Diffusion Analysis of Intracranial Epidermoid, Head and Neck Epidermal Inclusion Cyst, and Temporal Bone Cholesteatoma.

Background and purpose: Intracranial epidermoid tumors, temporal bone cholesteatomas, and head and neck epidermoid inclusion cysts are typically slow-growing, benign conditions arising from ectodermal tissue. They exhibit increased signal on 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 aimed to quantitatively evaluate the ADC values and histogram features of these lesions.

Materials and methods: This retrospective study included children with histologically confirmed diagnoses of intracranial epidermoid tumors, temporal bone cholesteatomas, or head and neck epidermoid inclusion cysts. Lesions were segmented, and voxelwise calculation of ADC values was performed along with histogram analysis. ADC calculations were validated with a second analysis software to ensure accuracy. Normal brain ROIs-including the cerebellum, white matter, and thalamus-served as normal comparators. Correlational analysis and Bland-Altman plots assessed agreement among software tools for ADC calculations. Differences in the distribution of values between the lesions and normal brain tissues were assessed using the Wilcoxon rank sum and Kruskal-Wallis tests.

Results: Forty-eight pathology-proved cases were included in this study. Among them, 13 (27.1%) patients had intracranial epidermoid tumors, 14 (29.2%) had head and neck epidermoid inclusion cysts, and 21 (43.7%) had temporal bone cholesteatomas. The mean age was 8.67 (SD, 5.30) years, and 27 (52.9%) were female. The intraclass correlation for absolute agreement for lesional ADC between the 2 software tools was 0.997 (95% CI, 0.995-0.998). The intracranial epidermoid tumor, head and neck epidermoid inclusion cyst, and temporal bone cholesteatoma median ADC values were not significantly different (973.7 versus 875.7 versus 933.2 ×10^-6 mm²/s, P = .265). However, the ADCs of the 3 types of lesions were higher than those of 3 normal brain tissue types (933 versus 766, × 10^-6 mm²/s, P < .0001).

Conclusions: The ADC values of intracranial epidermoid tumors, temporal bone cholesteatomas, and head and neck epidermoid inclusion cysts 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 with the brain is likely attributable to a relatively higher contribution of the T2 shinethrough effect.