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Skull base osteomyelitis (SBO) is a rare and potentially fatal deep-space infection most commonly arising from malignant external otitis in immunocompromised or diabetic patients. Vascular complications, including septic thrombosis of the internal carotid artery (ICA) and dural venous sinuses, are among the most severe and life-threatening sequelae, yet remain underreported in the radiological literature. We present the case of a 59-year-old male with type 2 diabetes mellitus who initially presented with severe, refractory left-sided otalgia, purulent otorrhea, and progressive lower cranial nerve palsies. He was diagnosed with left-sided SBO on MRI, characterised by extensive infiltration of the carotid, lateral pharyngeal, and perivertebral spaces, with osseous involvement of the clivus, left occipital condyle, the anterior arch of C1, and the left mastoid. Critically, MRI demonstrated encasement and non-opacification of the cervical segment of the left internal carotid artery, thrombosis of the left internal jugular vein with extension to the left sigmoid sinus, and ipsilateral otomastoiditis. This case illustrates the pivotal diagnostic value of multiparametric MRI, combining fluid-attenuated inversion recovery, diffusion-weighted, and post-gadolinium sequences, in characterising the full extent of SBO and its neurovascular complications, findings that are critical for guiding urgent multidisciplinary management.