Strangulation of the abducens nerve by an arachnoid band within an epidermoid cyst: illustrative case

Jacob Kosarchuk Department of Neurosurgery, Tufts Medical Center, Tufts University School of Medicine, Boston, Massachusetts

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Shrey Patel Department of Neurosurgery, Tufts Medical Center, Tufts University School of Medicine, Boston, Massachusetts

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Walter Dent Department of Neurosurgery, Tufts Medical Center, Tufts University School of Medicine, Boston, Massachusetts

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Carl B Heilman Department of Neurosurgery, Tufts Medical Center, Tufts University School of Medicine, Boston, Massachusetts

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BACKGROUND

Intracranial epidermoid cysts (ECs) are rare benign lesions of ectodermal origin that can be found in the cerebellopontine angle (CPA). If large enough, they compress surrounding structures, causing cranial neuropathies, cerebellar dysfunction, and hydrocephalus.

OBSERVATIONS

In this case report, the authors present a patient with headaches and diplopia secondary to a CPA EC. The cyst had wrapped itself around and was strangulating the abducens nerve. This choking of the nerve was believed to have been the cause of the patient’s double vision. The arachnoid band was released with a myringotomy knife.

LESSONS

Intracranial ECs typically cause symptoms from mass effect on surrounding structures; it is unusual for one to have choked off the nerve in the fashion presented in this case. Knowledge of the potential ways that ECs can affect nervous structures is critical for resecting them without injuring normal tissue.

ABBREVIATIONS

AICA = anterior inferior cerebellar artery; CN = cranial nerve; CPA = cerebellopontine angle; EC = epidermoid cyst; MRI = magnetic resonance imaging

BACKGROUND

Intracranial epidermoid cysts (ECs) are rare benign lesions of ectodermal origin that can be found in the cerebellopontine angle (CPA). If large enough, they compress surrounding structures, causing cranial neuropathies, cerebellar dysfunction, and hydrocephalus.

OBSERVATIONS

In this case report, the authors present a patient with headaches and diplopia secondary to a CPA EC. The cyst had wrapped itself around and was strangulating the abducens nerve. This choking of the nerve was believed to have been the cause of the patient’s double vision. The arachnoid band was released with a myringotomy knife.

LESSONS

Intracranial ECs typically cause symptoms from mass effect on surrounding structures; it is unusual for one to have choked off the nerve in the fashion presented in this case. Knowledge of the potential ways that ECs can affect nervous structures is critical for resecting them without injuring normal tissue.

ABBREVIATIONS

AICA = anterior inferior cerebellar artery; CN = cranial nerve; CPA = cerebellopontine angle; EC = epidermoid cyst; MRI = magnetic resonance imaging

Intracranial epidermoid cysts (ECs) arise from ectodermal cells that become aberrantly trapped within the central nervous system during development.1 They comprise approximately 1% of all intracranial cysts.2 ECs are characterized by a thin epithelialized capsule and grow through the process of desquamation.3 An estimated 5% to 7% of ECs are found in the cerebellopontine angle (CPA).4 Although ECs are generally considered benign, their growth can exert pressure on nearby structures, leading to compression and subsequent dysfunction.5 Symptomatology is dependent on the location of the lesion; in the CPA, ECs usually result in cranial neuropathies, loss of coordination, or impairment of brainstem function.6 Radiologically, ECs typically appear hypointense on T1-weighted magnetic resonance imaging (MRI), hyperintense on T2-weighted MRI, and avidly diffusion restricted on diffusion-weighted imaging.7

The unique anatomical characteristics of ECs pose challenges for their surgical treatment.5 These tumors often exhibit tight adhesions to cranial nerves (CNs) and adjacent vascular structures, making complete resection a complex task requiring meticulous surgical technique to minimize the risk of nerve or vessel damage during cyst removal.8 Typically, ECs will encase nerves and blood vessels. Here, we present the case of a 58-year-old male presenting with an EC that had wrapped around and strangulated CN VI.

Illustrative Case

Patient Presentation

A 58-year-old male presented with horizontal diplopia and headaches. He specifically denied tinnitus, hearing loss, vertigo, facial numbness or weakness, coordination problems, dysmetria, nausea, or vomiting. On examination, he had a left CN VI palsy and imbalanced gait with heel-to-toe walking.

Preoperative Imaging

Preoperative MRI showed a T2 hyperintense (Fig. 1), T1 hypointense (Fig. 2), nonenhancing (Fig. 3) lesion in the left CPA compressing the brainstem and cerebellum medially and abutting the basilar artery. The lesion exhibited intense diffusion restriction (Fig. 4), consistent with an EC.

FIG. 1
FIG. 1

Preoperative T2 fat-suppressed MRI showing a lesion in the CPA.

FIG. 2
FIG. 2

Preoperative precontrast T1 MRI showing a lesion in the CPA.

FIG. 3
FIG. 3

Preoperative postcontrast T1 MRI showing a lesion in the CPA.

FIG. 4
FIG. 4

Preoperative diffusion-weighted T2 MRI showing a lesion in the CPA with avid diffusion restriction.

Operative Approach

The patient was placed supine with a roll under his left shoulder and his head in a Mayfield clamp and rotated to elevate the mastoid (Video 1). Facial nerve monitoring was utilized. A linear retromastoid scalp incision was made, and a left suboccipital craniotomy was performed. The dura was then opened in a curvilinear fashion.

VIDEO 1. Clip showing a left retrosigmoid craniotomy for resection of a left CPA EC. Resection of the cyst began above CN VIII, then continued below CN VIII and around the AICA and the flocculus. Once this was achieved, epidermoid material was removed off the origin of CN V and the nervus intermedius. At this point, CN VI was identified within the cyst, and a fibrous band was seen to be choking off the nerve. The band was sectioned using an apex knife and a myringotomy knife before being unwrapped from the nerve with an ear pick. Once CN VI was released, additional cyst material was removed medial to CN VI. Meckel’s cave was examined with the aid of a 30° endoscope. Once all visualized epidermoid material was removed, the wound was irrigated and closed. 2D = two dimensional; DWI = diffusion-weighted imaging; gad+ = with gadolinium. Click here to view.

After adequate exposure, the arachnoid was opened over the CPA. The epidermoid tumor was displacing CN VII and CN VIII laterally. The tumor was initially debulked above CN VIII, followed by capsular dissection and further debulking through a window between CN VIII and the lower CNs. The abducens nerve was found within the tumor, with a small fibrous band wrapped around its midportion; the proximal aspect of the nerve appeared normal, and distal to this band it was swollen and erythematous. The band was eventually released with a myringotomy knife. The cyst was then carefully dissected off the anterior inferior cerebellar artery (AICA), basilar artery, and superior cerebellar artery. After most of the epidermoid was removed, a 30° endoscope was brought in, which allowed for the identification of additional pieces of cyst within Meckel’s cave that were subsequently removed. At the end of the procedure, the facial nerve was appropriately stimulated to assess its function and integrity. The mastoid was then sealed with bone wax, and the bone flap was replaced. Pathology confirmed the diagnosis of EC.

Follow-Up Course

At 1 month, the patient had a residual left CN VI palsy requiring an eye patch and causing occasional headaches and positional dizziness, all of which resolved by the 6-month follow-up appointment. There was no facial numbness or weakness. Brain MRI performed at the 1-year follow-up showed a small focus of diffusion restriction in the left Meckel’s cave, suspicious for recurrent epidermoid (Fig. 5). The patient was neurologically intact and symptom-free at this interval; therefore, the decision was made to follow the patient clinically.

FIG. 5
FIG. 5

Postoperative diffusion-weighted MRI showing a small focus of restriction in Meckel’s cave.

Patient Informed Consent

The necessary patient informed consent was obtained in this study.

Discussion

Observations

Although encasement of the CNs and blood vessels is a common finding in intracranial ECs, to our knowledge, this is the first report of a nerve being strangulated by a small arachnoid band because of the lesion. We hypothesize that this band became wrapped around the nerve as the epidermoid grew.

Lessons

Successful release of the nerve was achieved with a myringotomy knife. Knowledge of the potential ways that ECs can affect nervous structures is critical for resecting them without injuring normal tissue.

Author Contributions

Conception and design: Heilman, Kosarchuk. Acquisition of data: Heilman, Kosarchuk, Dent. Analysis and interpretation of data: Heilman. Drafting the article: Heilman, Kosarchuk, Patel. Critically revising the article: Heilman, Kosarchuk, Patel. Reviewed submitted version of manuscript: Heilman, Kosarchuk, Patel. Approved the final version of the manuscript on behalf of all authors: Heilman. Administrative/technical/material support: all authors. Study supervision: Heilman.

Supplemental Information

Videos

Video 1. https://vimeo.com/852355839.

Previous Presentations

This work was presented as a podium presentation at the Neurosurgery at Jackson Hole Meeting held in Jackson Hole, WY, in March 2023, and as a video presentation at the North American Skull Base Society Meeting held in Tampa, FL, in February 2023.

References

  • 1

    Loy LM, Aftab S, Ang YLS, Ding SLC, Ho CL. Intracranial “white” epidermoid tumours--an imaging approach and systematic review. Clin Imaging. 2022;91:18.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 2

    Osborn AG, Preece MT. Intracranial cysts: radiologic-pathologic correlation and imaging approach. Radiology. 2006;239(3):650664.

  • 3

    Boffano P, Roccia F, Campisi P, Zavattero E, Gallesio C, Bosco GF. Epidermoid cyst of the temporal region. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2011;112(6):e113e116.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 4

    Hasegawa M, Nouri M, Nagahisa S, et al. Cerebellopontine angle epidermoid cysts: clinical presentations and surgical outcome. Neurosurg Rev. 2016;39(2):259267.

  • 5

    Epidermoid and Dermoid Cysts. Accessed May 25, 2023. https://www.neurosurgicalatlas.com/volumes/cranial-base-surgery/other-skull-base-tumors/epidermoid-and-dermoid-cysts.

    • PubMed
    • Export Citation
  • 6

    Busch CM, Prickett JT, Stein R, Cuoco JA, Marvin EA, Witcher MR. Meckel cave epidermoid cyst presenting as multiple cranial nerve deficits due to indirect tumoral compression of the cavernous sinus: a case report and literature review. World Neurosurg. 2019;121:8894.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 7

    Nagasawa D, Yew A, Safaee M, et al. Clinical characteristics and diagnostic imaging of epidermoid tumors. J Clin Neurosci. 2011;18(9):11581162.

  • 8

    deSouza CE, deSouza R, da Costa S, et al. Cerebellopontine angle epidermoid cysts: a report on 30 cases. J Neurol Neurosurg Psychiatry. 1989;52(8):986990.

  • Collapse
  • Expand
  • FIG. 1

    Preoperative T2 fat-suppressed MRI showing a lesion in the CPA.

  • FIG. 2

    Preoperative precontrast T1 MRI showing a lesion in the CPA.

  • FIG. 3

    Preoperative postcontrast T1 MRI showing a lesion in the CPA.

  • FIG. 4

    Preoperative diffusion-weighted T2 MRI showing a lesion in the CPA with avid diffusion restriction.

  • FIG. 5

    Postoperative diffusion-weighted MRI showing a small focus of restriction in Meckel’s cave.

  • 1

    Loy LM, Aftab S, Ang YLS, Ding SLC, Ho CL. Intracranial “white” epidermoid tumours--an imaging approach and systematic review. Clin Imaging. 2022;91:18.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 2

    Osborn AG, Preece MT. Intracranial cysts: radiologic-pathologic correlation and imaging approach. Radiology. 2006;239(3):650664.

  • 3

    Boffano P, Roccia F, Campisi P, Zavattero E, Gallesio C, Bosco GF. Epidermoid cyst of the temporal region. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2011;112(6):e113e116.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 4

    Hasegawa M, Nouri M, Nagahisa S, et al. Cerebellopontine angle epidermoid cysts: clinical presentations and surgical outcome. Neurosurg Rev. 2016;39(2):259267.

  • 5

    Epidermoid and Dermoid Cysts. Accessed May 25, 2023. https://www.neurosurgicalatlas.com/volumes/cranial-base-surgery/other-skull-base-tumors/epidermoid-and-dermoid-cysts.

    • PubMed
    • Export Citation
  • 6

    Busch CM, Prickett JT, Stein R, Cuoco JA, Marvin EA, Witcher MR. Meckel cave epidermoid cyst presenting as multiple cranial nerve deficits due to indirect tumoral compression of the cavernous sinus: a case report and literature review. World Neurosurg. 2019;121:8894.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 7

    Nagasawa D, Yew A, Safaee M, et al. Clinical characteristics and diagnostic imaging of epidermoid tumors. J Clin Neurosci. 2011;18(9):11581162.

  • 8

    deSouza CE, deSouza R, da Costa S, et al. Cerebellopontine angle epidermoid cysts: a report on 30 cases. J Neurol Neurosurg Psychiatry. 1989;52(8):986990.

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