some children.

Tumors of the CVJ could be primary or secondary and either intradural or extradural. Congenital lesions like neurenteric cysts can also be encountered in this anatomical region. Other lesions include craniopharyngiomas, eosinophilic granulomas, neurofibromas, chordomas, chondrosarcomas, osteoblastomas, osteoid osteomas, and giant cell tumors. The clinical features range from headaches and neck pain to torticollis ⁴ and severe myelopathy. Other symptoms like drop attacks, migraines, and collapse could be due to vertebrobasilar insufficiency syndrome, in which case an angiographic study should be recommended as part of the preoperative evaluation.

14.2 Management Options: Medical, Surgical and Adjuvant

Medical, surgical, and adjuvant treatment options will vary by the specific pathology at the CVJ. Tumors in this region, although usually benign, are often chemo-/radioresistant, and surgical excision is often the treatment of choice. Several surgical approaches to the CVJ can be considered, including transfacial, ^{9 ,​ 10} transoral, lateral extrapharyngeal, far lateral, transcondylar, and expanded endonasal endoscopic ¹¹ (▶ Fig. 14.2).

The main indication for an odontoidectomy is radiologic and symptomatic ventral brainstem compression. Over the years, different radiographic criteria have been used to select patients who need odontoidectomies/ventral brainstem decompression. The basilar lines—Chamberlain’s line, ^{2 ,​ 12} McGregor’s line, ^{2 ,​ 13} Wackenheim’s line, ¹⁴ McRae’s line, ^{2 ,​ 15} bimastoid line, etc. ¹⁶ —as well as other radiographic criteria ¹⁷ proposed by Ranawat et al, ¹⁸ Redlund-Johnell and Pettersson, ¹⁹ and Clark et al ²⁰ have all been used for the assessment of basilar invagination.

Goel et al ²¹ classified basilar invagination, diagnosed using Chamberlain’s line, into two groups based on their study of 190 surgically treated patients. Eighty-eight patients who had basilar invagination but no associated CM were assigned to group I; the remainder of the patients, who had both basilar invagination and CM, were assigned to group II. They highlighted that transoral decompression was the most suitable procedure for group I patients, while foramen magnum decompression was advised for group II patients.

Contrary to these data, Grabb et al ⁶ showed that in pediatric patients with Chiari I malformation as well as ventral brainstem compression from basilar invagination, a posterior decompressive procedure alone may not provide symptomatic relief and, in some cases, may lead to worsening of symptoms. They developed a novel method using sagittal MRI that measured objectively the encroachment by the odontoid and its investing tissues into the foramen magnum. They demonstrated that a value of 9 mm or greater was associated with a high risk for ventral brainstem compression, and some of these patients might warrant traction or transoral odontoidectomy before undergoing posterior fossa decompression.

Bollo et al ²² showed that patients with basilar invagination, CM 1.5, and craniocervical angulation (clivoaxial angle [CXA]) less than 125° are at increased risk of requiring an occipitocervical fusion procedure, either as an adjunct to initial surgical decompression or in a delayed fashion.

14.3 Endoscopic Endonasal Surgery

The transoral approach was the historical gold standard for ventral decompression at the CVJ by means of an odontoidectomy (▶ Fig. 14.3). Alfieri et al ²³ developed the endoscopic endonasal approach (EEA) to the CVJ and odontoid process using cadaveric dissection in 2002. ²³ Later, Kassam et al provided a description of EEA for resection of odontoid process and rheumatoid pannus in a patient with symptomatic cervicomedullary compression. ²⁴ Since then, the EEA is now advocated by many surgeons as an alternative, as it avoids breaching the oropharynx and is an effective minimal-access technique for decompression of the cervicomedullary junction. ^{25 ,​ 26 ,​ 27}

When compared with the transoral approach, ^{28 ,​ 29} endoscopic endonasal access presents four potential advantages: (1) excellent prevertebral exposure and lateral visualization in patients with small oral cavities, (2) a surgical corridor located above the hard palate that allows easy decompression of rostral pathological entities, (3) avoidance of the oral trauma and edema that follow oral retractor placement, and (4) avoidance of splitting the soft or hard palate and preservation of palatal function. ^{27 ,​ 30}

The endonasal approach can provide excellent access to the clivus, C1, and C2 (odontoid) without the need for external incisions, Le Fort osteotomy, mandibular split, or a circumglossal approach usually required for patients with a small oral cavity, trismus, or macroglossia. The incision used for the endonasal approach is more rostral in the nasopharynx (ideally at or above the level of the soft palate) than the posterior pharyngeal incision used for the traditional transoral approach. This spares the posterior pharynx musculature and mucosa, which may lead to a reduction in wound-healing complications and velopharyngeal incompetence. ¹¹ There are several studies reporting that compared to the transoral approach, the endonasal approach to the CVJ leads to more rapid extubation and earlier time to feeding. ^{26 ,​ 27 ,​ 30}

Through radiographic and cadaveric morphometric analysis, Singh et al showed that the odontoid peg (comprising roughly two-thirds of C2 vertebral body in sagittal plane) can be endonasally accessed more than 90% of the time using a 0- or 30-degree endoscope, without splitting the hard or soft palate. ^{31 ,​ 32} Similarly, other authors have also evaluated the inferior anatomic extent of odontoidectomy through an endonasal approach, which might be helpful in preoperative surgical planning. ^{33 ,​ 34}

In pediatric patients, characteristic anatomical features like small nostrils, presence of adenoids, and absent or limited pneumatization of sinuses pose a different type of challenge to endoscopic surgeons, as discussed in Chapters 1 and 2. According to our experience, while the patient’s age as well as size is not a significant limitation to the EEA, ^{35 ,​ 36} a wider intercarotid distance (ICD) and shorter dens–nare distance predicts better outcomes and fewer complications. ^{37 ,​ 38}

In our series of six pediatric patients who underwent endonasal odontoidectomies for CVJ compression, five of six patients had improvement in their modified Rankin’s scale (mRS) scores on follow-up (▶ Table 14.1). ³⁹

14.3.1 Case Example

An 11-year-old with Ehlers–Danlos syndrome had cervical instability and brainstem compression from basilar invagination and a retroflexed odontoid. He also had a Chiari 1 malformation (▶ Fig. 14.4; ▶ Fig. 14.5a). His symptoms consisted of headaches and loss of feeling in his arms, hands, legs, and feet. He also had choking and gagging spells and poor balance.

He underwent a Chiari decompression and occipitocervical fusion, followed by endoscopic endonasal resection of the odontoid.

He was positioned supine and his head was pinned in three-point fixation in a radiolucent Mayfield head holder. Neuronavigation was set up using the intraoperative CT scanner. In the absence of an intraoperative CT scanner, registration coordinates may also be acquired using a preloaded MRI and/or CT scan of the patient. Neuromonitoring was set up, and motor and somatosensory evoked potentials were monitored throughout the surgery.

A posterior septectomy is performed and the nasopharynx approached using a binostril approach. In pediatric patients, large adenoids (Ad) can occasionally obscure the choana (▶ Fig. 14.6).

The adenoids are resected for improved visualization and access to the posterior nasopharynx. A vertical incision is made in the posterior pharyngeal musculature using Bovie electrocautery. The suction is used for dynamic retraction of the pharyngeal musculature and the anterior arch of the C1 ring is exposed. The incision can be extended cephalad to expose the inferior portion of the clivus as well. In some cases of severe invagination, the inferior portion of the clivus might also need to be drilled and removed (▶ Fig. 14.7).

The anterior arch of C1 is drilled off to expose the odontoid peg. The Eustachian tubes mark the lateral borders of the dissection (▶ Fig. 14.8).

The odontoid peg is hollowed out with a high-speed drill and then detached at the base. The remainder of the odontoid shell must be detached from the apical and alar ligaments superiorly and the cruciate ligament posteriorly for complete removal. Curettes and Kerrison rongeurs are helpful in dissecting the ligaments off the odontoid shell to remove it piecemeal (▶ Fig. 14.9).

Once the odontoid peg and cruciate ligament are removed, the glistening dura can be seen. Care must be taken to not cause a CSF leak while detaching the odontoid and cruciate ligament (along with the pannus) from the underlying dura (▶ Fig. 14.10). However, if a CSF leak is encountered, it can be repaired with autologous fat onlay and Tisseel fibrin glue, and held in place by suturing the overlying nasopharyngeal fascia utilizing chromic sutures.

The intraoperative CT scanner is now used to perform a second scan while acquiring new registration coordinates. This helps us access the adequacy of the bony decompression at the CVJ. If there is residual odontoid seen, further decompression is pursued using the newly acquired registration coordinates to localize the residual fragment. ⁴⁰

When the odontoidectomy is complete, the posterior pharyngeal musculature is approximated together using absorbable stitches. Some Floseal (Baxter, Deerfield, IL) might be placed in the cavity to eliminate some of the dead space (▶ Fig. 14.11).

All of our endoscopic odontoid resection patients who did not have occipitocervical fusion performed under the same anesthesia are extubated in the operating room. Patients who received combined fusion and odontoid decompression are electively extubated on the morning of postoperative day 1 to allow airway edema to subside after 8 to 10 hours of surgery, much of it in the prone position for the fusion portion of the case. Diet is resumed shortly thereafter.

Intraoperative CT has proven useful for delineating the adequacy of surgical decompression at the cervicomedullary junction by identifying residual bony fragments. ^{39 ,​ 40 ,​ 41} Whether these small residual fragments are clinically significant is unknown, but complete resection of the odontoid is more likely to relieve symptoms than a partial resection. Ongoing clinical assessments will try to elucidate these questions further.

Right-handed surgeons operating predominantly through the right nostril should pay special attention to the contralateral (left) side of the resection, where there is often a tendency toward residual pathology. ^{27 ,​ 40} We hypothesize that this is because it is easier to retract the posterior pharyngeal musculature (using a suction) and drill the C1 ring and odontoid on the right than on the left where there is continuous overhang of the pharyngeal musculature.

Special attention should be paid to patients who are undergoing occipitocervical stabilization and fusion at the same time as the endonasal odontoidectomy. These patients should be fused in their neutral anatomic alignment presurgery. If they are fused in a flexed or posteriorly translated position, they can develop significant problems with swallowing postoperatively. The posterior pharyngeal edema postsurgery, in conjunction with the flexed and/or posteriorly translated position at the CVJ, can lead to airway compromise in severe cases (▶ Fig. 14.12).

Related posts:

12 Meningoencephaloceles 13 Sellar Arachnoid Cysts 16 Craniopharyngioma 23 Chordoma 25 Malignant Skull Base Tumors 26 Subperiosteal Orbital Abscess

Stay updated, free articles. Join our Telegram channel

Join