Idiopathic Hypertrophic Pachymeningitis Presenting as Cavernous Sinus Syndrome Mimicking Orbital Apex Pathology: A Diagnostic Challenge.

Idiopathic hypertrophic pachymeningitis (IHP) is a rare chronic fibro-inflammatory disorder characterized by localized or diffuse thickening of the dura mater. Because its clinical and radiological manifestations overlap with infectious, autoimmune, neoplastic, and vascular disorders, diagnosis is often challenging. We report a 43-year-old woman who presented with progressive left frontotemporal headache followed by diplopia, ptosis, facial numbness, and ophthalmoplegia. Neurological examination localized the lesion to the left cavernous sinus region. Contrast-enhanced magnetic resonance imaging demonstrated enhancing dural thickening involving the left cavernous sinus and adjacent temporal dura. Extensive investigations excluded infectious, neoplastic, and autoimmune etiologies. A diagnosis of IHP was established after multidisciplinary evaluation. The patient demonstrated significant clinical improvement following corticosteroid therapy. This case highlights the importance of early magnetic resonance imaging, careful neuroanatomical localization, and systematic exclusion of secondary causes when evaluating painful cranial neuropathies.