What are the typical imagenological features of cryptococoma in immunocompromised patients, particularly those with a history of HIV/AIDS?

Imagenological Features of Cryptococcoma

Radiological Patterns Vary by Immune Status

In immunocompromised patients (particularly HIV/AIDS), cryptococcomas typically appear as nonenhancing "pseudocysts" with low signal on T1-weighted and high signal on T2-weighted MRI sequences, most commonly located in the basal ganglia, while immunocompetent hosts more frequently demonstrate small ring-enhancing lesions. 1, 2

Key Imaging Characteristics in HIV/AIDS Patients

CT Findings

• Normal CT scans occur in approximately 30% of cases (9/29 patients in one series), making CT an insensitive modality for detecting CNS cryptococcosis 3
• Cerebral atrophy is the most common finding, present in approximately 45% of cases 3
• Nonenhancing hypodense lesions are seen in only 4-5% of AIDS patients with cryptococcomas 1, 2
• Ring-enhancing lesions are uncommon in immunosuppressed hosts 1

MRI Findings (Superior to CT)

MRI identifies abnormalities in all patients with CNS cryptococcosis, even when CT appears normal 3, 4

The four distinct MRI patterns include:

1. Parenchymal cryptococcomas (30% of cases):

   • Intermediate to low signal on T1-weighted images 4
   • High signal on T2-weighted images 3, 4
   • Typically do NOT enhance after gadolinium administration 3, 4
   • Most commonly located in basal ganglia 3, 4

2. Dilated Virchow-Robin (perivascular) spaces (40-46% of cases):

   • Multiple tiny clustered foci, relatively symmetric in basal ganglia and midbrain 3, 4
   • Hyperintense on T2-weighted images 3, 4
   • Non-enhancing on post-contrast T1-weighted images 3
   • Pathologically represent spaces filled with fungi and mucoid material 3, 4

3. Miliary pattern (10% of cases):

   • Multiple small enhancing parenchymal and leptomeningeal nodules 3
   • These lesions DO enhance with gadolinium 3

4. Mixed pattern (20% of cases):

   • Combination of dilated Virchow-Robin spaces with cryptococcomas or miliary nodules 3

Size and Distribution

• Single large lesions (≥3 cm) are uncommon but clinically significant, appearing indistinguishable from pyogenic abscesses and often requiring surgical intervention 1, 2
• MRI detects masses in 21% of HIV patients with cryptococcosis 1, 2
• Multiple lesions are less common in C. neoformans (4-5%) compared to C. gattii infections (up to 30%) 1, 2

Critical Imaging Pitfalls

Enhancement Patterns

The absence of enhancement does NOT exclude cryptococcoma - in fact, nonenhancing lesions are the typical pattern in immunocompromised hosts 1, 2, 3, 4

Response to Treatment

Do not rely solely on imaging to assess treatment response - cerebral lesions can persist for prolonged periods and may paradoxically develop surrounding edema during effective antifungal therapy due to immune reconstitution inflammatory syndrome (IRIS) 2

Associated Findings

• Leptomeningeal enhancement is typically absent, even with active meningitis 3, 4
• Background white matter hyperintensity and cerebral atrophy are present in 76% of cases but reflect HIV-related changes rather than cryptococcal disease 4
• Hydrocephalus with dilated ventricles may occur and requires VP shunt placement 1, 2

Differential Diagnosis Considerations

Cryptococcomas in HIV/AIDS patients must be distinguished from:

• CNS toxoplasmosis (typically ring-enhancing with surrounding edema) 5
• Primary CNS lymphoma (usually enhancing) 5
• Tuberculomas (typically enhancing) 5
• Progressive multifocal leukoencephalopathy (white matter lesions without mass effect) 4

Tissue diagnosis via stereotactic biopsy may be necessary for large or atypical lesions, especially when CSF cultures are negative or the lesion fails to respond to antifungal therapy 1, 5, 6

Species-Specific Differences

C. gattii causes a disproportionately higher rate of cryptococcomas (up to 30% of cases) compared to C. neoformans, which partially explains the slower treatment response and need for prolonged therapy in these cases 2