Diffusion Analysis of Intracranial and Head and Neck Epidermoid and Temporal Bone Cholesteatoma

BACKGROUND AND PURPOSE: Intracranial epidermoid tumors (IET), temporal bone cholesteatomas (TBC), and head and neck epidermoid cysts (ECs) are typically slow-growing, benign conditions arising from ectodermal tissue. They exhibit increased signal on diffusion-weighted imaging (DWI). While much of the imaging literature describes these lesions as showing diffusion restriction, we aimed to investigate these qualitative signal intensities and interpretations of restricted diffusion with respect to normal brain structures. This study aims to quantitatively evaluate the apparent diffusion coefficient (ADC) values and histogram features of these lesions.

MATERIALS AND METHODS: This retrospective study included children with histologically confirmed IET, TBC, or EC diagnoses. Lesions were segmented, and voxel-wise calculation of ADC values was performed along with histogram analysis. ADC calculations were validated with a second analysis software to ensure accuracy. Normal brain regions of interest—including the cerebellum, white matter, and thalamus—served as normal comparators. Correlational analysis and Bland-Altman plots assessed agreement between software for ADC calculations. Differences in the distribution of values between the lesions and normal brain tissues were assessed using Wilcoxon rank sum and Kruskal-Wallis tests.

RESULTS: Forty-eight pathology-proven cases were included in this study. Among them, 13(27.1%) patients had IET, 14(29.2%) had EC, and 21(43.7%) had TBC. The mean age was 8.67±5.30, and 27(52.9%) were female. The intraclass correlation for absolute agreement for lesional ADC between the two software was 0.997(95%CI=0.995-0.998). The IET, EC, and TBC median ADC values were not significantly different (973.7vs.875.7vs.933.2 x10-6 mm2/s, p=0.265). However, the ADCs of the three types of lesions were higher than those of three normal brain tissue types (933vs.766, x10-6 mm2/s, p<0.0001).

CONCLUSIONS: The ADC values of IET, TBC, and EC are higher than those of normal brain regions. It is not accurate to simply classify these lesions as exhibiting restricted diffusion or reduced diffusivity without considering the tissue used for comparison. The observed hyperintensity on DWI compared to the brain is likely attributable a relative higher contribution of T2 shine-through effect.

ABBREVIATIONS: TBC= Temporal Bone Cholesteatomas; IE= Intracranial Epidermoid; EC= Head and Neck Epidermal Inclusion cysts; DWI= Diffusion-Weighted Imaging; ADC= Apparent Diffusion Coefficient.