Chordomas are quite rare pathological entities occurring with an overall incidence rate of 0.08 per 100,000 [24, 26, 44, 47, 49]. They may occur at any age, although they are most commonly encountered in male patients during the third, fourth, and fifth decades of life and rarely appear in children (<5 %). Chordomas histologically derive from remnants of embryonic notochordal tissue a rodlike cord of cells from which the skull base and vertebral column develop [26, 32, 44, 46]; indeed, they can arise anywhere along the axial skeleton – nearly always within the bone – having a predilection for the sacrum, clivus, or cervical vertebrae [24, 26, 32, 44, 47, 57]. In rare cases (3–7 %), they arise from the cervical spine (cervical chordomas), presenting as a paravertebral or parapharyngeal mass [24, 26, 42, 44, 64].

Almost a third of chordomas arise at the skull base (cranial chordomas) involving the clival area [26, 32, 46, 57]. These tumors are typically slow growing, with an indolent but progressive clinical course; they can be assumed as malignant but classified as tumors of low to intermediate malignancy with a propensity for locally aggressive behavior [14, 22, 26, 32, 49, 57].

Chordomas figure out as midline, usually extradural, masses originating within the bone and, grossly, appear as gelatinous, soft blue-gray multilobulated masses; sparse areas of hemorrhage, cystic and/or necrotic degeneration, or calcification may be encountered. If on one hand these lesions are often well circumscribed at surgical exploration, on the other hand they show a certain degree of local invasiveness with destruction of the adjacent bone and eventual dural invasion. Although there cannot be clearly identified features depicting lesion aggressiveness, several molecular markers could be associated with an aggressive biologic behavior [32, 44].

According to the WHO classification, there have been defined three histopathologic patterns of chordoma: classic or conventional, chondroid, and dedifferentiated [5, 26, 36, 44, 50, 51, 54, 64].

The conventional chordoma is the most frequent diagnosed lesion: this histotype accounts for islands and cords of eosinophilic and clear vacuolated cells immersed in a basophilic myxoid/mucoid background. Thin fibrous septa can be recognized dividing groups of cells into lobules. Above all, it should be said that this histotype is identified with the most representative microscopic aspect: the majority of cells are vacuolated, so it have been called “physaliphorous cells” (from the Greek word meaning bearer of bubbles). Eventual areas of necrosis seem to draw a more aggressive course, whereas scattered mitoses, nucleoli, vascular invasion, and nuclear pleomorphism seem to not affect the tumor’s prognosis. Usually no chondroid or other mesenchymal tissue differentiations are observed [5, 26].

The second histologic pattern of chordomas is defined by the presence of clear chondroid differentiation, however to be not interpreted as evidence of cartilaginous differentiation. This so-called chondroid chordoma is usually related to a better prognosis, although several authors have advocated that this better outcome could be associated with patient age rather than with the histopathologic development. At microscopy there is a resemblance of this tumor with low-grade chondrosarcoma [36, 54].

Finally, the third histologic class of identifies malignant chordomas, which present a frank mesenchymal component. This aspect constitutes the basis for the diagnosis of dedifferentiated chordomas; the prognosis is very poor and this tumor leads to death within a year. Hematogenous metastases consisting entirely of sarcomatous elements are common; contrariwise, other patterns of chordomas rarely result in metastasis [14, 42, 50, 52].

Despite the distinctive appearance of most chordomas, there are several important considerations that could be drawn in terms of differential diagnosis: chordomas may be confused with skull base chondrosarcomas, chordoid meningiomas, extraskeletal myxoid chondrosarcomas, metastatic mucinous adenocarcinomas, and, a developmental lesion, ecchordosis physaliphora. Most of them present at direct pathological observation many characteristics similar to the chordomas that could mislead diagnosis. However, according to peculiar features, chondrosarcomas differ for negative cytokeratin, as well as extraskeletal myxoid chondrosarcomas. Metastatic mucinous adenocarcinomas are usually negative for S-100 protein and, finally, ecchordosis physaliphoras are easily distinguished by their inferior size, complete lack of osseous components, and benign clinical behavior [26, 32, 47, 50, 51, 57, 62, 64].

When considering radiological appearance, cranial base chordomas on high-resolution computed tomography and magnetic resonance imaging (MRI) can be identified as well-circumscribed, soft tissue masses arising from the clivus and are accompanied by lytic bone destruction. They are isointense on T1-weighted MRI scans and usually post GAD enhancement. On the T2-weighted MRI scans, a hyperintense signal, per bone erosion areas, is observed; chondroid chordomas eventually may present intratumoral calcification [14, 26, 32, 42, 44, 49].

Case history of chordomas is very insidious, with patients that complain of general symptoms as headache, dizziness, and lower limb paresthesia for months/years before medical attention is drawn; when cranial nerve involvement is present, especially the abducens nerve (cranial nerve VI), often it figures out as presenting sign. Seldom, cerebellar syndrome, local neck pain, brainstem syndrome, and/or lower cranial nerve palsies could be present, especially when lesion involves the lower aspect of the clivus [10, 26, 32, 42, 44, 46, 52, 53, 57].

Chordomas pose significant challenges for cranial base surgeons: their central location and their tendency to infiltrate the bone render total removal rarely possible; moreover such tumors are associated with a high incidence of recurrence [7, 14, 16, 22, 26, 42, 44, 49, 51, 55, 62, 64]. Indeed, the achievement of total resection at primary surgery determines a tremendous improvement in 5-year survival rate, whereas it fell down in case of partial removal [1, 17, 26, 32, 40, 57–59]. Besides, it has to be underlined that their proximity to vital neurovascular structures, including cranial nerves and the brainstem, carries significant potential for severe postoperative morbidities. It clearly stands though that the optimal operative approach should offer the best chance of radical removal while minimizing the potential for postoperative complications [1, 16, 17, 21, 23, 42, 55, 61].

Historically, different extensive and complex skull base approaches have been described for the resection of clival chordomas, thus providing neurosurgeons with a wide choice of surgical strategy of accomplishing radical removal [6, 17, 31, 49, 50, 55, 56, 62]. Because chordomas are mainly extradural and midline tumors that displace dorsally the neurovascular structures, ventral corridors have been preferred: indeed, in transfacial [3, 13, 20, 35, 45, 60], transsphenoidal [2, 15, 25, 30, 40, 42, 44, 46, 52, 57], and transoral [11, 19, 34] techniques, lesions have been defined and renewed along with the technological progress and surgical technique refinements.

Al–Mefty and Borba [1] introduced a surgical classification of skull base chordomas as related to their local extension: type I that includes lesions limited to one clival compartment, which are rare; type II that comprises two or more contiguous areas; and type III, in which the lesion extends into several compartments and more than one surgical procedure is necessary. Though, several factors – i.e., location, involvement of the bone and eventually of the occipital condyles, and craniocervical instability – have to be considered in detail when choosing the proper surgical management. Furthermore, it has to be said that in this era of minimally invasiveness, adjunctive proton beam treatment and maximum possible removal have been claimed as viable strategy to achieve a longer and better tumor control [4, 9, 16, 27, 33, 42, 44, 48, 61, 63].

In more recent times, the increasing use of the endoscope in transsphenoidal surgery has allowed the endonasal route to be considered for the management of lesions of the cranial base, thus unlocking new possibilities for skull base surgery [8, 12, 18, 37–39, 43]. This technique allows a wide and median exposure of the targeted area, with a more orientable and closeup view, while obviating brain retraction. The wider and panoramic view offered by the endoscope and the rapid growth of neuroradiological diagnostic techniques together with the intraoperative neuronavigation systems has expanded its applicability to the removal of skull base chordomas [10, 26, 28, 29, 40, 41, 59].

We herein present the surgical nuances – according to our experience – of the endoscopic endonasal approach in the treatment of chordomas, aiming to highlight the feasibility of this technique and evaluate its advantages and limitations.