PET-CT in Clinical Adult Oncology: I. Hematologic Malignancies

Abstract

PET-CT is an advanced imaging modality with many oncologic applications, including staging, assessment of response to therapy, restaging and evaluation of suspected recurrence. The goal of this 6-part series of review articles is to provide practical information to providers and imaging professionals regarding the best use of PET-CT for the more common adult malignancies. In the first article of this series, hematologic malignancies are addressed. The classification of these malignancies will be outlined, with the disclaimer that the classification of lymphomas is constantly evolving. Critical applications, potential pitfalls, and nuances of PET-CT imaging in hematologic malignancies and imaging features of the major categories of these tumors are addressed. Issues of clinical importance that must be reported by the imaging professionals are outlined. The focus of this article is on [¹⁸F] fluorodeoxyglucose (FDG), rather that research tracers or those requiring a local cyclotron. This information will serve as a resource for the appropriate role and limitations of PET-CT in the clinical management of patients with hematological malignancy for health care professionals caring for adult patients with hematologic malignancies. It also serves as a practical guide for imaging providers, including radiologists, nuclear medicine physicians and their trainees.

Keywords: B-cell lymphoma; FDG; PET; T-cell lymphoma; imaging; leukemia; lymphoma; multiple myeloma; positron emission tomography.

Figure 1

Rapid effect of chemotherapy on uptake of [¹⁸F] fluordeoxyglucose (FDG) in lymphoma. (a) A pre-treatment FDG positron emission tomography-computed tomography (PET-CT) maximum intensity project (MIP) image shows marked metabolic activity in a mass in the left lower neck, left mediastinum and left upper pulmonary lobe (black arrowhead); (b) 4 days following initiation of chemotherapy, a repeat FDG PET-CT MIP image shows a marked reduction in metabolic activity in the sites of tumor involvement (black arrowhead).

Figure 2

A 60-year-old female with diffuse large B-cell lymphoma (DLBCL). (a) At presentation, [¹⁸F] fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET-CT) maximal intensity projection (MIP) image shows large hypermetabolic conglomerate abdominal nodal masses as well as left axillary nodes. Several extra-nodal sites are also seen, including bones and breasts; (b) On a MIP image after 6 cycles of chemotherapy, the same patient achieved complete metabolic response (CR); (c) MIP image after 2 years revealed relapsed disease with new lesions, including left external iliac node (black arrowhead), right proximal humerus (black arrow), linear uptake within the lower neck (black arrow); (d) Coronal fused PET-CT image, showed activity along left C7 nerve root (white arrowhead), consistent with perineural lymphomatosis which can be seen with aggressive lymphomas. White arrows show uptake in the right brain due to lymphoma involvement. Peripheral perineural spread increases the risk of central nervous system (CNS) involvement.

Figure 3

A 50-year-old-male with diagnosis of limited follicular lymphoma (FL) within an excised lymph node of the neck underwent baseline staging. (a) Axial contrast enhanced computed tomography (CT) image shows no disease in the abdomen.; (b) Axial fused [¹⁸F] fluorodeoxyglucose positron emission tomography-CT(FDG PET-CT) images, show two hypermetabolic sites of subsequently biopsy-proven FL in the left psoas muscle (white arrows). FDG PET-CT upstages disease in 19% of patients with FL, revealing occult sites not seen on other conventional imaging.

Figure 4

Three patients with mucosal associated lymphoid tissue (MALT) lymphoma. (a) [¹⁸F] fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET-CT) maximum intensity projection (MIP) image shows minimal uptake in the stomach (black arrows) in a patient with biopsy-proven MALT lymphoma of the stomach. Gastric MALT lymphoma is often associated with low/mild uptake indistinguishable from normal physiologic gastric metabolic activity; (b) Fused FDG PET/CT axial images of the head in a patient with lacrimal MALT lymphoma (white arrow); (c) Fused FDG PET-CT axial images of the neck in an additional patient show a moderately FDG-avid left parotid MALT lymphoma (white arrowhead). Unlike gastric MALT, extra-gastric MALT lymphomas are often associated with higher levels of metabolic activity on FDG PET.

Figure 5

Two adult patients with mantle cell lymphoma. (a) In an older patient, [¹⁸F] fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET-CT) MIP image shows mild uptake associated with the spleen and hypermetabolic and expanded distribution of red marrow compatible with mantle cell lymphoma, leukemic subtype; (b) In a younger patient with mantle cell lymphoma, FDG PET-CT MIP image shows diffuse adenopathy within neck, chest abdomen and pelvis, hypermetabolic splenomegaly (black arrowhead) and linear area of uptake within pelvis (black arrow) (c). Axial PET-CT in the same patient as (b) shows hypermetabolic lymphadenopathy (white arrowhead) and thickening and hypermetabolism within the distal sigmoid colon (white arrow). This was biopsy proven to be mantle cell lymphoma, classic subtype.

Figure 6

(a) A patient with Waldenstrom’s macroglobulinemia (WM) shows an expanded intertrabecular lucent marrow space (white arrowhead) on CT; (b) Axial [¹⁸F] fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET-CT) image illustrating the typical appearance of lymphoplasmacytic lymphoma (LPL) nodal disease (white arrowheads) which is often ill-defined, infiltrative-appearing, and mild-moderately hypermetabolic.

Figure 7

A patient with MM and micronodular disease. (a) [¹⁸F] fluorodeoxyglucose positron emission tomography (FDG PET) sagittal and (b) MIP images show non-specific moderate heterogeneous metabolic activity in the spine, but several focal lesions in the long bones (black arrowheads); (c,d) sagittal STIR weighted magnetic resonance imaging (MRI) of the thoracic and lumbar spine shows diffuse heterogeneous high signal intensity consistent with micronodular MM. FDG PET is less sensitive than MRI for detecting diffuse micronodular MM.

Figure 8

Aggressive myeloma with multiple extramedullary sites of tumor involvement on [¹⁸F] fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET-CT). (a) A lytic lesion of a lumbar vertebra with an epidural soft tissue component (white arrow); (b) extensive subpleural tumor (white arrowheads) as well as multiple breast tumor implants (white arrow), and (c) a large lytic lesion of the rib with a soft tissue component (white arrow).

Figure 9

Hodgkin lymphoma (HL) before and after treatment. (a) An initial staging axial chest [¹⁸F] fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET-CT) shows a hypermetabolic left anterior mediastinal mass in a young patient with HL (white arrowhead). (b) Post-treatment FDG PET-CT shows residual although smaller mass. Although metabolic activity has decrease with treatment (white arrows), there is a small focus of residual activity in a portion of the right anterior portion of the mediastinal mass concerning for persistent viable tumor. Activity within this region was significantly higher than that in the liver and the specific nodular hypermetabolic region had increased in size.

Figure 10

Two patients with peripheral T-cell lymphoma (PTCL) (a) An [¹⁸F] fluorodeoxyglucose positron emission tomography (FDG PET) maximum intensity projection (MIP) image of a patient with PTCL-NOS shows a typical pattern of multifocal disease involvement, including multiple nodal groups, the spleen (black arrowhead), and subcutaneous sites of involvement (black arrows); (b,c) Anaplastic large cell lymphoma (ALCL) demonstrates diffuse hypermetabolic dermal and subcutaneous lesions throughout the lower extremities shown on (b) FDG PET-CT MIP image (black arrow) and a (c) axial image of through the left thigh (white arrows).

Figure 11

Three patients with leukemia. (a) Acute lymphoblastic leukemia (ALL): [¹⁸F] fluorodeoxyglucose positron emission tomography (FDG PET) maximum intensity project (MIP) image shows diffuse, intense uptake within the axial and appendicular skeleton, with marked expansion into the long bones, consistent with diffuse marrow involvement of leukemia. There is also splenomegaly. ALL rarely may rarely present with solid extraosseous masses or involved nodes. (b) Chronic lymphocytic leukemia (CLL): Fused axial FDG PET-CT axial image shows mild metabolic activity in an enlarged spleen and intraabdominal lymph nodes (white arrows); (c) Richter’s syndrome (RS) transformation in CLL. There is marked metabolic activity within a retroperitoneal node and multiple splenic lesions (white arrowheads). This was biopsy-proven RS with DLBCL subtype.

Figure 12

Coexisting CLL and Richter-transformed lymph nodes (DLBCL). Pre-treatment (a,b): (a) low-level metabolic activity in multiple bilateral supraclavicular lymph nodes (CLL, white arrowhead) as well as in (b) hypermetabolic transformed left level 5nodes (DLBCL, white arrow) in the same patient; Post-treatment (c,d): Following treatment for DLBCL, the CLL nodes have responded minimally ((c), white arrowhead) but the transformed lymph nodes show metabolic resolution and marked decrease in size ((d), white arrow).