Nuclear Medicine

Discussion:

Hairy cell leukemia (HCL) is a low-grade B-cell lymphoma, with the following features:

• Circulating B-cells displaying cytoplasmic projections

• Splenomegaly

• Pancytopenia

• Monocytopenia

• No lymphadenopathy

 

What is the differential diagnosis of increased FDG uptake in bone marrow and the spleen?

• Hematologic Malignancies

Lymphoma (especially Hodgkin's and Non-Hodgkin's lymphoma): Both typically present with increased FDG uptake in the spleen and bone marrow, often associated with splenomegaly.

Leukemia: Chronic myeloid leukemia (CML), chronic lymphocytic leukemia (CLL), or acute leukemias can cause massive splenomegaly with increased metabolic activity in the spleen and bone marrow.

 

• Infections:

Fungal infections: Systemic fungal infections, such as histoplasmosis, can affect the spleen and bone marrow.

Viral infections: EBV (infectious mononucleosis), CMV, or HIV-related splenomegaly can present with increased FDG activity.

 

• Inflammatory and Autoimmune Conditions:

Sarcoidosis: Can present with splenic and bone marrow involvement, showing increased FDG uptake due to granulomatous inflammation.

• Extramedullary Hematopoiesis:

Seen in chronic anemias or myeloproliferative diseases like thalassemia, where the spleen and bone marrow show increased activity due to compensatory hematopoiesis.

 

 

Hematopoietic cells in the bone marrow naturally show high glycolysis, leading to 18F-FDG uptake on PET/CT. Due to this physiological background activity, recognizing distinct patterns of FDG uptake in the bone marrow is important for accurate interpretation of 18F-FDG PET/CT findings.

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FDG PET-CT findings in some of the  hemato-oncological conditions:

• Leukemia:

Diffuse FDG uptake in BM and spleen. CT shows a Hyperdense BM.

• Inflammation:

Homogeneous FDG uptake in BM and LNs. Diffuse uptake in spleen. CT is normal.

• Multiple myeloma:

Diffuse BM pattern; rarely, shift to peripheral sites. CT shows Bone fractures (if present), osteolytic bone lesions

• Hodgkin lymphoma:

Focal FDG uptake in the bones. CT shows osteolytic bone lesions and diffuse osteopenia.

• Erdheim Chester (EC):

Focal BM lesions. Extramedullary haematopoiesis (spleen, liver, central skeleton). CT shows Symmetrical cortical thickening of bone. Osteosclerosis in long bones.

• Haemophagocytic lymphocistiocytosis (HLH):

Diffuse FDG uptake in spleen and BM. CT shows Hepatosplenomegaly.

 

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References:

1. van Son, P. M., D. Evers, and E. H. J. G. Aarntzen. "The value of FDG-PET CT scans to evaluate bone marrow in haemato-oncological conditions." Neth J Med 77.7 (2019): 234-242.

2. Mayerhoefer, Marius E., et al. "MRI and PET/MRI in hematologic malignancies." Journal of Magnetic Resonance Imaging 51.5 (2020): 1325-1335.