Endoscopic assisted minimally invasive resection of petrous bone epidermoid cyst via a presigmoid burr hole approach: illustrative case

Abstract

BACKGROUND

Intracranial epidermoid cysts are rare congenital lesions accounting for approximately 1% of intracranial tumors. Petrous apex involvement is uncommon and surgically challenging because of the lesion’s proximity to critical neurovascular structures. Reports describing minimally invasive endoscope-assisted approaches in this location remain limited.

OBSERVATIONS

A 32-year-old man presented with progressive right-sided otalgia, pulsatile tinnitus, and hearing loss. Imaging demonstrated a destructive petrous temporal bone lesion with atypical diffusion characteristics, initially suspected to represent a jugular foramen tumor. The patient underwent a minimally invasive endoscope-assisted presigmoid burr hole approach. Intraoperatively, the lesion demonstrated the characteristic pearly appearance of an epidermoid cyst and was resected piecemeal under microscopic and endoscopic visualization. Endoscopic assistance improved visualization of deep and angled extensions beyond the microscopic field. Postoperatively, the patient had preserved facial nerve function, stable hearing, and an uneventful recovery. Histopathological examination confirmed an epidermoid cyst.

LESSONS

Petrous apex epidermoid cysts require balancing maximal safe resection with preservation of neurological function. This case highlights the potential utility of a minimally invasive endoscope-assisted approach for improving visualization within constrained skull base corridors while minimizing operative morbidity. Long-term radiological surveillance remains important when complete capsule removal is not safely feasible.

https://thejns.org/doi/10.3171/CASE26361

Intracranial epidermoid cysts constitute approximately 1% of all intracranial tumors.^1,2 Congenital rests of epithelial tissue deposited in the petrous apex during development lead to formation of epidermoid cysts of the petrous apex. Histologically similar to middle ear and mastoid cholesteatoma, petrous apex epidermoid cysts are epithelial cysts that exist medial to the optic capsule. Although epidermoid cysts are not themselves malignant lesions, progressive growth may result in local bony destruction and invasion of critical neurovascular structures.³ Because of their location within the medial skull base, they can grow to large sizes and invade many structures before becoming clinically evident. Most (50%–60%) commonly reside in the cerebellopontine angle, followed by the parasellar or suprasellar region, the fourth ventricle, and less often intraparenchymal or intraventricular locations.^4,5 Many publications have discussed the surgical management of cerebellopontine angle epidermoid cysts, but few have focused exclusively on epidermoid cysts arising within the petrous bone.^1,3–5 The behavior of these cysts usually causes them to encircling cranial nerves and arteries, especially cranial nerves V–VIII, which makes surgical dissection challenging and dictates a strategy of delicate capsule peeling. Fortunately, an epidermoid cyst capsule usually remains extra-axial and avascular, and an arachnoid membrane often partially separates the cyst from the brainstem or cranial nerves.^6,7 To our knowledge, reports describing minimally invasive endoscope-assisted burr hole approaches for petrous temporal bone epidermoid cysts remain limited in the literature.

Illustrative Case

A 32-year-old previously healthy male was admitted for evaluation and surgical management of a presumed right jugular foramen lesion, initially suspected radiologically to represent a glomus jugulare tumor. He presented with a 2-year history of progressive right-sided ear pain, pulsatile tinnitus, and decreased hearing. His past medical history was significant only for irritable bowel syndrome, with no prior surgical history. On examination, the patient had a negative Rinne test on the right side (indicating bone conduction > air conduction) and a Weber test lateralizing to the right side. Examination of the rest of the cranial nerves was unremarkable. Motor, sensory, and coordination examination of the upper and lower extremities was unremarkable. A preoperative CT study of the brain was performed (Fig. 1) and showed a destructive lesion in the right petrous bone arising at the upper portion of the jugular bulb and extending anteriorly to the carotid canal. Moreover, preoperative MRI of the brain was done (Fig. 2) and showed a large nonenhancing lesion within the region of the right jugular with high signal intensity on T2-weighted, fluid-­attenuated inversion recovery (FLAIR), and diffusion-weighted imaging (DWI). Correlation with apparent diffusion coefficient (ADC) imaging showed no diffusion restriction. Given the lesion’s focal localization within the posterior petrous temporal bone adjacent to the jugular foramen, an endoscope-assisted minimally invasive presigmoid burr hole approach was selected to provide a direct surgical trajectory while minimizing soft tissue dissection and cerebellar retraction. Alternative approaches considered included retrosigmoid and translabyrinthine skull base approaches; however, these were considered less favorable given the lesion configuration and the goal of hearing preservation.

FIG. 1.

Preoperative axial (A), coronal (B), and sagittal (C) CT scans of the brain without contrast, showing the destructive lesion (arrows) in the right petrous bone arising at the upper portion of the jugular bulb and extending anteriorly to the carotid canal. Medially, the lesion causes mild mass effect on the right cerebellar cortex with no definite intracranial extension. Laterally, the lesion partially extends into the middle ear cavity (hypotympanum). Axial (D) and coronal (E) bone windows showing no extension into the external auditory canal. The foramen magnum is intact. The lesion is causing destruction and widening of the jugular foramen. It appears heterogeneous in density with cystic changes and measures approximately 2 × 1.9 × 2.4 cm in diameter (transverse, anteroposterior, and craniocaudal, respectively).

FIG. 2.

Preoperative MR images of the brain with contrast, showing a large lesion mass (arrows) within the region of the right jugular foramen. Axial (A), sagittal (B), and coronal FLAIR (C) T2-weighted MR images showing bright signals. The tumor extends beyond the margins of the jugular foramen and involves the temporal bone, showing destructive changes. The tumor size measures 2.7 × 4.2 × 3.5 cm in diameter (transverse, anteroposterior, and craniocaudal, respectively). Axial ADC (D) and diffusion-weighted (E) images showing normal signal and high signal, respectively, and thus no diffusion restriction. T1-weighted axial (F) and coronal (G) MR images with contrast, showing that the lesion is hypointense and not associated with any enhancement on the postgadolinium images. Normal flow voids or vascular signal is detected within the tumor.

The patient was placed in a park-bench position with the right side up. A 2-cm linear incision was made 2 cm behind the ear. A 10-mm burr hole was done, and mastoid air cells were entered. The patient was already registered with neuronavigation, and preoperative CT-based anatomical planning was used to define a trajectory posterior to the labyrinth and lateral to the sigmoid sinus while avoiding the anticipated course of the facial nerve within the temporal bone. Fusion of CT and MR images assisted in localization of the lesion relative to the cochlea, semicircular canals, carotid canal, and jugular bulb. Hearing preservation was prioritized given the patient’s residual preoperative auditory function, and therefore a translabyrinthine route was avoided. The burr hole was deepened under neuronavigation guidance with a drill to enter the destructive lesion in the petrous bone, and the opening was widened from inside (Video 1). The tumor was clear and pearly, suggesting an epidermoid cyst. The lesion was excised in piecemeal fashion with a microscope, emptying its contents, and the capsule was visualized (Fig. 3A). After reaching the cyst capsule under microscopic visualization, the endoscope was introduced (Fig. 3B and C) to assess the depth and superior-inferior and anterolateral extent of the lesion resection. Continuous intraoperative facial nerve monitoring was utilized throughout the procedure because of the lesion’s proximity to the facial nerve canal and lower cranial nerves. Hearing preservation remained an important surgical objective given the patient’s residual auditory function. The remaining accessible deep cyst contents and portions of the capsule were excised with endoscopic assistance while carefully preserving adjacent neurovascular structures. Aggressive capsule dissection was intentionally avoided in regions where adherence to critical structures could increase the risk of neurological morbidity. The cavity was packed with Gelfoam. The dura was intact, there was no CSF leakage, and adjacent neurovascular structures remained intact. The bone opening was covered with a small burr hole cover and mini screws. The wound was closed subcutaneously and the skin layer was closed with absorbable Monocryl sutures. The patient tolerated the procedure well, was extubated in the operating room, and was shifted to recovery in stable condition. Postoperative CT of the brain (Fig. 4) showed the expected postoperative changes after right presigmoid craniotomy and tumor resection. The patient remained well postoperatively with intact facial nerve function and stable hearing compared to his preoperative status. He was discharged home in good condition on postoperative day 2 with outpatient follow-up appointments. Histopathological examination demonstrated keratinaceous debris consistent with an epidermoid cyst, with no evidence of malignancy, confirming the diagnosis (Fig. 5A and B).

FIG. 3.

Intraoperative views of the surgical procedure. A: Microscopic view demonstrating the characteristic pearly white appearance of the epidermoid cyst (arrow) during early piecemeal resection. B and C: Endoscopic views following introduction of the endoscope to assess lesion depth and superior-inferior and anterolateral extent. The deep cyst contents (arrow) were removed in a piecemeal fashion (B), and the capsule (arrow) was identified and completely excised with endoscopic assistance.

FIG. 4.

Postoperative axial (A), coronal (B), and sagittal (C) CT scans of the brain without contrast, showing postoperative changes in the form of right retrosigmoid mild subcutaneous emphysema, soft tissue swelling, and minimal hyperdense blood products along the surgical margin (arrows), as well as small subgaleal soft tissue thickening/hematoma measuring up to 0.4 cm and opacification of the right hypotympanum and inferior mastoid air cells. Axial (D) and coronal (E) bone windows showing the surgical bed (arrows) along with destruction and widening of the right jugular foramen.

FIG. 5.

Histopathological examination using hematoxylin and eosin staining, demonstrating keratinaceous debris consistent with an epidermoid cyst. A: Low-power view (×4 magnification) showing keratin flakes (arrows). B: Higher-power view (×10 magnification) demonstrating keratin flakes with associated calcified debris (arrows).

VIDEO 1. Intraoperative video demonstrating an endoscope-assisted minimally invasive resection of a petrous bone epidermoid cyst via a presigmoid burr hole approach. Hx = history; O/E = on examination. Click here to view.

Informed Consent

The necessary informed consent was obtained in this study.

Discussion

Observations

Intracranial epidermoid cysts are rare congenital inclusion lesions, comprising approximately 1% of all intracranial tumors, with petrous apex involvement representing an uncommon and diagnostically challenging subset.⁶ Their slow growth, tracking along subarachnoid spaces and skull base corridors, often permits significant expansion before clinical manifestation, frequently resulting in osseous erosion and close association with critical neurovascular structures.^7,8

Radiologically, these lesions may mimic other skull base pathologies, particularly in the jugular foramen region, as seen in this case, in which the initial working diagnosis favored a glomus tumor.^5,9 Advanced imaging characteristics, including signal behavior on DWI, may aid in differentiation but are not always definitive preoperatively.^5,10

The radiological differential diagnosis in this case included epidermoid cyst, glomus jugulare tumor, and cholesterol granuloma. The absence of contrast enhancement and lack of internal vascular flow voids argued against a highly vascular paraganglioma, while the lesion’s destructive osseous changes and atypical diffusion characteristics complicated preoperative diagnosis. Although epidermoid cysts classically demonstrate diffusion restriction, atypical diffusion patterns have been described in lesions with altered keratin composition or heterogeneous cyst contents. In selected equivocal skull base lesions, advanced adjunctive imaging such as somatostatin receptor imaging with DOTATATE PET may further assist in differentiating paragangliomas from nonneuroendocrine lesions.

Microsurgical resection remains the cornerstone of therapy for intracranial epidermoid cysts.⁶ The operative approach is indicated based on the lesion’s location and extent. For CPA tumors, a lateral suboccipital retrosigmoid craniotomy is the main approach, providing access to the cerebellopontine cisterns.⁷ Lesions in the parasellar or middle fossa region are often approached via a pterional craniotomy, sometimes combined with orbitopterional or transsylvian dissection to reach prepontine extensions. Deep midline tumors, affecting the fourth ventricle or vermian, may require a midline suboccipital approach.⁷

The primary goals are relief of neural compression and prevention of cyst regrowth. Most patients achieve meaningful symptomatic improvement after surgery. In a recent series, 41%–43% of patients who underwent total resection had improvement in their preoperative neurological symptoms at the 1-year follow-up, compared to 28% improvement in those with subtotal resection.⁸ Even when new postoperative deficits occur, such as transient cranial nerve palsies, they tend to improve over time in many cases.⁸ A meta-analysis by Samii et al. noted recurrence rates ranging from 1% to 54% when any capsule is left versus very rare recurrence after total removal.⁹ In practical terms, this means that if a bit of the capsule is deliberately left on a cranial nerve, one must anticipate the possibility of regrowth in future decades and thus perform regular MRI surveillance. Even with benign histology, intracranial epidermoids can be associated with significant surgical morbidity because of their complex anatomy.

Selection of the operative corridor for petrous temporal bone lesions must be individualized according to lesion location, extension, hearing status, and relationship to neurovascular structures. Conventional approaches for petrous apex and cerebellopontine angle epidermoid cysts include retrosigmoid, translabyrinthine, middle fossa, and combined skull base approaches. Retrosigmoid approaches provide broad access to the cerebellopontine angle but may require greater cerebellar retraction for anterior petrous lesions. Translabyrinthine approaches offer direct exposure of the petrous region but sacrifice hearing and therefore may not be ideal in patients with serviceable auditory function. In the present case, the lesion was well localized and directly accessible through a targeted presigmoid corridor, permitting a minimally invasive trajectory with neuronavigation guidance while preserving hearing structures.

From a surgical perspective, the lesion’s location within the petrous temporal bone introduces additional complexity due to restricted access corridors and proximity to the facial nerve, cochlear structures, and lower cranial nerves.⁵ In this case, a minimally invasive presigmoid burr hole approach allowed targeted entry into the lesion with the assistance of neuronavigation. Piecemeal evacuation of the cyst contents under microscopic and exoscopic visualization revealed the characteristic pearly appearance of an epidermoid cyst, with identification of the capsule.

The adjunctive use of the endoscope enabled further inspection of the resection cavity beyond the direct line of sight of the microscope, particularly along the superior-inferior and anterolateral extensions. Postoperatively, the patient demonstrated preservation of facial nerve function and stable hearing, suggesting that a limited-access approach can be used without compromising functional outcomes in selected cases.

Potential advantages of this minimally invasive endoscope-assisted approach include reduced soft tissue dissection, limited craniotomy size, decreased cerebellar manipulation, and improved angled visualization within deep skull base corridors. Endoscopic assistance may facilitate identification of residual cyst contents beyond the direct microscopic line of sight. However, minimally invasive corridors may also restrict instrument maneuverability and limit aggressive circumferential capsule dissection in regions adherent to critical neurovascular structures. Consequently, meticulous surgical planning and careful patient selection remain essential.

Lessons

Management of petrous temporal bone epidermoid cysts requires balancing maximal safe resection with preservation of neurological function because of the lesion’s close relationship to the facial nerve, vestibulocochlear apparatus, and surrounding neurovascular structures.

This case highlights the role of endoscope-assisted microsurgical techniques in minimally invasive approaches, where angled visualization may improve assessment of residual tumor within deep or complex extensions beyond the microscopic field. A neuronavigation-guided minimally invasive presigmoid burr hole corridor may offer effective access in selected well-localized lesions while limiting soft tissue dissection and operative morbidity.

Intraoperative facial nerve monitoring remains essential during resection. Although minimally invasive corridors may reduce approach-related morbidity, they can also limit maneuverability for aggressive circumferential capsule dissection. Consequently, the goal should remain maximal safe resection rather than radical capsule removal when adherence to cranial nerves or vascular structures is encountered.

Overall, this case highlights the importance of tailoring the surgical strategy to the lesion’s anatomy while balancing maximal safe resection with preservation of neurological function. A minimally invasive endoscope-assisted approach may improve visualization and facilitate resection within constrained skull base corridors; however, surgical decision-making should remain individualized, with priority given to functional preservation and long-term surveillance when complete capsule removal is not safely feasible.

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: Hafiz, Turkistani, Muzian, Aref. Acquisition of data: Hafiz, Turkistani, Muzian. Analysis and interpretation of data: Hafiz, Turkistani, Aref. Drafting the article: Hafiz, Turkistani, Muzian, Aref. Critically revising the article: Hafiz, Turkistani, Khalid. Reviewed submitted version of manuscript: Hafiz, Turkistani, Muzian, Mokhtar. Approved the final version of the manuscript on behalf of all authors: Hafiz. Administrative/technical/material support: Aref. Study supervision: Hafiz, Aref. Pathology images and legends: Mokhtar.

Supplemental Information

Videos

  Video 1. https://vimeo.com/1197406901.

Correspondence

Badr Hafiz: King Faisal Specialist Hospital and Research Centre, Jeddah, Kingdom of Saudi Arabia. neurosurg.badr@gmail.com.