Subtle Enhancing Mural Thickening With Diffusion Restriction: An Early MRI Clue to Malignant Transformation in Ovarian Dermoid Cyst.

Mature cystic teratomas (MCTs) can rarely undergo malignant transformation, most frequently into squamous cell carcinoma. Preoperative diagnosis remains challenging because of the complex internal architecture of dermoid cysts, which may obscure subtle mural malignant components. We report a 46-year-old woman with bilateral ovarian teratomas, in whom malignant transformation within the left ovarian dermoid cyst was not detected on preoperative imaging and was established only on postoperative histopathology. Retrospective review of the preoperative contrast-enhanced magnetic resonance imaging (MRI) demonstrated focal irregular enhancing wall thickening with corresponding diffusion restriction along the cyst wall, correlating with the site of malignant transformation. This case highlights that even subtle enhancing mural thickening with diffusion restriction may represent early malignant transformation, warranting careful evaluation despite the absence of overt invasive features.