Origin and Occurrence
The craniovertebral junction, along with the clivus, is a common site of neoplastic, vascular, and degenerative diseases, which often demand surgical treatment. 1,2,3,4,5,6,7 Chordomas are rare neoplasm, corresponding of 0.1 to 0.7% of intracranial tumors. 8 They originate from remnants of the notochord, and because of that, they can arise anywhere along the neural axis; however, their most common sites are the sacrum (50%) and the skull base (up to 36%). 8 The first reference of a lesion corresponding to a chordoma is from Virchow in 1846, but it wasn’t until 1925 when Coenen reviewed the first major series of chordomas (68 cases). 8,9
20.1.2 Macroscopical Aspects
As described by Borba et al in 2001, chordomas are soft, gelatinous, grayish to reddish, and generally lobulated avascular tumors that may also present as a cheeselike material, with small islands of tumor; that pattern leads to the infiltration of the bone along the lines of least resistance, making it not possible to delimitated the normal bone from the compromised one. 8
20.1.3 Clinical Aspects
Chordomas are slow-growing lesions and their diagnosis can be delayed, as they don’t produce any pathognomonic symptoms. Like other intracranial tumors, their clinical manifestations will be directly related to the adjacent compromised structures. 8,10,11 The most common signs and symptoms are neuro-ophthalmologic disturbance, headache, and hypoglossal nerve palsy. 10,11,12
20.1.4 Selecting the Approach
Because of their deep location on the skull base and growing pattern, approaching these lesions can turn into a real challenge even to the best-trained surgeons. Their locations and extension through the skull base will be the defining factors on choosing the most suitable approach. 11,12,13,14 Since the introduction of the posterolateral approaches to the craniovertebral junction, many modifications have been proposed in order to reduce retraction of neurovascular structures and allow maximum exposure. 1,4,15 These variants mainly consist of extensions of the far-lateral approach, in which there is no condyle removal, and their anatomical aspects were well established in the study reported by Wen et al in 1997. 13 Because of its versatility, many authors have been using the far-lateral approach and its variations over the years, sometimes in association with other approaches to provide a wider exposure. Eventually, even when a wide exposure is gained, multiple interventions can be required to achieve maximum tumor resection. The indications for consecutive procedures are based on the preoperative tumor extension and the amount of residual lesion after the first operation. 10,11,12 In the series reported by Al-Mefty and Borba in 1997 with 23 patients with skull base chordomas operated between 1990 and 1996, a single-step procedure was performed in 17 patients and 6 patients were submitted to a second procedure.11 The most frequently used approaches were the cranio-orbital-zygomatic (six cases) and extended transsphenoidal (five cases). The transcondylar approach was used in four cases. Including all the approaches that were used, gross total resection was obtained in 10 cases (43.5%), subtotal resection in 11 cases (47.8%), and partial resection in 2 cases (8.7%). Later, Sen et al in 2010 reported 39 procedures in 29 patients with skull base chordoma, treated between 1991 and 2007, of which, 19 patients were treated with a single-step resection and 10 patients underwent a second procedure using combined approaches.12 The most used approaches were the extreme lateral transcondylar (19 cases), expanded endoscopic endonasal (5 cases), and transmaxillary (4 cases) approaches; gross total removal was achieved in 17 cases (58.6%), subtotal removal in 10 cases (34.4%), and partial tumor removal in 2 cases (6.8%).
20.2 Indications and Limits
The transcondylar approach can be used to reach chordomas of the inferior third of the clivus, with or without lateral extension to the craniovertebral junction or upper cervical vertebrae. 11,12,13,14,15 The limits of the transcondylar approach are the nasopharynx anteriorly, the spinomedullary junction posteriorly, and the jugular bulb and XII nerve superiorly ( ▶ Fig. 20.1). The inferior limit is tailored to each patient, as the skin incision can be as low as necessary. 14 The main advantages of this approach are the safe exposure of the space anterior to the neuroaxis and the ability to attack the lesion in a parallel plane. Besides, the surgical corridor is short, wide, and sterile, and stabilization, if needed, can be performed via the same exposure. 14,15 In this chapter, we present the technique and major anatomical aspects of the transcondylar approach we use to treat clival chordomas, along with its indications, limits, and possible complications.
Fig. 20.1 Anatomical limits of the transcondylar approach: the spinomedullary junction (SMJ), the hypoglossal nerve (XII), and the jugular bulb (JB). The occipital condyle was partially removed (white asterisk), exposing the hypoglossal canal (white dashed circle). Also notice the transverse process of C1 (C1t) and the horizontal segment of the vertebral artery (VAh).
20.3 Preoperative Assessment
Radiologic investigation is performed with computerized tomography (CT) scans with thin cuts, so that bone structures can be studied, and the dynamic studies can be performed with magnetic resonance imaging (MRI) with the patient in extension and flexion positions. Prior to surgery, electrodes for intraoperative monitoring are placed. These include bilateral somatosensory evoked potentials, bilateral brainstem auditory evoked response, and cranial nerve X, XI and XII monitoring. Neuronavigation can also be a useful tool.
20.4 Surgical Technique
20.4.1 Patient Positioning
Patient is positioned in lateral decubitus with the head fixed on a three-pin Mayfield device and placed parallel to the floor. Cushions are placed under the contralateral armpit to protect the brachial plexus and between the knees to reduce contact pressure. The contralateral arm rests out and below the surgical table and must be flexed in about 30 degrees in order to maintain the venous return of that limb ( ▶ Fig. 20.2 a). The ipsilateral shoulder is displaced slightly inferiorly (care must be taken not to damage the brachial plexus) ( ▶ Fig. 20.2 b). The ipsilateral thigh should be prepared before the beginning of surgery for possible fascia lata and fat harvest.
Fig. 20.2 (a) Patient in lateral decubitus. Cushion under the contralateral armpit (black arrow), which rests out and below the surgical table with 30 degrees flexion (black dashed arrow); notice how that arm is protected from the contact with any metal parts of the table and head-fixing device. Head parallel to the ground (red dashed line). (b) The ipsilateral shoulder slightly displaced inferiorly (black arrow). (c) Skin incision center (black asterisk) is parallel (white dashed line) to the mastoid tip (red dashed triangle). Incision extends to the anterior border of sternocleidomastoid muscle (black dashed line).