Intradural Chordoma Mimicking an Epidermoid Cyst on Imaging

Abstract

Chordomas are rare, locally aggressive, primary bone tumors derived from primitive notochord remnants. They almost always arise within the axial skeleton, particularly in the skull base and the sacrococcygeal region. They usually present as extradural tumors, but rarely, they present as entirely intradural tumors. This report describes a case of intradural chordoma that mimicked an epidermoid cyst. A 72-year-old woman was incidentally found to have a prepontine extra-axial mass on magnetic resonance imaging. The mass gradually increased in size, and she felt discomfort in the right cheek area. The mass showed similar signal intensity to cerebrospinal fluid on T1-weighted images and T2-weighted images, but high signal intensity on fluid-attenuated inversion recovery images and diffusion-weighted images. Because the presence of very faint contrast enhancement was not noticed, the mass was preoperatively diagnosed as an epidermoid cyst. Tumor resection was performed, and the histopathological diagnosis was chondroid chordoma. Since intradural chordoma may resemble an epidermoid cyst on imaging, radiologists should check carefully for the presence of contrast enhancement and suggest the possibility of intradural chordoma.

Keywords: chordoma; epidermoid cyst; intradural chordoma; magnetic resonance imaging; mri.

Figure 1. Noncontrast-enhanced head CT of the patient.

The images show (a) axial noncontrast-enhanced CT and (b) sagittal image of the contrast-enhanced CT in the bone window. Noncontrast-enhanced head CT shows a 40-mm, well-defined, homogeneous, low-density mass in the prepontine cistern (a: arrows). The pons (P) and basilar artery (BA) are compressed dorsally by the mass. There is no obvious fat or calcification within the mass. No bone destruction of the clivus is seen (b).

Figure 2. Brain MRI of the patient.

The images show (a) axial T2-weighted image (T2WI), (b) axial T1-weighted image (T1WI), (c) axial fluid-attenuated inversion recovery (FLAIR) image, (d) axial diffusion-weighted image (DWI) (b: factor: 1000 s/mm²), (e) apparent diffusion coefficient (ADC) map, (f) axial contrast-enhanced T1WI, (g) sagittal contrast-enhanced fat-suppressed T1WI, and (h) axial reformatted image of constructive interference in steady state (CISS). The mass shows markedly high signal intensity on T2WI, similar to cerebrospinal fluid (CSF), and low signal intensity on T1WI (a, b: arrows) but mildly high signal intensity on FLAIR and DWI images (c, d: arrows). The ADC map shows lower signal intensity than CSF and higher signal intensity than brain parenchyma (e: arrow). Contrast-enhanced T1WI shows very faint honeycombed enhancement (f, g: arrows). The tumor extends into the right Meckel’s cave (h: arrowheads), and the right trigeminal nerve is compressed laterally (h: arrow).

Figure 3. Intraoperative findings of the patient.

View of the right cerebellar pontine angle observed from behind. A white, foamy tumor (T) is seen beyond the trigeminal (V), facial (VII), and auditory (VIII) nerves.

Figure 4. Histopathological findings of the tumor.

The images show (a, b) hematoxylin-eosin staining and (c) brachyury staining. Tumor cells with vacuolated or pallid cytoplasm are proliferating in irregularly shaped cord-like or foci-like fashion (a) and are accompanied by myxoid or cartilage-like stroma (b). Immunohistological findings show positive staining for brachyury stain (c). These findings are consistent with chondroid chordoma.

Figure 5. Postoperative MRI of the brain.

The images show (a) axial fluid-attenuated inversion recovery (FLAIR) image and (b) axial diffusion-weighted image (DWI) (b factor: 1000 s/mm²). A very small amount of tumor remains near the basilar artery, which shows high signal intensity on FLAIR and DWI (a, b: arrows).