FDG Uptake in the Anterior Mediastinum

PII S1095-0397(99)00092-8

Clinical Positron Imaging Vol. 2, No. 6, 332. 1999 Copyright  2000 Elsevier Science Inc. Printed in the USA. All rights reserved. 1095-0397/99 $–see front matter

ABSTRACT

FDG Uptake in the Anterior Mediastinum: Physiologic Thymic Uptake or Disease? J.N. Rini, J.C. Leonidas, M.B. Tomas, G. Karayalcin, G.G. Tronco, C.J. Palestro Long Island Jewish Medical Center, Division of Nuclear Medicine, New Hyde Park, NY

The purpose of this study is to identify FDG uptake patterns that distinguish physiologic thymic activity from disease. Fourteen patients (13–23 years) underwent FDG-PET using coincidence detection. Mediastinal uptake was characterized by location and intensity (mediastinal:background ratio (M:Bkg)). In 13 patients, results were correlated with chest CT scans. Final diagnoses were Hodgkin’s disease (6), NHL (3), Ewing’s sarcoma (1), osteogenic sarcoma (1), EBV (2), and reactive lymphadenopathy (1). Thymic uptake, present in 6 patients 13–16-years-old (mean 14 years), was confined to the midline in the anterior mediastinum, was homogeneous and mild in intensity (mean M:Bkg ⫽ 2.5, range 2.2–2.7). CT scans in 5/6 patients demonstrated a triangular, convex, and prominent thymus. FDG tumor uptake, present in 4 patients 16–23-years-old (mean 19 years), generally was more posterior and eccentric in location and more intense than thymic uptake (mean M:Bkg ⫽ 3.8, range 2.7–5.5). On CT, thymus could not be differentiated due to lymphadenopathy in 3/4 patients, and in 1/4 the thymus was small. No mediastinal uptake was seen in 4 patients, age 15–22-years-old (mean 19 years). On CT, 3 had an arrowhead-shaped thymus with concave or straight borders, and 1 had a triangular-shaped thymus with a biconvex border. In the 4 FDG negative studies, the size of the thymus based on CT was considerably smaller than in the FDG positive studies. Thymic FDG uptake is seen in younger patients with larger glands. The anterior midline location and mild intensity of uptake should facilitate differentiation of thymic from tumor uptake. Results are shown in the table. (Clin Pos Imag 1999;2:332)  2000 Elsevier Science Inc. All rights reserved. Pt #

332

Age (yrs)

Diagnosis

FDG

CT findings in anterior mediastinum

M:Bkg

1

13

Pos

Thymus biconvex, triangular, large

2.3

2 *3

13 14

B-cell lymphoma Follicle center type EBV NHL

Pos Pos

2.7 2.2

4

14

Ewing’s sarcoma

Pos

5 6 7

15 15 16

NHL Osteogenic sarcoma HD MC

Neg Pos Pos

8 9 10 *11 12 13

16 17 17 20 21 22

HD NS HD NS Lymphadenopathy reactive HD NS HD NS EBV

Dz Dz Neg Neg Dz Neg

14

23

HD NS

Dz

Thymus triangular, convex on left Thymus triangular, biconvex, prominent Thymus triangular, straight, prominent Thymus Arrowhead, Straight, small CT not done Thymus biconvex, triangular, prominent Dz Dz Thymus triangular biconvex, mod size Thymus arrowhead, straight, small Dz Thymus arrowhead, right lobe only, concave, small Dz. Thymus triangular, straight, small

2.4 NA 2.6 2.5 5.5 3.0 NA NA 3.8 NA 2.7