Surgical management of clival lesions presents numerous therapeutic challenges because of the close proximity of surrounding critical structures. With a detailed understanding of the endoscopic endonasal approach and relevant considerations, appropriate lesions can be removed in a safe and minimally invasive manner. Use of this technique as a primary approach represents the standard of care for many lesions at leading skull base centers, although adjunct techniques may be necessary in extensive lesions and those with significant lateral extension.
Key points
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Managing clival lesions using a minimally invasive approach presents numerous therapeutic challenges because of the close proximity of surrounding critical structures, including the basilar artery, brain stem structures, and cranial nerves.
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In leading skull base centers, the surgical management of clival lesions has evolved considerably from aggressive external approaches to endoscopic endonasal approaches in select cases.
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Although chordomas and chondrosarcomas are the most common clival lesions, a broad differential diagnosis should be considered during evaluation of clival lesions.
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Identification of the vidian nerve intraoperatively is of paramount importance, because finding this structure helps keep the surgeon below the internal carotid artery.
Introduction
When the tumors appeared at the base of the skull, death usually followed a history of cranial nerve disturbances with pressure symptoms.
Managing clival lesions using a minimally invasive approach presents numerous therapeutic challenges because of the close proximity of surrounding critical structures, including the basilar artery, internal carotid artery, brain stem structures, and the cranial nerves. Discussing his operative technique in Curetting Tumor at Base of Skull , Dr C.A. Porter detailed surgical steps in the management of a patient with a chordoma in the early twentieth century:
Incision [was] made over [the] growth and colloid like material curetted out with free hemorrhage. [The] curette [was] passed upwards and inwards and large masses of material obtained. The greater part of the base of the skull was denuded and the base bone felt everywhere. Bleeding gradually ceased.
Surgical management of clival lesions has evolved considerably since then, as endoscopic endonasal approaches now represent the standard of care for many lesions at leading skull base centers. Nonetheless, the significant potential for serious neurologic consequences makes an understanding of the complex anatomic relationships encountered exceedingly important. Principles of preoperative work-up, surgical preparation, intraoperative management, and postsurgical care are discussed in this article, with illustrative examples of diagnostic imaging and endoscopic anatomy. In addition, the various disorders presenting as clival lesions are discussed.
Introduction
When the tumors appeared at the base of the skull, death usually followed a history of cranial nerve disturbances with pressure symptoms.
Managing clival lesions using a minimally invasive approach presents numerous therapeutic challenges because of the close proximity of surrounding critical structures, including the basilar artery, internal carotid artery, brain stem structures, and the cranial nerves. Discussing his operative technique in Curetting Tumor at Base of Skull , Dr C.A. Porter detailed surgical steps in the management of a patient with a chordoma in the early twentieth century:
Incision [was] made over [the] growth and colloid like material curetted out with free hemorrhage. [The] curette [was] passed upwards and inwards and large masses of material obtained. The greater part of the base of the skull was denuded and the base bone felt everywhere. Bleeding gradually ceased.
Surgical management of clival lesions has evolved considerably since then, as endoscopic endonasal approaches now represent the standard of care for many lesions at leading skull base centers. Nonetheless, the significant potential for serious neurologic consequences makes an understanding of the complex anatomic relationships encountered exceedingly important. Principles of preoperative work-up, surgical preparation, intraoperative management, and postsurgical care are discussed in this article, with illustrative examples of diagnostic imaging and endoscopic anatomy. In addition, the various disorders presenting as clival lesions are discussed.
Differential diagnosis of clival lesions
Although chordomas are the most common clival lesions, they are not the only disorder identified. A differential diagnosis can have implications in terms of patient counseling and prognosis. Surgical resection is the mainstay of treatment of most lesions, and radiation therapy can be considered either as primary therapy among poor surgical candidates or as adjuvant therapy for aggressive or recurrent disease.
Radiologic Characteristics of Clival Lesions
Differentiating factors affecting imaging interpretation are detailed in Table 1 . Importantly, chordomas usually originate at the midline ( Fig. 1 ) whereas chondrosarcomas are more commonly paramedian ( Figs. 2 and 3 ). Depending on the primary tumor, metastasis to the clivus usually has lower signal on T2-weighted magnetic resonance (MR), compared with greater signaling from chordomas and chondrosarcomas. Lesions originating from the clivus as well as the nasopharynx tend to elevate the pituitary gland, in contrast with invasive pituitary macroadenoma involving the clivus, which surrounds the pituitary and makes discrete identification of the pituitary difficult.
| Lesion | Characteristics |
|---|---|
| Chordoma |
|
| Chondrosarcoma |
|
| Plasmacytoma | Plain radiograph: lytic lesions, clear margins CT: invasive outline MR: T1, isointense MR: T2, hyperintense MR: homogenous uptake with gadolinium |
| Metastasis | MR: T2, depends on origin, but may be hypointense |
| Pituitary adenoma | Epicenter is in sella Does not narrow cavernous carotids (in contrast with meningioma) |
| NPC | Increases pituitary gland (in contrast with pituitary macroadenoma) |
Chordoma
Developing from cells thought to be remnants of the embryonic notochord, clival chordomas can commonly present with nonspecific symptoms such as pain and headaches. Furthermore, patients may present with abducens nerve (cranial nerve VI) deficits caused by the close proximity of Dorello’s canal, trigeminal nerve (cranial nerve V) involvement, and in some cases lower cranial nerve deficits. In more advanced disease, there can also be cerebellopontine angle extension ( Fig. 4 ). Analysis of population-based resources such as the Surveillance, Epidemiology, and End Results (SEER) database reveals that chordomas occur predominantly among men more than 40 years of age, and have an incidence of 0.08 per 100,000 people. Younger patients are more likely to have intracranial and clival lesions, and the overall 5-year survival rate has been reported to be 65% to 67.6%, which is significantly worse than patients with ventral skull base chondrosarcoma. Although chordomas are technically considered a low-grade neoplasm and metastasis is exceedingly uncommon, they are usually locally aggressive, with significant clinical sequelae caused by the close proximity of surrounding structures.
Chondrosarcoma
Arising from endochondral cartilage found within the base of the skull, chondrosarcomas most commonly originate spontaneously, although an association has been suggested in patients with Paget disease and osteochondromas. These lesions comprise as much as 6% of ventral skull base tumors, with a recent review of the literature encompassing 560 intracranial chondrosarcomas noting a plurality (32%) of tumors being associated with the clivus. Hence, diplopia, headaches, and other sequelae related to brainstem compression are the most common presenting complaints. The 5-year survival is nearly 90%, with a median survival of 2 years. It has also been noted that there are differences in recurrence rate depending on single modality (surgical) management versus surgery and adjuvant radiotherapy (44% vs 9%). Chondrosarcomas are graded from I to III based on the level of dedifferentiation, with the mesenchymal and conventional subtypes being the histologic variants found intracranially. No statistical difference in recurrence was noted on evaluation of tumors by histologic grading, although mesenchymal subtype tumors have a markedly increased recurrence rate (63%) relative to conventional tumors (16%). A significant proportion of studies comprising these aforementioned percentages contained patients operated on before the recent development and popularization of endoscopic endonasal resections for these lesions.
Plasmacytoma
Although exceedingly uncommon, plasmacytomas of the clivus have been reported in the literature and may be a challenging diagnosis. These lesions have ambiguous presentations, and may be difficult to discern radiologically ( Fig. 5 ). They may present with many of the same cranial neuropathies and related sequelae characteristic of other clival lesions. Formed by monoclonal proliferation of plasmocytes, these represent an underappreciated consideration in the differential diagnosis of clival lesions, and present as solitary lesions in contrast with multiple myeloma, which is a multifocal/disseminated entity; however, they do harbor a risk of progression to multiple myeloma. Intracranial plasmacytomas progress to multiple myeloma in less than a third of cases, whereas solitary lesions elsewhere in the body have progression rates exceeding 50%. One case series revealed that patients had preoperative imaging indicating clival destruction on computed tomography (CT) that was strongly enhancing on MRI; lesions were isointense on T1 MRI and ranged from isointense to hyperintense on T2 MRIs. These lesions are frequently misdiagnosed as other conditions, such as pituitary adenomas or chordomas (see Fig. 5 ). Note that, because of their high level of radiosensitivity in other locations, radiation therapy is the optimal treatment. Nonetheless, these represent diagnostic challenges and may often be operated on as a result. On histology, immunohistochemical staining is positive for CD138 and CD38, and in many cases CD56. Importantly, proliferation is restricted to immunoglobulin light chains, supporting a clonal cause.
Metastasis
Metastasis to the clivus represents another uncommon but underappreciated consideration. Although this should be low on the differential diagnosis, there have been cases reported in the literature. In one review of 47 cases involving metastatic disease to the clivus, this was often the initial presentation of a malignancy elsewhere. Abducens nerve palsy was noted to be the most common specific presenting symptom (61.9%). The most common causes identified were prostate cancer, hepatocellular carcinoma, and thyroid follicular carcinoma. Hence, completing a review of symptoms may be essential to raise suspicion for a primary lesion elsewhere. Furthermore, this diagnosis should be strongly considered in patients with a personal history of malignancy ( Fig. 6 ).
