Allotransplantation is the process of transferring organ(s), tissue(s) or cell(s) from a healthy donor to a recipient. The two main applications of allotransplantation are solid organ transplantation and allogeneic hematopoietic stem cell transplantation. For several reasons, including the need to use immunosuppressive drugs after transplantation, recipients of allografts carry a high risk of infectious complications.

Central nervous system infections are dreadful complications of transplantation, which can be divided into brain abscesses, meningitis, and encephalitis. In particular, brain abscesses pose major diagnostic and therapeutic challenges to transplant physicians, and are frequently fatal in transplant recipients. As compared with immunocompetent patients, transplant recipients and other immunocompromised patients have an increased risk of brain abscesses due to opportunistic pathogens, including fungi, parasites, bacteria, and mycobacteria.

Determining the epidemiology of brain abscesses is critical to guide transplant teams regarding the diagnosis and management of brain abscesses in transplant recipients.

Because the incidence of brain abscesses is low after transplantation, transplant teams often have limited clinical experience in the management of these infections. Similarly, most publications focusing on post-transplant brain abscesses are either case reports, small case series, or review articles.

We therefore aim to conduct a multicentre retrospective study on the epidemiology, the characteristics, and the outcome of brain abscesses in transplant recipients in the era of new diagnostic tools and progress in prophylaxis.

Inclusion Criteria:

• Transplant recipient (i.e., solid organ transplant recipient or allogeneic hematopoietic stem cell transplant recipient)
• Radiological evidence of brain abscess(es) after transplantation
• Brain abscess(es) classified as either proven, probable or possible (see definitions below)Diagnosis of brain abscess made between January 2010 and December 2021

Exclusion Criteria:

• Opposition of the research
• Patients under guardianship

Patients with brain abscesses after transplantation