E2014. Case-Based Review of Central Nervous System Infections in the Immunocompromised
  1. Andrew Holmes; University of South Dakota Sanford School of Medicine
  2. Mark Diaz; University of South Dakota Sanford School of Medicine
  3. Anthony Kuner; University of Wisconsin School of Medicine and Public Health
  4. Megan Albertson; University of South Dakota Sanford School of Medicine
Immunocompromised patients have a unique risk for developing atypical infections in the central nervous system (CNS). Depending on the source of immunosuppression, humoral or cell-mediated lineages, patients can have greater predisposition to certain infectious pathogens (e.g., toxoplasmosis in patients with acquired immunodeficiency syndrome due to T-cell depletion). Diagnosing CNS infections requires correlation between radiologic findings, clinical history, and analysis of cerebrospinal fluid and/or tissue. Many CNS infections carry a poor prognosis if not treated in a timely manner, so it is prudent for radiologists to recognize CNS infections early and have a high level of suspicion in immunocompromised patients. Moreover, a patient may have no known disease but can present with an atypical CNS infection as their first sign of an immunocompromised state.

Educational Goals / Teaching Points
After reviewing this educational exhibit, the learner will be able to formulate a differential diagnosis for ring-enhancing lesions, discuss common CNS infections specific to immunocompromised patients, and recognize typical imaging findings of CNS infections in immunocompromised patients. This exhibit will review cases of CNS aspergillosis, cryptococcosis (with immune reconstitution inflammatory syndrome), toxoplasmosis, John Cunningham (JC) virus (progressive multifocal leukoencephalopathy), and more.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Several CNS infections (and neoplasms) can present as ring enhancing lesions, which creates a diagnostic dilemma for the radiologist. A useful acronym to remember for causes of ring-enhancing lesions is “MAGIC DR L”: metastasis, abscess, glioblastoma, infarct, contusion, demyelination, radiation necrosis, and lymphoma (particularly in the immunocompromised). Many CNS infections can present with abscess and other overlapping features including bacterial, fungal, and parasitic sources, all of which have different treatments. Some CNS infections such as JC virus do not present with ring-enhancing lesions, but rather a more nonspecific nonenhancing white matter abnormality. Other imaging techniques such as nuclear medicine imaging and magnetic resonance spectroscopy can also be used to help narrow a differential. Thallium-201 scintigraphy is classically used to differentiate between toxoplasmosis (no uptake) and lymphoma (avid uptake) in this particular patient population because both diseases can manifest as ring-enhancing lesions.

After reviewing examples of these cases, radiologists will be able to recognize characteristic imaging findings more swiftly in atypical CNS infections in their day-to-day practice which should result in improved outcomes in immunocompromised patients with CNS infections.