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Case Reports
. 2025 Jun 20;17(6):e86466.
doi: 10.7759/cureus.86466. eCollection 2025 Jun.

Cerebellopontine Angle Epidermoid Cyst With Malignant Transformation Into Squamous Cell Carcinoma: An Unusual Complication of a Benign Intracranial Tumor

Dianela Gasca Saldaña  1 , Ytel Jazmin Garcilazo Reyes  2   3   4 , José Omar Navarro  3   5 , Daniel Magos Rodríguez  3 , Luis Felipe Arias Ruiz  6 , Maria Lizeth Perez Diaz  6 , Erick Gomez-Apo  7 , Raymundo Hernandez Montes de Oca  3 , Guillermo Axayacalt Gutierrez-Aceves  8   2 , Ildefonso R De La Peña  9 , Andrés Vega-Rosas  10
Affiliations
Case Reports

Cerebellopontine Angle Epidermoid Cyst With Malignant Transformation Into Squamous Cell Carcinoma: An Unusual Complication of a Benign Intracranial Tumor

Dianela Gasca Saldaña et al. Cureus. .

Abstract

Epidermoid cysts (ECs) are typically located in the posterior cranial fossa, most commonly at the cerebellopontine angle (CPA). Although generally benign, the cyst's epithelial lining can undergo malignant transformation into squamous cell carcinoma (SCC), a rare occurrence associated with poor prognosis. We present the case of a 55-year-old woman with a history of migraines who was incidentally diagnosed with a right CPA lesion consistent with an EC at the age of 30. Twenty-five years later, she developed progressive right-sided hearing loss, tinnitus, vertigo, headache, dysgeusia, and gait disturbances. Histopathological examination confirmed malignant transformation of the EC into SCC, supported by immunohistochemical markers including p63, p40, CK5/6, and D2-40. She was treated with fractionated stereotactic radiotherapy, carboplatin-paclitaxel chemotherapy, and the immune checkpoint inhibitor pembrolizumab, demonstrating good treatment tolerance and clinical stability.

Keywords: benign lesion; epidermoid cyst; intracranial tumor; malignant transformation; squamous cell carcinoma.

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Conflict of interest statement

Human subjects: Informed consent for treatment and open access publication was obtained or waived by all participants in this study. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.

Figures

Figure 1
Figure 1. Histopathological features of the tumor
Sections stained with H&E reveal a cystic cavity lined by stratified epithelial cells, with malignant cells (CA) infiltrating the underlying parenchyma (A). Both EC cells and SCC cells show positive immunoreactivity for CK5/6 (B), p40 (C), and p63 (D). Ki-67 (MIB1) staining demonstrates nuclear positivity in 20% of SCC cells (E). PD-L1 expression is observed in some malignant cells as well as in peritumoral inflammatory cells (F). EC, epidermoid cyst; SCC, squamous cell carcinoma
Figure 2
Figure 2. MRI and PET imaging
(A, B) Initial MRI T2-weighted and DWI sequences (March 2023) revealed a right CPA lesion with heterogeneous enhancement, increased size, and extension into the internal auditory canal. (C, D) Contrast-enhanced MRI and ¹⁸F-FDG brain PET demonstrated focal hypermetabolism in the right CPA region, with a maximum standardized uptake value of 10.3. CPA, cerebellopontine angle; DWI, diffusion-weighted imaging
Figure 3
Figure 3. Three-dimensional dose distribution of fractionated stereotactic radiotherapy
Axial, sagittal, and coronal sections show the target volume (tumor) in pink, surrounded by isodose lines representing various radiation dose levels, according to the color scale in gray (Gy). These images illustrate target coverage, treatment conformality, and dose distribution relative to adjacent anatomical structures. The treatment plan is designed to maximize tumor dose while minimizing exposure to surrounding healthy tissue.
See this image and copyright information in PMC

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