Review Question - QID 219246

The patient has Acute lymphocytic leukemia (ALL), which is evident based on age, symptoms, and findings on the MRI and blood smear (Figures A and B).

Acute lymphocytic leukemia (ALL) often presents in young patients with an initial peak around the age of 4 with recurrent infections, bleeding, fatigue, and lymphadenopathy. The condition results from malignant neoplastic proliferation of lymphocytes and lymphocytic precursors and can cause symptomatic bony pain due to the presence of scattered, ill-defined osseous lesions that occur within the medullary canal of long bones. The appearance of MRI can mimic that of eosinophilic granuloma (Langerhans Cell Histiocytosis) and chronic infection (osteomyelitis). Thus, workup typically includes obtaining a peripheral blood smear and a bone marrow biopsy for confirmation. Treatment is usually chemotherapy.

Kim et al. provide a review of hematopoietic tumors and metastases involving bone. The authors note that the MR imaging appearance of leukemia is nonspecific and that it may present as diffuse infiltration without distinct lytic lesions. The signal intensity of bone on T1-weighted sequences diffusely decreases with corresponding increased signal intensity on T2-weighted sequences. This can be difficult to distinguish from Langerhans Cell Histiocytosis, in which long bone involvement is also common, resulting in typical geographic lytic lesions with little or no surrounding sclerosis that are located centrally within the intramedullary space. They conclude that these pathologic processes often have vague, nonspecific symptoms with frequently subtle imaging findings, making them a diagnostic challenge.

Arkader et al. provide an update on pediatric musculoskeletal infections. The authors note that musculoskeletal infections, including osteomyelitis, septic arthritis, and pyomyositis, are a substantial cause of morbidity in children and adolescents and are a challenge for surgeons because they mimic the presentation of other pathology, including musculoskeletal and hematopoietic tumors. Importantly, because of their small bone marrow reserve, 50% to 75% of children with acute leukemia have skeletal lesions, and 30% of children with acute leukemia have musculoskeletal symptoms that mimic infection. The authors conclude that surgeons who evaluate children with joint involvement and/or limb pain must always consider the possibility of malignancy.

Figure A is a coronal, fluid-sensitive MRI sequence of the knee demonstrating numerous well-circumscribed, high-signal intramedullary lesions of variable sizes in the periarticular femur and tibia involving both the metadiaphyses and epiphyses. Note there is minimal cortical scalloping and no overt lytic process. Figure B is a blood smear showing the presence of lymphoblasts, large round cells with coarse, clumped chromatin, inconspicuous nucleoli, and scanty cytoplasm. Illustrations A-C are labeled peripheral blood smears showing the differences between ALL, AML, and CML, respectively.

Incorrect Answers:
Answer 2: AML is most commonly seen in older adults (5th-6th decade of life), and would show myeloblasts and Auer rods on blood smear, not lymphoblasts (Illustration B).
Answer 3: CML also typically occurs in older adults (5th-6th decade), is associated with the 9;22 chromosomal translocations, and would show a peripheral blood smear with immature granulocytes, basophilia, and eosinophilia (Illustration C).
Answer 4: Leukemia can mimic chronic infection radiographically, but osteomyelitis would show a left shift with neutrophilia on blood smear, not the presence of lymphoblasts.
Answer 5: LCH (eosinophilic granuloma) can also look like leukemia on advanced imaging but is associated with eosinophilia, positive immunohistochemical staining for CD1a and CD207, and identification of Birbeck granules by electron microscopy, not with the presence of lymphoblasts.