The imaging dynamic changes in the malignant transformation of an epidermoid cyst: a case report and literature review

Abstract

Malignant transformation of epidermoid cysts is a rare complication. Most of the previously reported cases have involved postoperative malignant transformations. We present a case of malignant transformation of a nonpostoperative epidermoid tumor into squamous cell carcinoma (SCC) that occurred in a 61-year-old Chinese woman. The patient's initial cranial MRI scan showed an epidermoid cyst with marginal enhancement in the pre-pontine cistern, and the lesion gradually enlarged after 10 months. A craniotomy was performed using to remove part of the tumor via the right retrosigmoid approach, and postoperative pathology confirmed that the transformation of the epidermoid cyst was malignant. Our case study suggests that the possibility of malignant transformation of epidermoid cyst should not be ignored on the basis of enhanced imaging features, regardless of whether they are nodular, annular, or patchy, as is the case for inflammation. Strict follow-up is required for early detection of malignant transformation to prompt correspondingly early clinical treatment.

Keywords: epidermoid cysts; follow-up; malignant transformation; pre-pontine cistern; squamous cell carcinoma.

Figure 1

MRI in December 2021. (A−E) The nodule in the pre-pontine cistern showed a low-intensity signal on T1-weighted imaging, a high-intensity signal on T2-weighted imaging, a high-intensity signal on diffusion-weighted imaging (DWI), a low-intensity signal on an apparent diffusion coefficient plot (ADC), and no enhancement on contrast-enhanced T1-weighted imaging; (F–I) the lesion is adjacent to the right edge of the pons and shows patch-like enhancement, the boundary is not clear; (C,J–L) the lesion extends from the optic chiasm to the beginning of the right abducens nerve, the lesion is in close proximity to the right trigeminal nerve, abducens nerve, and optic chiasm nerve.

Figure 2

Imaging taken in July 2022. (A) Cystic lesions are visible on the right side of the pons on T1-weighted imaging; (B−D) contrast-enhanced scan image showing that the lesion had a ring shape and nodular enhancement features, and the lesion invaded the brachium pontis and was considered to be a neoplastic lesion.

Figure 3

Imaging examination in October 2022. (A−D) A cystic solid shadow was observed in the right pons, brachium pontis, and right cerebellar hemisphere; (E) the adjacent meninges were slightly thickened; (F) speckled calcification appeared in the low-density lesion area; and (G) single-voxel 1H + MR spectroscopy (MRS).

Figure 4

Histopathology. (A) Histopathology taken from the anterior pre-pontine cistern shows lamellar keratoses with a stratified squamous epithelium lined with a sac wall, consistent with the characteristics of an epidermoid cyst (HE × 100). (B) Histopathology taken from within the brainstem shows carcinoma invasion (HE × 100). (C–F) IHC results were taken from brainstem lesions: CK (AE1/AE3) was positive (C), GATA3 (D) was positive, Vimentin was focal-expressing (E), and Ki-67 proliferation index was 20%.

Figure 5

MRI-enhanced image of postoperative lesions. (A) The image of some unresected lesions in the brainstem area before postoperative radiotherapy; (B) unresected cystic solid lesions in the brainstem on January 6, 2023; (C) the image of brainstem lesions on February 25, 2023; (D) diffuse meningeal metastases on February 25, 2023; (E) diffuse meningeal metastases on July 6, 2023; and (F) diffuse meningeal metastases on October 06, 2023.