Introduction Intracranial complications of fungal rhinosinusitis are rare but associated with significant morbidity. In immunosuppressed patients, distinguishing invasive from non-invasive disease is challenging and directly influences surgical urgency, antifungal therapy, and prognosis. Methodology A case is presented with a focused narrative review of the literature on intracranial complications of fungal rhinosinusitis, emphasising radiological features, histopathological criteria for invasion, and multidisciplinary management. Case/Results An elderly immunocompromised patient receiving immunosuppressive therapy for giant cell arteritis was found on imaging to have extensive fungal sinus disease with an associated frontal lobe abscess. The patient was clinically well without focal neurological deficit. MRI confirmed intracranial extension without features strongly suggestive of invasive fungal disease. Combined neurosurgical abscess drainage and endoscopic sinus surgery were performed. Histopathology demonstrated fungal elements without vascular invasion. The patient recovered without neurological sequelae following multidisciplinary care and targeted antimicrobial therapy. Discussion The literature indicates that intracranial complications may occur even when radiological and histological features of invasion are absent or equivocal, particularly in immunosuppressed patients. This creates diagnostic and management uncertainty when clinical, imaging, and pathological findings are discordant. Early recognition, MRI to define intracranial extent, prompt surgical source control, and coordinated multidisciplinary decision-making are critical to preventing deterioration. Conclusion Sinogenic brain abscess may complicate fungal rhinosinusitis in the absence of definitive invasive disease. In immunosuppressed patients, a high index of suspicion and timely multidisciplinary surgical intervention can achieve favourable outcomes.