A Case Report of High 18F-FDG PET/CT Uptake in Progressive Transformation of the Germinal Centers

Abstract

Progressive transformation of the germinal centers (PTGC) is a benign reaction pattern in lymph nodes. An association with Hodgkin disease (HD) has been reported and PTGC may precede, coexist, or present after the diagnosis of HD. This case report describes a patient who presented with unprovoked pulmonary embolism and subsequent investigations showed a solitary abdominal mass, which was subsequently proven to be PTGC. PTGC is usually avid on fluorine-18-labeled fluorodeoxyglucose positron emission tomography with computed tomography for attenuation correction and may be mistaken for neoplastic disease. Being a reactive etiology, the metabolic activity is generally low with a low maximum standardized uptake value (SUVmax), but in our case, the metabolic activity and corresponding SUVmax were relatively high making the diagnosis difficult, as most clinicians would consider a high metabolically active process more likely malignant. Recognition of PTGC is important, as it is not a malignant process. Owing to its reported associations, however, patients with this diagnosis will likely require regular surveillance.

FIGURE 1

Computed tomography pulmonary angiogram shows multifocal filling defects in the pulmonary arterial system in keeping with acute bilateral pulmonary embolism.

FIGURE 2

Abdominal ultrasound scan demonstrates an ovoid homogenous hypoechoeic mass anterior to the inferior vena cava and aorta in the mid abdomen.

FIGURE 3

Abdominal computed tomography after administration of oral and intravenous iodinated contrast shows a homogenous enhancing mass in the root of the mesentry. No internal calcification or necrosis.

FIGURE 4

F-18 FDG PET/CT maximum intensity projection (A), CT for attenuation correction (B), and PET (C) images show the mass was intensely FDG avid (SUVmax 6.6). No enlarged or FDG avid lymph node was present elsewhere above or below the diaphragm. F-18 FDG PET/CT = fluorine-18-labeled fluorodeoxyglucose positron emission tomography with computed tomography for attenuation correction.

FIGURE 5

Histopathology examination shows an increased number of variably sized and significantly enlarged follicles (A). There was infiltration and accumulation of the mantle zone lymphocytes within the larger follicles on the CD79a stain (B). There was BCL2 negativity within the follicle (C). L&H cells and classical Reed-Sternberg-like cells were absent.