A mini-review on aplastic anemia, illustrated by a case report on bone marrow hot pockets mimicking sclerotic bone metastases.

A 61-year-old female presented with pancytopenia with a hemoglobin of 7.6 g/dL, platelet count of 26.000/µL and neutrophil count of 525/µL. Bone marrow aspirate showed moderately cellular marrow with a dysplastic erythroid lineage and poor megakaryo- and granulopoiesis without excessive blast count. Trephine biopsy revealed profoundly hypocellular marrow with rare hematopoietic elements. Conventional karyotyping was normal and next generation sequencing revealed no mutations. These findings were compatible with transfusion dependent, non-severe aplastic anaemia (AA) with grade 3 thrombopenia and neutropenia. However, diagnostic workup including CT thorax revealed unexpected sclerotic bone conversions in the spine. Additional whole body SPECT with 99mTc-HDP showed multiple bone lesions in the cervical, thoracic and lumbar spine. CT guided biopsy of D12 surprisingly revealed normal trilineage hematopoiesis. These results were very discrepant from the profoundly hypocellular marrow from the trephine biopsy. It is known that in AA residual hyperactive foci of hematopoiesis can persist; so called 'hot pockets'. MRI is the preferred imaging technique in AA; in most cases a homogeneous fatty bone marrow is found, though some patients present with a heterogeneous marrow with foci of decreased intensity, corresponding with residual foci of hematopoiesis. Imaging studies with PET-CT and PET-MRI confirm these different patterns with respectively homogeneous hypometabolism and hypometabolism with focal hyperproliferation. However, there is no previous literature on the aspect of this focal hematopoiesis on computed tomography. This is the first description of a 'hot pocket' manifesting as a sclerotic bone lesion on CT.