Imaging of Central Nervous System Complications of Hematopoietic Stem Cell Transplant: A Chronologic Approach to Pathology and Implications for Management

Hematopoietic stem cell transplantation is used to treat a wide pathologic spectrum and is preceded by conditioning chemoradiation. The recipient's immune system changes dramatically and predictably during treatment and recovery. Immune system recovery after hematopoietic stem cell transplantation can be divided into 3 phases. During the first phase (days < 30), the patient is pancytopenic, and clinical risk is dominated by neutropenia. Prophylaxis regimens have changed the infections encountered during this period, but patients remain susceptible to invasive fungi, which must be diagnosed quickly. Besides infection, intracranial pathology during this period includes stroke, hemorrhage, medication toxicity, and metabolic disorders. The second phase (days 30‐100) occurs after engraftment. The patient is no longer neutropenic, and antiviral prophylaxis has decreased rates of cytomegalovirus, herpes simplex virus, and varicella zoster virus. However, radiologists should be aware of the distinct imaging appearances of human herpesvirus 6 and progressive multifocal leukoencephalopathy during this period because they are fatal if untreated. During the third phase (days > 100), radiologists should recognize development of late-onset cytomegalovirus, which has emerged in numerous patients after development of ganciclovir resistance, aspergillosis, treatment changes (not to be confused with pathology), and posttransplantation lymphoproliferative disorder and disease recurrence.

Learning Objective: Understand changes in patients' immune system after hematopoietic stem cell transplantation to identify potential pathogens and characteristic imaging features of disease during each phase of marrow recovery.