SummaryReconversion of bone marrow is a reverse process of natural replacement of red marrow by yellow marrow. The occurrence of reconversion can be misleading and challenging in interpretation of musculoskeletal system imaging. Changes of signal intensity in bone marrow are frequently observed in radiological routine and its diversity can cause a suspicion of pathologic findings. Therefore, the knowledge about distribution of red and yellow bone marrow depending on age, concomitant diseases and presentation of the patient are essential for MR image interpretation.

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BK virus is one of the most common causes of hemorrhagic cystitis (HC) in children undergoing hematopoietic cell transplantation (HCT). Viruses can be found in urine and serum samples of immunocompromised patients. Malignant diseases, age, cell source, day of granulocyte reconstitution, conditioning regimen, or use of total body irradiation may play an important role in BKV epidemiology, development of hemorrhagic cystitis course, and outcome. The aim of this study was to evaluate the incidence, clinical course, and risk factors for BKV-HC in children undergoing HCT. A total number of 133 patients who were prospectively tested for BKV colonization/infection were enrolled into this multicenter analysis. Episodes of BKV-HC occurred in 36/133 (27%) enrolled subjects. In a univariate analysis for BKV-HC incidence, the following factors were significant: age >5 years, peripheral blood transplantation, matched unrelated donor (MUD) transplantation, busulfan-cyclophosphamide-melphalan conditioning regimen, and acute myeloblastic leukemia (AML) diagnosis. Presence of acute graft-versus-host disease (aGVHD) in liver and gut GVHD was a significant risk factor of BKV-HC. No BKV-attributed deaths were reported. In multivariate analysis, the incidence of HC was significantly higher in patients with AML, age >5 years, MUD transplants, and children with GVHD. HC is a frequent complication after HCT among children causes prolonged hospitalization but rarely contributes to death. We identified risk factors of BKV-HC development in children, with focus on aGVHD: we concluded that excessive immune reaction connected with GVHD and immunosuppression drugs might play a pivotal role in the development of BKV-HC.

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The aim was to evaluate the incidence, clinical course, and outcome of adenoviral infection (AdVI) in pediatric patients diagnosed and treated due to cancer and in pediatric recipients of hematopoietic stem cell. Over a 72‐month period, all‐in 5599 children with cancer: 2441 patients with hematological malignancy (HM) and 3158 with solid tumors (ST), and 971 patients after transplantation: 741 after allogeneic (allo‐HSCT) and 230 after autologous (auto‐HSCT) were enrolled into the study. Among cancer patients, 67 episodes of AdVI appeared in 63 (1.1%) children, including 45 (1.8%) with HM and 18 (0.6%; P < .001) with ST. Within transplanted patients, AdVIs were responsible for 88 episodes in 81 (8.3%) children (P < .001), including 78 (10.5%) patients after allo‐HSCT and 3 (1.3%) after auto‐HSCT. Time to develop AdVI was short, especially after allo‐HSCT. The most common clinical manifestation in cancer patients was enteritis diagnosed in 63 (94.0%) cases, while among HSCT recipient asymptomatic adenoviremia was found in 36 (40.9%) cases and the most common clinical manifestation was urinary tract infection. Cancer patients with disseminated disease, as well as HSCT recipients with either asymptomatic viremia or disseminated disease, received antiviral treatment. The most commonly used first‐line therapy was cidofovir. None of the cancer patients died due to AdVI, while within HSCT recipients three patients developed disseminated adenoviral disease and died despite antiviral treatment. In cancer patients, AdVIs are rare and associated with very good prognosis even without specific treatment. However, in allo‐HSCT recipients, disseminated disease with fatal outcome is more likely to occur.

ObjectiveThe analysis of epidemiology, risk factors and outcome of viral infections in children and adolescents after hematopoietic cell transplantation (HCT).MethodsIn this multicenter nationwide study a total of 971 HCT procedures (741 allo-HCT; 230 auto-HCT) over a period of 6 years were analyzed.ResultsDuring this period 801 episodes of viral infections were diagnosed in 442 patients. The incidence of viral infections was 57.9% in allo-HCT and 4.8% in auto-HCT patients. The most frequent infections after allo-HCT were caused by cytomegalovirus (CMV), polyoma BK virus (BKV) and Epstein–Barr virus (EBV). The majority of infections occurred within the first 4 months after allo-HCT and over 80% required pharmacotherapy or symptomatic therapy. The median time of treatment of specific viral infection ranged from 7 (for EBV) to 24 (for CMV) days. The highest mortality was observed in case of CMV infection. The risk factors for viral infections were allo-HCT, acute leukemia, acute and chronic graft versus host disease (a/cGVHD), and matched unrelated donor (MUD)/mismatched unrelated donor (MMUD)-HCT. The risk factor for death from viral infection were CMV-IgG seropositivity in acute lymphoblastic leukemia recipient, and MUD/MMUD-HCT. The incidence of EBV infection requiring pre-emptive treatment with rituximab in allo-HCT children was 19.3%. In 30.8% cases of EBV infection, these episodes were preceded by other viral infection and treated with antivirals, which did not prevent development of EBV-DNA-emia with need of rituximab treatment in 81.5% cases. In 47.7% of these cases, GVHD was a factor enabling development of significant EBV-DNA-emia during antiviral therapy of other infection.ConclusionWe have shown that antiviral drugs do not prevent EBV reactivation in allo-HCT pediatric patients.