How should I evaluate and manage new‑onset visual hallucinations in a patient who suffered a motor‑vehicle‑related head injury four years ago?

Evaluation and Management of Visual Hallucinations 4 Years Post-Traumatic Brain Injury

Immediate Diagnostic Approach

Order a brain MRI without and with contrast as your primary imaging study to evaluate for delayed post-traumatic complications including chronic blood deposition, gliosis, encephalomalacia, and late-onset structural lesions such as tumors or vascular malformations. 1

MRI is superior to CT for detecting chronic traumatic sequelae that may manifest years after injury. While CT has only 30% success in detecting focal lesions, MRI with gradient echo sequences effectively identifies microhemorrhages, chronic blood deposition, gliosis, and encephalomalacia that could explain delayed neurological symptoms. 1 Contrast enhancement is warranted here because subacute or chronic lesions (including tumors or inflammatory processes) can develop years post-trauma and may enhance due to blood-brain barrier disruption. 1

Critical Differential Diagnoses to Exclude

Post-Traumatic Epilepsy

• Occipital seizures can present with elementary visual hallucinations (colored, small circular patterns flashing in temporal hemifields) lasting seconds to minutes, though some can last 20-150 minutes. 2
• Visual seizures from occipital epilepsy differ markedly from migraine aura: they involve colored circular patterns rather than achromatic zigzag lines, and typically last under 3 minutes. 2
• Order an EEG if seizures are suspected, particularly if hallucinations are stereotyped, brief, or accompanied by other ictal phenomena. 1

Late Post-Traumatic Structural Lesions

• Delayed intracranial masses (primary or metastatic tumors), vascular malformations, or chronic subdural collections can present years after trauma. 1
• Posterior circulation strokes affecting parieto-occipital regions can cause visual hallucinations even without obvious visual field defects on bedside examination. 3

Posterior Reversible Encephalopathy Syndrome (PRES)

• Though typically acute, PRES can present with formed visual hallucinations as a major manifestation, particularly in patients with blood pressure fluctuations or renal dysfunction. 4
• Check blood pressure and renal function as part of your initial workup. 4

Essential Laboratory and Clinical Workup

Perform the following tests to identify treatable secondary causes before attributing hallucinations to post-traumatic sequelae alone:

• Complete blood count, comprehensive metabolic panel, toxicology screen, urinalysis to exclude metabolic or toxic causes. 5, 6
• Medication review: Screen for anticholinergics, steroids, and dopaminergic agents that commonly cause hallucinations. 5, 6
• Formal ophthalmological examination: Vision loss occurs in 15-60% of patients with Charles Bonnet Syndrome, which requires documented visual impairment plus preserved insight that hallucinations are unreal. 5, 6
• Assess for preserved insight: If the patient recognizes hallucinations as unreal, this suggests Charles Bonnet Syndrome rather than primary psychosis or delirium. 5, 6

When to Consider Additional Advanced Imaging

If MRI is normal but clinical suspicion remains high for seizures or functional abnormalities:

• Consider functional MRI or PET as part of multimodal assessment, though these remain primarily research tools in this context. 1
• SPECT imaging may assist in prognostication for post-traumatic patients 1-2 months post-injury, but its role 4 years out is not established. 1

Management Strategy Based on Findings

If Structural Lesion Identified

• Treat the underlying pathology (tumor resection, vascular malformation management, etc.). 1
• Consider neurosurgical consultation for mass lesions or vascular abnormalities. 1

If Post-Traumatic Epilepsy Confirmed

• Initiate antiepileptic therapy with appropriate agent based on seizure semiology. 1
• Refer to epilepsy specialist for optimization of seizure control. 1

If Charles Bonnet Syndrome Diagnosed

• Educate patient and caregivers that hallucinations are benign and related to vision loss—this alone has powerful therapeutic effects. 5, 6
• Teach simple coping strategies: eye movements, changing lighting, or distraction techniques. 5, 6
• Refer for vision rehabilitation and address correctable vision loss (cataracts, refractive errors). 5, 6

If Neurodegenerative Process Suspected

• Rivastigmine is the evidence-based first choice if dementia with Lewy bodies is diagnosed, as it reduces hallucinations while improving cognition. 5, 6
• Use validated assessment tools like the Neuropsychiatric Inventory (NPI) or North-East Visual Hallucination Interview (NEVHI) to track treatment response. 5, 6

Critical Pitfalls to Avoid

• Do not assume psychiatric illness without excluding neurological and ophthalmological causes first. Premature psychiatric diagnosis is a common error. 6
• Do not rely on CT alone. CT misses 70% of focal epileptogenic lesions and is insensitive to chronic traumatic changes like gliosis and microhemorrhages. 1
• Do not overlook medication effects. Even medications started years ago can contribute to new-onset hallucinations. 5, 6
• Do not dismiss subtle posterior circulation strokes. These can present with isolated visual hallucinations without obvious focal deficits on bedside examination. 3