What is the clinical significance of bilateral subdural hygroma in an immunocompromised patient with suspected Cytomegalovirus (CMV) encephalitis?

Clinical Significance of Bilateral Subdural Hygroma in Suspected CMV Encephalitis

Bilateral subdural hygroma is not a recognized feature of CMV encephalitis and should prompt immediate consideration of alternative or concurrent diagnoses, particularly traumatic injury, coagulopathy, or other structural pathology unrelated to the viral infection itself.

Key Distinction: Subdural Hygroma vs. CMV-Associated Imaging Findings

The presence of bilateral subdural hygromas is not part of the characteristic imaging pattern of CMV encephalitis and represents a separate pathological process that requires independent evaluation 1, 2.

Typical CMV Encephalitis Imaging Features

CMV encephalitis in immunocompromised patients demonstrates distinct neuroimaging patterns that do not include subdural collections:

• Periventricular enhancement on CT or MRI is highly suggestive of CMV ventriculoencephalitis 1
• Subependymal gadolinium enhancement with nonspecific white matter abnormalities on T2-weighted images 1
• Progressive ventriculomegaly detected on serial CT scanning 2
• Diffuse hydrocephalus with periventricular T2 hyperintensity and leptomeningeal enhancement 3

Clinical Implications of This Discordance

The finding of bilateral subdural hygromas in your patient necessitates:

1. Reassessment of the primary diagnosis:

• Subdural hygromas typically result from trauma, coagulopathy, CSF leak, or brain atrophy—none of which are direct manifestations of CMV encephalitis 4
• Consider whether the patient has risk factors for subdural collections: falls, anticoagulation, thrombocytopenia, or prior neurosurgical procedures 4

2. Evaluation for complications of immunocompromise:

• Thrombocytopenia or coagulopathy from HIV, medications, or bone marrow suppression could predispose to subdural collections 4
• The Infectious Diseases Society of America notes that severely immunocompromised patients may have atypical imaging findings due to impaired inflammatory responses 4

3. Consideration of dual pathology:

• The subdural hygromas and CMV encephalitis may represent two separate concurrent processes requiring independent management 4
• Immunocompromised patients are at risk for multiple simultaneous CNS pathologies 4

Critical Diagnostic Pitfall

In immunocompromised patients with encephalitis, CSF may be acellular despite active CNS infection, so microbiological investigations must be performed regardless of CSF cell count 1, 4. This is particularly relevant if lumbar puncture was delayed or avoided due to concern about the subdural collections.

Proceed with CMV-Specific Workup Regardless

Despite the atypical imaging finding, complete the diagnostic evaluation for CMV:

• CSF PCR for CMV has sensitivity of 82-100% and specificity of 86-100% in immunocompromised patients 1
• Brain biopsy with viral culture remains the gold standard when definitive diagnosis is required, demonstrating characteristic "owl's eye" inclusions 1
• CSF analysis typically shows lymphocytic pleocytosis (though may be mixed or absent), low-to-normal glucose, and normal-to-elevated protein 1

Management Approach

If CMV encephalitis is confirmed:

• Treat with ganciclovir, oral valganciclovir, foscarnet, or cidofovir per guideline recommendations 1, 4
• Treatment duration should continue until immune reconstitution occurs in HIV patients (CD4 count >200 cells/μL) 1
• Patients with HIV and neurological disease should be treated in an HIV center 4

Simultaneously address the subdural hygromas:

• Neurosurgical consultation for potential drainage if causing mass effect or neurological deterioration 4
• Correct any underlying coagulopathy before invasive procedures 4
• Serial imaging to monitor for expansion, particularly if anticoagulation reversal or platelet transfusion is required 4

Bottom Line

Bilateral subdural hygromas are not a manifestation of CMV encephalitis and indicate a separate pathological process requiring independent investigation and management. Do not allow this finding to delay appropriate antiviral therapy if CMV encephalitis is otherwise suspected based on clinical presentation, immunocompromised status, and CSF/imaging findings consistent with periventricular involvement 1, 2.