Basilar invagination and basilar impression both refer to the displacement of the odontoid process into the foramen magnum, although the former is congenital and the latter is due to secondary etiology.1 Many etiologies for basilar impression exist, including trauma, Paget's disease of the bone, osteogenesis imperfecta, rickets, and rheumatoid pannus.2 To our knowledge there have been no reports of basilar impression caused by radiation fibrosis of the odontoid process. We present this case with the subsequent novel indication for an endonasal transclival odontoidectomy.
A 66-year-old female with a history of advanced tonsillar carcinoma treated with primary radiation therapy 6 years prior presented with neck pain and falls. She was significantly deconditioned, wheel-chair bound, with progressive wasting, fatigue, cervical instability, and pain. She also exhibited significant trismus (1 cm). Computed tomography (CT) imaging revealed basilar impression with severe narrowing of the spinal canal to 6 mm at the level of the foramen magnum along with brainstem compression (Fig. 1A,B). Given her significant trismus, a transoral approach to the odontoid was not a viable option without a mandibulotomy. The nasopalatine line showed that transnasal access to the odontoid process was feasible.3 We provide a detailed description and video of the surgical approach (Video 1).
The anesthesia team understood the potential neck instability issues with the patient. In light of the patient's significant trismus and history of head and neck irradiation, awake tracheostomy was first performed to control the airway. We also anticipated postoperative cervical stabilization with Halo device and subsequent occipitocervical fusion.
Somatosensory-evoked potential monitoring was placed, and baseline potentials were obtained. This was done to monitor brainstem function during positioning. The head was placed in a Mayfield skull clamp in a neutral position. The patient's images were loaded into the stereotactic CT guidance system and registered to the patient. Image guidance was used to identify the level of approach to the arch of C1 and body of C2. It was also used to confirm lateral positions of the internal carotid artery and vertebral arteries. Given the lateral position of the vital structures, a Doppler was not utilized.
Afrin-soaked pledgets were placed in bilateral nasal cavities for decongestion. The patient was draped in normal fashion. The Afrin-soaked pledgets were removed and 1% lidocaine with 1:100,000 epinephrine was used for local anesthesia of the septum and attachment of the middle turbinate on the lateral nasal wall bilaterally. A Freer was used to slightly outfracture the bilateral inferior turbinates. The Freer was also used to very gently lateralize the bilateral middle turbinates; these were not resected. A 0° Hopkins rod was used for visualization.
First, inferior posterior septectomy was performed, sparing the posterior nasoseptal pedicles bilaterally. This was done with an extended guarded needle tip Bovie bent to 45° at a coagulation level of 25. The bony septum at the level of the nasomaxillary spine was removed with use of an extended guarded 4-mm coarse diamond bur drill. This allowed for adequate exposure and use of bilateral instrumentation. Sphenoidotomies were not performed as we believe these were not necessary for visualization of the more inferiorly located odontoid process.
Suction Bovie cautery set to 25 was then used to make a vertical opening in the nasopharyngeal mucosa from the level of the clivus down to the bottom of C1. Eustachian tubes, laterally, were not violated. The midline fascia of the paraspinal musculature was divided along the raphe with the suction bovie, and the musculature was lateralized. Image guidance confirmed the location of the clivus and arch of C1. There was a significant amount of fibrous tissue removed with kerrisons, curettes, and suction bovie cautery to expose the clivus and arch of C1 (Fig. 2).
An extended guarded 4-mm coarse diamond bur was then used to remove the inferior clival bone and anterior portion of the C1 arch. Care was taken to protect the lateral vertebral and carotid arteries by not allowing transfer of heat via the Bovie laterally. Once the C1 arch was removed, a Cottle was used to identify the lateral and most superior aspects of the odontoid. A diamond bur was then used to core out the central portion of the odontoid. The remaining cortical shell was removed in a piecemeal fashion using various instruments including Cottle, kerrisons, curettes, and microinstruments. After piecemeal removal, the remaining superior portion tethered to the dura was carefully drilled down and removed. After removal of the odontoid, dynamic pulsations and adequate decompression was confirmed and the dura was noted to be intact without evidence of cerebrospinal fluid leak. A Lumar drain was not indicated.
Nasopharyngeal mucosa and paraspinal musculature were not closed. Tisseel (Baxter Healthcare Corp., Deerfield, IL) and FloSeal (Baxter International Inc., Deerfield, IL) were placed in the defect. Somatosensory-evoked potential monitoring continued to retrieve potentials similar to baseline.
Postoperative instructions included utilization of isotonic saline rinses twice to four times daily. The patient ultimately underwent posterior occipitocervical fusion.
Postoperative imaging showed excellent resection of the odontoid process and decompression of the brain stem (Fig. 1C,D). Pathology showed fibrocartilagenous and atrophic processes of bone, with no recurrence of squamous cell carcinoma, active infection, or osteomyelitis. The patient had no evidence of cerebrospinal fluid leak, spinal cord injury, or large vessel injury. Initial bilateral upper strength weakness significantly improved with physical therapy. She was placed in a skilled nursing facility because of preoperative wheelchair dependency and severe extremity weakness. She was decannulated 3 weeks postoperatively. By 5 months postoperatively, the patient moved out of her skilled nursing facility, had good strength in all four extremities, was ambulating well, was gaining weight, and had a self-reported significantly improved quality of life.
Treatment of locally advanced head and neck squamous cell cancer may cause complications such as xerostomia, damage to dentition and small vessels, viral and fungal infection, trismus, articulatory sequelae, dysphagia, and radiation fibrosis syndrome.4–6 Radiation fibrosis is an irreversible process that may cause acute or late toxicity after induction of radiation therapy. Initial phases are marked by chronic nonspecific inflammation, causing destruction of the endothelial cell barrier and thus fibroblastic activation. Later stages demonstrate remodeling of the extracellular matrix with deposition of fibrin and atrophy of normal tissue.7 All tissues of the head and neck may be affected.8
Our patient's differential diagnosis included recurrence of squamous cell carcinoma, radiation-induced neoplasm, osteoradionecrosis, and osteomyelitis. None of these diagnoses were supported by imaging. Pathology reports confirmed our initial diagnosis of radiation fibrosis. Radiation fibrosis of the odontoid process poses unique challenges for therapy, but the otolaryngologist must be prepared for such a possibility, especially if the transoral corridor is not available for use.
Although the transoral route has traditionally been the gold standard corridor for surgical access to the craniocervical junction, endonasal approaches are gaining popularity. The endonasal approach was first described through anatomical studies by Alfieri et al. in 2001.9 Since that time, few case series have been published using this approach.10–15 The advantages of the endonasal approach over the transoral route are tremendous. There is no need for splitting of the hard and soft palate, thus dramatically decreasing the rate of velopharyngeal incompetence and dysphagia. Postoperative tongue edema with associated hypernasal speech and ischemic necrosis are avoided. Tracheostomy and gastrostomy tube feeding are less likely to be required.16 In this particular case, airway management was a significant issue, and a tracheotomy was performed but removed by postoperative day 10. Disadvantages include limited access to lesions rostral to C2 and a possible higher learning curve. However, the endonasal approach does allow for a chance of decreased morbidity, as in this case where sphenoidotomies were not performed and a nasopharyngeal mucosal flap was not created. This actually reduced the operative time and nasal morbidity for this patient.
Basilar impression and brainstem compression can be a rare complication of radiation fibrosis syndrome. Endonasal odontoidectomy is an effective approach for anterior decompression of the craniocervical junction, and may especially be valuable in cases where a transoral approach is precluded. The head and neck surgeon should be facile in both approaches to allow for surgery in a wide variety of circumstances.
The authors would like to thank Nicolette DeGroot for her illustrations.