What are the differential diagnoses for a patient with decreased sensorium (Glasgow Coma Scale (GCS) 12), normal electrolyte levels, and slight cerebral edema on a plain cranial Computed Tomography (CT) scan?

Differential Diagnoses for Decreased Sensorium (GCS 12) with Cerebral Edema and Normal Electrolytes

In a patient with GCS 12, normal electrolytes, and cerebral edema on CT, you must immediately consider traumatic brain injury (subdural hematoma, epidural hematoma, or diffuse axonal injury), ischemic stroke, intracranial hemorrhage, cerebral venous thrombosis, encephalitis/meningitis, and toxic/metabolic encephalopathy despite normal basic electrolytes. 1, 2

Immediate Life-Threatening Causes to Rule Out First

Traumatic Brain Injury

• Subdural hematoma is the most critical consideration in elderly patients or those on anticoagulants, as structural lesions can exist even with improving neurological status 1
• Epidural hematoma occurs in 80% of cases with skull fracture, particularly in parietal, temporal, or temporo-parietal locations 3
• Diffuse axonal injury can present with cerebral edema and altered sensorium without obvious focal lesions 3
• Even patients with GCS 13-15 can have positive CT findings requiring neurosurgical intervention in 13-40% of cases depending on initial GCS 3

Vascular Causes

• Ischemic stroke with cytotoxic edema should be considered, as cerebral edema develops from exhaustion of energy potential of cell membranes 4
• Intracerebral hemorrhage can present with surrounding vasogenic edema from increased capillary permeability to plasma proteins 4
• Cerebral venous thrombosis causes both cytotoxic and vasogenic edema with altered mental status 4

Infectious/Inflammatory Causes

• Encephalitis or meningitis produces cerebral edema through inflammatory mechanisms and increased capillary permeability 4
• Brain abscess creates vasogenic edema from breakdown of blood-brain barrier 4

Critical Metabolic/Toxic Causes Despite "Normal" Electrolytes

Hyponatremia (May Be Missed)

• Acute hyponatremia (<12 hours) causes cerebral edema with brain water content 17% above normal, leading to seizures and altered sensorium even with plasma sodium 112-119 mEq/L 5
• Chronic hyponatremia (>48 hours) can still cause symptoms with plasma sodium 115-122 mEq/L, with 12% mortality in symptomatic patients 5
• Even "mild" chronic hyponatremia causes decreased cognition and subclinical brain edema when plasma sodium is below 125 mEq/L 6, 5

Other Metabolic Causes

• Hypoglycemia can cause focal symptoms mimicking stroke with altered sensorium 3
• Hepatic encephalopathy should be considered if liver dysfunction is present 3
• Uremic encephalopathy despite "normal" basic renal function tests may require more detailed evaluation 3
• Hypoxic-ischemic encephalopathy from recent cardiac arrest or respiratory failure 4

Toxic Causes

• Drug intoxication (opioids, benzodiazepines, alcohol) can depress consciousness and may be missed without toxicology screening 3
• Carbon monoxide poisoning causes cytotoxic edema 4
• Septic encephalopathy from systemic infection 4

Algorithmic Approach to Diagnosis

Step 1: Assess for Trauma History

• If ANY history of head trauma (even minor), immediately consider subdural hematoma, epidural hematoma, or contusion 1, 2
• Look for signs of basilar skull fracture: hemotympanum, Battle's sign, periorbital ecchymosis, CSF rhinorrhea/otorrhea 2
• GCS 12-13 with trauma has 22-40% risk of positive CT findings requiring intervention 3

Step 2: Evaluate for Stroke

• Use NIH Stroke Scale to systematically assess for focal deficits suggesting vascular territory involvement 3
• Obtain immediate vascular imaging if stroke suspected, as cerebral edema indicates significant ischemic burden 3
• Check cardiac examination for arrhythmias, murmurs suggesting cardioembolic source 3

Step 3: Recheck Electrolytes More Carefully

• Verify sodium level specifically - hyponatremia is the most common electrolyte disorder causing altered mental status with cerebral edema 6, 5
• Symptomatic hyponatremia correlates with plasma sodium but has substantial overlap; patients with sodium 115-122 mEq/L can have severe symptoms 5
• Check glucose, calcium, magnesium beyond basic metabolic panel 3, 7

Step 4: Consider Infectious Causes

• Obtain lumbar puncture if meningitis/encephalitis suspected and no contraindication from mass effect 3
• Check for fever, nuchal rigidity, systemic signs of infection 3

Step 5: Toxic/Metabolic Screen

• Obtain toxicology screen, blood alcohol level as these can depress consciousness and be easily missed 3
• Check liver function tests, ammonia level, arterial blood gas if metabolic encephalopathy suspected 3

Common Pitfalls to Avoid

• Never assume GCS 12 is "mild" injury - this represents moderate traumatic brain injury requiring aggressive management and admission to monitored setting 1, 2
• Never discharge based on "normal" vital signs - vital signs do not predict intracranial injury severity 2
• Never delay CT imaging to "observe first" - imaging must be immediate with GCS ≤14 2
• Never assume normal basic electrolytes exclude metabolic causes - hyponatremia can be subtle and requires specific attention, and other metabolic derangements may need expanded testing 6, 5
• Never use long-acting sedatives or paralytics that can mask neurological deterioration during observation period 1
• Never assume improving GCS excludes structural lesions - patients can have significant intracranial injuries even with neurological improvement, especially elderly or anticoagulated patients 1

Immediate Management Priorities

• Admit to monitored setting with hourly neurological assessments (GCS, pupils, motor strength) for 24-72 hours 1
• Obtain immediate neurosurgical consultation if signs of herniation, new focal deficits, or decreasing GCS 1
• Maintain cerebral perfusion pressure >70 mmHg and normotension 1, 4
• Position head elevated 30 degrees to optimize cerebral perfusion and control intracranial pressure 4
• Perform serial CT imaging based on clinical trajectory, with repeat scans if neurological status changes 1