A multicorridor strategy including the infralabyrinthine route for extensive skull base chondrosarcoma: illustrative case

Abstract

BACKGROUND

Skull base chondrosarcomas (SBCs) are rare tumors with limited responsiveness to chemotherapy and radiation therapy, making surgery the primary treatment option. In cases in which lesions widely extend from the middle cranial fossa to the petrous bone, jugular foramen, and extracranial skull base, no single approach can achieve sufficient exposure or safety margins. A multicorridor strategy can enable safe resection in such cases, even for large and complex tumors; this involves selecting the optimal approach for each anatomical region and simultaneously performing anterior and posterior approaches.

OBSERVATIONS

A woman in her 50s had a chondrosarcoma involving five distinct regions: the cavernous sinus/Meckel’s cave, petroclival-petrous area, jugular foramen, cerebellopontine angle, and extracranial skull base. A single-stage, simultaneous anterior-posterior approach combining the transcavernous, anterior transpetrosal, presigmoid infralabyrinthine, and transjugular–condylar fossa corridors enabled > 95% tumor resection with complete cranial nerve preservation.

LESSONS

In cases of SBCs with broad, multidirectional extension, integrating multiple anatomically tailored surgical corridors with a simultaneous anterior-posterior approach can achieve maximal exposure while maintaining safety. In particular, the infralabyrinthine corridor was valuable for providing secure access to the jugular foramen and deep petroclival regions, serving as a crucial link between the combined approaches.

https://thejns.org/doi/10.3171/CASE2618

Skull base chondrosarcoma (SBC) is a rare tumor that accounts for only 0.15% of all intracranial neoplasms.^1–3 These tumors are histologically classified as WHO grades 1–3, with most being low-grade with slow growth.^1,4,5 However, because SBCs arise in close proximity to the complex neurovascular structures of the skull base, their enlargement can result in severe cranial neuropathies and other significant neurological deficits.^6,7 Furthermore, SBC is relatively resistant to both radiotherapy and chemotherapy,^6,8,9 while emerging molecular therapies such as IDH1 inhibitors and immune checkpoint inhibitors remain investigational.¹⁰ In such cases, the primary treatment goal is maximal safe resection while preserving neurological function.

Primary SBCs most commonly originate from petroclival, petro-occipital, spheno-occipital, or sphenopetrosal synchondroses. Approximately 64% occur in the middle cranial fossa, whereas only 7% occur in the posterior fossa, which represents the rarest site.^11–14 Among these, tumors arising from the jugular foramen (i.e., posterolateral to the petro-occipital suture at the posterior cranial base) are exceedingly rare. SBCs frequently demonstrate contiguous extension across multiple anatomical compartments, which can span the anterior, middle, and posterior cranial fossae.

Although numerous skull base approaches have been described, tumors that extend across multiple compartments often cannot be adequately exposed using a single approach alone.^1,7,15 Optimal access in such cases can be achieved through the multicorridor strategy, which involves decomposing the tumor into its directional corridors and strategically combining multiple approaches.

This report describes a case of low-grade chondrosarcoma with extensive involvement of the cavernous sinus, middle cranial fossa, petroclival region, jugular foramen, cerebellopontine angle (CPA), and extracranial skull base. Resection was achieved using a multicorridor strategy integrating the transcavernous, anterior transpetrosal, presigmoid, and infralabyrinthine approaches, as well as a transjugular–condylar fossa approach that was applied simultaneously from the anterior and posterior directions. This report also highlights the operative view and role of the infralabyrinthine corridor, which was particularly valuable in this case.

Illustrative Case

Presentation and Preoperative Workup

A woman in her 50s presented with a 6-month history of diplopia during distant gaze. She had no headache, visual field disturbances, facial numbness, or dysphagia. Neurological examination revealed subtle restriction of the right upward gaze and mild right-sided conductive hearing loss; facial nerve function, sensation, swallowing, and tongue movements were intact. She had no remarkable past medical history, family history, or relevant psychosocial background. No prior interventions relevant to the present condition had been performed.

At the referring hospital, MRI revealed a large mass at the skull base, extending from the right cavernous sinus into the middle cranial fossa, petrous apex, and clivus, with posterior extension toward the internal auditory canal (IAC) and CPA, as well as inferior extension toward the jugular foramen (Fig. 1). CT revealed bone destruction of the petrous apex and clivus. A right frontotemporal craniotomy with a subtemporal approach was performed for diagnostic and decompressive purposes, and histological examination confirmed the presence of a WHO grade 1 chondrosarcoma. The postoperative course was complicated by a subcutaneous wound abscess, which required debridement and removal of the infected bone. After the infection completely resolved, the patient was referred to our department for definitive treatment.

FIG. 1.

Preoperative MR images obtained at the referring hospital. A–C: Axial (A), sagittal (B), and coronal (C) gadolinium-enhanced T1-weighted images showing a large skull base tumor and extensive tumor extension in the left maxilla. D–F: FIESTA axial images showing tumor involvement at the pontine level (D), medullary level (E), and condylar level (F), highlighting the relationship between the lesion and structures of the brainstem and skull base.

On admission at our institution, the patient still exhibited diplopia on distant gaze and right-sided conductive hearing loss persisted. However, the lateral gaze, facial sensation, facial nerve function, swallowing, and tongue movements were normal. Otological evaluation of the right ear confirmed mild serous otitis media and conductive hearing loss.

MRI demonstrated a multilobulated mass measuring approximately 6 cm, extending into the following compartments (Fig. 2A–D): 1) cavernous sinus and Meckel’s cave, 2) petrous apex and petrous bone, 3) jugular foramen, 4) CPA posterior to the IAC, and 5) extracranial skull base, lateral to the condyle and hypoglossal canal. The tumor was hypointense on T1-weighted, hyperintense on T2-weighted, and mildly hyperintense on FLAIR MRI with minimal edema and heterogeneous contrast enhancement. CT bone images confirmed extensive erosion along the long axis of the petrous bone, inferior to the IAC (Fig. 3). Digital subtraction angiography revealed no prominent feeding arteries, aside from a small contribution from the meningohypophyseal trunk. The right cavernous and sigmoid sinuses were functionally occluded, with venous drainage primarily through the mastoid emissary vein. Spinal MRI revealed no additional lesions.

FIG. 2.

Pre- and postoperative MR images obtained at our institution. A and B: Preoperative FIESTA axial images at the pontine (A) and medullary (B) levels. C and D: Preoperative coronal T2-weighted images showing extensive skull base involvement. E–H: Postoperative FIESTA axial images revealing marked tumor reduction at the pontine (E) and medullary (F) levels and coronal images (G and H), confirming near-total resection.

FIG. 3.

A–C: Preoperative axial (A), sagittal (B), and coronal (C) noncontrast CT images demonstrating extensive bony erosion. D: Preoperative contrast-enhanced axial CT image showing the petrous segment of the ICA surrounded by the tumor. E: Preoperative 3D CT angiogram illustrating the spatial relationship between the vasculature and tumor. F: Preoperative 3D bone reconstruction highlighting skull base destruction. G and H: Preoperative 3D simulation models of the planned surgical corridors viewed from a medial perspective (G) and an inferolateral perspective (H). Red arrows indicate the transcavernous approach, yellow arrows the anterior petrosal approach, and green arrows the presigmoid, infralabyrinthine, transjugular, and condylar fossa approaches. FM = foramen magnum; JF = jugular foramen; T = tumor.

Since WHO grade 1 chondrosarcomas are relatively radioresistant and the tumor exhibited extensive multicompartment and extracranial extension, the treatment goal for this patient was maximal safe resection. A lumbar drain was placed preoperatively, and a multicorridor approach involving the transcavernous, anterior and posterior transpetrosal, presigmoid, infralabyrinthine, and transjugular routes was planned based on the 3D simulation (Fig. 3F–H).

Surgical Case Description

Multimodal neurophysiological monitoring was performed under general anesthesia, including motor evoked potentials, somatosensory evoked potentials, cranial nerves (CNs) II–XII, extraocular muscle stimulation, and auditory brainstem response. Neuronavigation (StealthStation S8, Medtronic) was also used. Two skull base surgical teams simultaneously performed anterior and posterior approaches (Video 1). To avoid elevated brain pressure during middle fossa surgery, the preoperative lumbar drain was maintained intraoperatively and removed at closure.

VIDEO 1.Intraoperative video demonstrating simultaneous anterior and posterior multicorridor approaches to tumor resection. Selecting the optimal approach for each anatomical region and a simultaneous anterior-posterior approach using a multicorridor strategy can enable safe resection, even for large, complex tumors. The multicorridor strategy involves breaking down the tumor into its directional corridors and strategically combining multiple approaches to provide optimal access. A lumbar drain was placed preoperatively, and a multicorridor approach combining transcavernous, anterior and posterior transpetrosal, presigmoid, infralabyrinthine, and transjugular routes was planned based on 3D simulation (Fig. 3F–H). JB = jugular bulb; LCN = lower CNs; LSC = lateral semicircular canal; PSC = posterior semicircular canal; V2 = maxillary nerve (second division of the trigeminal nerve); V3 = mandibular nerve (third division of the trigeminal nerve); V-VII = vertical (mastoid) segment of the facial nerve. Click here to view.

The patient was placed in a supine lateral position, with the head rotated approximately 80° to the left, slightly vertex down, and secured using a Mayfield clamp. The previous question mark incision was reopened, and two operating microscopes were used for the simultaneous anterior and posterior skull base surgeries.

Transcavernous + Anterior Transpetrosal Approach

The frontotemporal skin flap was reflected anteriorly, while the temporalis muscle was reflected inferiorly. Additional drilling was performed along the sphenoid ridge and middle cranial fossa floor through the prior decompressive craniectomy defect. The superior orbital fissure was exposed and unroofed, and the temporal dura propria was peeled and elevated from the lateral wall of the cavernous sinus. Anterior clinoidectomy was performed.

CN V3 and the greater superficial petrosal nerve were identified in the middle fossa, enabling access to Kawase’s rhomboid, which was completely infiltrated by the tumor. On Doppler ultrasonography, the petrous internal carotid artery (ICA) was localized medial to the junction of CN V3 and the greater superficial petrosal nerve. The anterolateral triangle was opened, providing direct access to the tumor, which was soft and easily removed by suction.

However, dense scarring from the prior surgery limited further expansion of the lateral triangle and restricted medial and inferior dissection toward the CN V3 medial compartment and caudal petroclival region. To safely address the posterior and inferior tumor components, a posterior presigmoid infralabyrinthine approach was utilized; this enabled effective anterior-posterior coordination through integrated working corridors.

Presigmoid + Infralabyrinthine Approach

The incision was extended posteriorly, and cosmetic mastoidectomy was subsequently performed. The fallopian canal (from the geniculum to the mastoid segment) was skeletonized along its entire length using electromyography (EMG) monitoring. The infralabyrinthine triangle was widely opened during surgery. The operative field created via anterior petrosectomy converged with the posterior operative field, thereby forming a continuous anterior-posterior working corridor. The tumor was debulked via suction from the petrous apex toward the clivus. Areas of bony infiltration were drilled with a diamond burr down to the healthy marrow.

A 30° endoscope was introduced from the posterior field, enabling visualization of a deep tumor located medial to V3, which was resected using curved suction and ring curettes. The tumor-embedded vidian nerve was partially preserved for functional reasons.

Transjugular–Condylar Fossa Approach

The bone overlying the jugular bulb was removed to expose the lateral wall, revealing a tumor that filled the jugular foramen through a thin membranous layer. Fascicular structures were encountered caudally. The tumor was removed through the jugular bulb alongside EMG monitoring of CN X.

For inferior extension, the condylar fossa was opened, and the occipital condyle was partially drilled to expose the hypoglossal canal. Bony tumor infiltration around the canal was removed, and the recanalized jugular vein segment was packed with Surgicel and closed with a single 6-0 Prolene stitch.

Presigmoid Intradural Inspection

On opening the dura mater posterior to the IAC, the tumor had a small intradural protrusion. CN VIII was confirmed to have a normal ventral course without extensive intradural progression. The dural defect was plugged with fat and reinforced with an inlay DuraGen patch, followed by watertight closure using 6-0 Prolene suture.

Closure

The resection cavity was packed with autologous fat tissue. The lateral mastoid defect was reconstructed using a titanium plate. Cranioplasty of the frontotemporal defect was not performed since the bone was previously removed due to infection. Two drains were placed, and all layers were closed in a standard fashion.

A thin layer of tumor adherent to the anterior ICA was intentionally preserved, although approximately 95% of the tumor was removed. CNs V, VII, VIII, IX, X, and XI were all preserved. Neurophysiological monitoring remained stable throughout the surgery, with no unexpected bleeding or neurological deterioration.

Postoperative Course

Postoperatively, the patient was admitted to the intensive care unit and remained intubated overnight due to the long operative time and risk of cranial neuropathy. Postoperative CT revealed no hemorrhage (Fig. 4). The lumbar drain was removed early after surgery.

FIG. 4.

A–C: Postoperative axial (A), sagittal (B), and coronal (C) noncontrast CT images confirming adequate decompression without hemorrhage. D–F: Postoperative 3D right lateral (D), inferior (E), and superior (F) bone reconstructions demonstrating the extent of skull base drilling.

On postoperative day (POD) 1, sedation was discontinued. Limb movement was intact, and the patient was successfully extubated. Mild right eyelid swelling was observed. The subcutaneous drain was removed on POD 2, and oral intake was resumed after a normal swallowing evaluation. By POD 3, the preoperative diplopia had completely resolved, and the patient could ambulate independently. She reported right aural fullness. On POD 5, the patient experienced mild temporal pain during mastication but maintained adequate oral intake with a soft diet. Oral iron therapy was initiated due to microcytic anemia (hemoglobin 7.7 g/dL). The facial swelling completely resolved. On POD 8, repeat MRI confirmed > 95% tumor resection (Fig. 2F–H). On POD 12, a repeat swallowing evaluation demonstrated normal vocal fold mobility. On POD 14, hearing and vestibular function were reassessed due to the persistence of aural fullness, although no deterioration or cochlear or vestibular deficits were identified. The symptoms were attributed to mild middle ear effusion and eustachian dysfunction, which both improved. The surgical wounds healed uneventfully, and the patient was discharged on POD 15 with independent ambulation. Cranioplasty was planned as a subsequent procedure.

The final pathology report showed nodular proliferation of atypical cells within a myxoid matrix, consistent with chondrosarcoma, predominantly WHO grade 1 with focal grade 2 features. Immunohistochemistry revealed S100 positivity, brachyury negativity, and a Ki-67 index of 1%–2%.

Informed Consent

The necessary informed consent was obtained in this study.

Discussion

Observations

This patient’s tumor had five distinct compartments, extending from the cavernous sinus and Meckel’s cave to the middle cranial fossa, petrous apex and petrous bone, jugular foramen, CPA posterior to the IAC, and further to the extracranial skull base around the condyle and hypoglossal canal. Managing such cases of SBC with multidirectional extension requires a combination of multiple approaches to achieve comprehensive access while avoiding injury to critical neurovascular structures. Notably, near-total resection was achieved in a single stage in this case.

Although low-grade chondrosarcomas typically demonstrate slow progression with a low incidence of distant metastasis,^6,7 they respond poorly to chemotherapy or radiation therapy, making resection the mainstay of treatment.^6,8–10 Chondrosarcomas arising in the skull base frequently involve multiple compartments, and thus the optimal surgical corridor depends on the tumor location, intra- and extradural extension, and its relationship with the surrounding neurovascular structures. As summarized by Rennert et al.,¹⁵ even if the tumor is limited to the petroclival region, feasible routes include the frontolateral, lateral, posterolateral, posteroinferior, and anterior trajectories, emphasizing the need for a tailored and case-specific strategy.

The frontolateral transcavernous approach enables access to the upper petroclival region,¹⁶ whereas the anterior petrosal and extended middle fossa approaches facilitate exposure of the superior VII/VIII complex.¹⁷ A posterior petrosal approach can create a wide operative corridor to the middle and upper clivus. In particular, the infralabyrinthine approach provides a lateral corridor to the petrous apex and medial compartment of the trigeminal nerve while preserving the labyrinth.¹⁸ Meanwhile, the retrosigmoid and far-lateral approaches enable access to the lower clivus and foramen magnum regions.¹⁹ The endoscopic endonasal approach (EEA) provides direct access to the midline clivus with lateral extension into the pterygopalatine fossa, infratemporal fossa, and lateral petrous apex in certain cases.^20,21 For multicompartment tumors, combining these routes is often the only way to avoid blind spots.

In the present case, the tumor extended across five separate anatomical zones: the cavernous/Meckel’s cave, petroclival-petrous area, jugular foramen, CPA, and extracranial condylar region. The full extent of the tumor cannot be adequately addressed through a single approach. Since the patient had already undergone a previous surgery, maximal cytoreduction in a single stage was preferable to avoid the increased morbidity associated with multiple-stage procedures (e.g., repeated anesthesia and worsening adhesions). Although single-stage resection carries the drawback of a longer operative time,¹⁵ simultaneously gaining access through the anterior petrosal and presigmoid infralabyrinthine approaches can minimize interruptions related to surgical repositioning or redraping, efficiently enabling progression through each compartment.

The infralabyrinthine approach plays a central role in this strategy. This approach involves a lateral route running anterior to the sigmoid sinus and inferior to the labyrinth, which permits access to the jugular foramen while preserving the posterior semicircular canal, facial nerve canal, sigmoid sinus, jugular bulb, and lower CNs.^22,23 Previous studies have described its utility as a safe and feasible extradural corridor in lesions involving the petrous apex and petroclival junction.^23–25 In the present case, the latter characteristic was particularly important. By proceeding medially to the fallopian canal and inferomedially to the posterior semicircular canal while preserving these structures, we were able to establish an infralabyrinthine corridor directed anteriorly toward the petrous apex. This trajectory enabled continuous direct visualization and manipulation of the deep-seated regions extending from the petrous apex to the medial compartment of the mandibular nerve (CN V3), while preserving CNs VII and VIII.

During preoperative planning, an EEA combined with a frontolateral transcavernous approach was carefully considered as an alternative strategy. Lesions extending medially to CN V3 are prone to becoming partial blind spots when approached solely via an anterior craniotomy, often necessitating traction on CN V3, but this carries an associated risk of neural injury. Accordingly, for lesions confined to the petrous apex or the medial CN V3 compartment, a minimally invasive EEA-based strategy can be a reasonable option.²⁶ However, in the present case, the tumor extended beyond the medial CN V3 compartment into the jugular foramen, posterior IAC, CPA, and further into the condylar region and surrounding the hypoglossal canal. To safely and consistently address these regions, a lateral-posterior strategy based on the infralabyrinthine triangle, supplemented with elements of the transjugular–condylar fossa approach, was considered more reliable than an EEA-centered strategy, particularly in terms of secure hemostatic control around the jugular bulb and preservation of the lower CNs.

One disadvantage of the infralabyrinthine approach is that jugular bulb skeletonization or mild caudal mobilization may be needed to expand the extradural working space toward the petrous apex and petroclival junction.^25,26 These maneuvers have been associated with serious complications, including massive venous bleeding, air embolism, venous thrombosis, cerebral edema, and venous infarction.²⁷ In the present case, the jugular bulb was already occluded and did not pose any intraoperative issues. In support of our methods, Cinibulak et al. demonstrated that even without jugular bulb skeletonization, a transmastoid infralabyrinthine approach can provide a safe and effective corridor to lesions of the lower petrous apex and petroclival junction.²⁶

Collectively, these considerations suggest that the presigmoid infralabyrinthine approach should not be limited to lesions of the jugular foramen alone. Instead, it can serve as a versatile working corridor that enables effective and safe manipulation of deep-seated lesions involving the petrous apex, medial CN V3 compartment, and region surrounding the hypoglossal canal. However, this multiportal strategy has inherent limitations. Simultaneously undertaking the anterior and posterior approaches requires at least two surgeons experienced in skull base surgery, which may not be feasible in some centers. Additionally, the patient had undergone a prior decompressive craniectomy, and therefore further craniotomy and closure may have increased the operative complexity and duration. Microscope-based surgery imposes spatial constraints during simultaneous work from both corridors. In future cases, an exoscope can be used to improve shared visualization and technical efficiency.

Lessons

In low-grade SBC, maximal safe resection often requires more than a single surgical approach when tumors extend across multiple compartments. In this case, simultaneous integration of skull base approaches according to the directional extension of the tumor was able to improve operative efficiency while minimizing brain retraction.

In particular, the presigmoid infralabyrinthine approach provided a posterior corridor to the petrous apex and medial compartment of CN V3. This converged with the anterior transpetrosal route and enabled linear access to regions not visible from the anterior approach alone. This configuration enables the safe and consistent management of deep-seated lesions.

Acknowledgments

We thank Enago for English-language editing.

We used ChatGPT (GPT-4, OpenAI) to assist with language polishing, sentence restructuring, and improving clarity of the manuscript text. AI was not used to generate scientific content, analyze data, create figures or tables, or generate references. We reviewed and approved all content and take full responsibility for the manuscript.

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: Mitsuhara, Mitsunobu, Takeda, Sugawara. Acquisition of data: Mitsuhara, Kinoshita. Analysis and interpretation of data: Mitsuhara. Drafting the article: Mitsuhara, Mitsunobu, Takeda. Critically revising the article: Mitsuhara, Kinoshita, Sugawara. Reviewed submitted version of manuscript: Mitsuhara, Takahashi, Kinoshita, Takeda, Sugawara. Approved the final version of the manuscript on behalf of all authors: Mitsuhara. Study supervision: Mitsuhara, Sugawara, Horie.

Supplemental Information

Videos

  Video 1. https://vimeo.com/1163671336.

Correspondence

Takafumi Mitsuhara: Graduate School of Biomedical and Health Sciences, Hiroshima University, Minami-ku, Hiroshima, Japan. mitsuhara@hiroshima-u.ac.jp.