British Journal of Radiology (2007) 80, 851-852
© 2007 British Institute of Radiology
doi: 10.1259/bjr/64866111
A hypermetabolic abdominal focus in a case of osteogenic sarcoma on 18FDG-PET: in vivo insight into the gravid myometrial metabolism pattern
S Basu, MBBS(Hons), DRM, DNB(Nuclear Medicine)
N Nair, MD
and
N S Baghel, MSc
Radiation Medicine Centre, Bhabha Atomic Research Centre, Tata Memorial Centre Annexe, Jerbai Wadia Road, Parel, Bombay 400 012, India
Correspondence: Dr Sandip Basu, Radiation Medicine Centre, Bhabha Atomic Research Centre, Tata Memorial Centre Annexe, Jerbai Wadia Road, Parel, Bombay 400 012, India. E-mail: drsanb{at}yahoo.com
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Introduction
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A 22-year-old primigravida presented with swelling and pain of the distal left femur and left knee region of 3
months' duration. A diagnosis of osteosarcoma (OGS) of the distal left femur was made following biopsy. She was 20 weeks pregnant at that time. She opted for medical termination of the pregnancy (MTP) at 22.5 weeks of gestation to facilitate treatment of the malignancy and underwent whole-body positron emission tomography (PET) with (18)F-fluoro-2-deoxy-D-glucose (18FDG) (Figures 1
and 2) for staging purposes 5 days after the MTP. She had no significant past medical history.
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Figure 1. Whole-body 18FDG-PET: (a) axial view; (b) coronal view; (c) sagittal view and (d) the maximum intensity projection (MIP) image.
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How would you describe the 18FDG-PET findings? What is the most likely explanation?
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Discussion
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The whole-body 18FDG-PET (Figure 1
) shows avid 18FDG uptake in the primary lesion in the left knee region and diffuse low-grade 18FDG uptake in the breasts bilaterally (noted in the maximum intensity projection (MIP) image); in addition, another reasonably sized focus can be observed over the normal urinary bladder activity (arrows). When the sagittal slices (Figure 2) are viewed, this uptake appears quite characteristic of the uptake in the entire thickness of the uterine myometrium.
Normal myometrium does not usually demonstrate 18FDG hypermetabolism. Uptake of 18FDG has been reported in benign tumours (e.g. leiomyoma) of the uterus [1, 2] and hence 18FDG-PET cannot be used to differentiate them from leiomyosarcoma. Uptake has been observed in normal endometrium in premenopausal women, mainly during the ovulatory and menstrual phases [3]. In the present case, uptake occurred throughout the thickness of the myometrium, unlike the endometrial 18FDG uptake in the midmenstrual cycle [3], which is linear and is shown by CT to correspond to the uterine endometrium.
The pattern of gravid myometrial metabolism in humans has been a subject of conjecture among embryologists and gynaecologists because of its obvious potential implications. Comparison of pregnant myometrium with striated smooth muscle such as rectus abdominis revealed a higher concentration of glucose and a higher lactate/pyruvate ratio in the pregnant myometrium but a lower concentration of triglyceride metabolites [4]. It is predicted [4] that the pregnant uterine smooth muscle utilizes glucose as the principal nutritive metabolite rather than lipids and that the anaerobic pathway of glucose metabolism is more active in the myometrium than in the striated rectus muscle. The case described here represents a relatively unusual situation in which 18FDG-PET carried out for staging purposes in a 22.5 weeks' primigravida, 5 days following therapeutic abortion, revealed uniform 18FDG uptake throughout the entire thickness of the myometrium. This reaffirms the notion that glucose is the principal fuel in pregnant myometrium and that 18FDG uptake should not be considered as disease involvement.
Uptake in the gravid uterus is an extremely unusual cause of false-positive 18FDG uptake and there have been very few reports of 18FDG-PET in pregnancy [5, 6] in which 18FDG uptake has been reported in the gestational sac, the fetal structures, placenta and the uterus. Intense 18FDG uptake is noted in the post-partum uterus [7]. Intrauterine devices also demonstrate diffuse 18FDG uptake [8]. The fetal radiation doses from 18FDG-PET are modest as recently reported: 0.017 mGy MBq–1 (about 60 mrem mCi–1) at 6–9 months' gestation; in early pregnancy, doses are about 30% higher [5]. If 18FDG-PET is clinically necessary for the management of cancer in a pregnant patient it can be performed safely after appropriate consideration of the risks and benefits. The radiation doses to the embryo/fetus can be minimized by making simple technical alterations including: (1) using a Foley's catheter to drain the radioactive urine from the urinary bladder; (2) administering reduced doses of 18FDG; (3) using conventional PET rather than PET/CT; and (4) using adequate intravenous patient hydration to help clear activity quickly.
Received for publication January 4, 2006.
Revision received January 21, 2006.
Accepted for publication March 13, 2006.
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References
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- Steingrimsdottir T, Ronquist G, Ulmsten U, Waldenstrom A. Different energy metabolite pattern between uterine smooth muscle and striated rectus muscle in term pregnant women. Eur J Obstet Gynecol Reprod Biol 1995;62:241–5.[CrossRef][Medline]
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Introduction
Discussion
