DOI:10.2214/AJR.04.1282
AJR 2005; 185:1057-1059
© American Roentgen Ray Society
18F-FDG Uptake in an Ovary Containing a Hemorrhagic Corpus Luteal Cyst: False-Positive PET/CT in a Patient with Cervical Carcinoma
Jennifer Ames1,
Todd Blodgett1 and
Carolyn Meltzer1,2,3
1 Department of Radiology, University of Pittsburgh Medical Center, 200 Lothrop
St., Pittsburgh, PA 15213.
2 Department of Psychiatry, University of Pittsburgh Medical Center, Pittsburgh,
PA 15213.
3 Department of Neurology, University of Pittsburgh Medical Center, Pittsburgh,
PA 15213.
Received August 14, 2004;
accepted after revision October 15, 2004.
Address correspondence to J. Ames.
Introduction
PET with 18F-FDG combined with CT (PET/CT) enables precise
localization of FDG uptake to particular structures and is useful for the
detection and staging of several malignancies
[1-3].
However, benign processes also can result in false-positive 18F-FDG
uptake [4,
5]. We report the case of a
31-year-old woman with cervical carcinoma who underwent PET/CT that showed
18F-FDG uptake in an ovary that was misinterpreted as metastatic
disease. At surgery 12 days later, the ovary contained a hemorrhagic corpus
luteal cyst that was the likely cause for the 18F-FDG
accumulation.
Case Report
A 31-year-old woman with a history of normal annual Pap smears presented
with irregular vaginal bleeding. On pelvic examination, a cervical mass was
palpable. Endocervical curettage revealed moderately differentiated invasive
squamous cell carcinoma, clinical stage IB. The patient was referred for a
staging PET/CT examination, which was performed 22 days after her last
menstrual period. Imaging was performed using a commercial PET/CT scanner that
combines a septa-less PET scanner (EXACT HR+, CPS Innovations) operated in 3D
mode only with a helical CT scanner (Somatom Emotion, Siemens Medical
Solutions). PET/CT from the neck through the pelvis was performed
approximately 1 hr after the IV injection of 8.41 mCi (311 MBq) of
18F-FDG and soon after the IV injection of 125 mL of ioversol
(Optiray 350, Mallinckrodt).
The PET/CT image at the level of the coccyx showed a large area of
increased 18F-FDG uptake corresponding to a pelvic mass and a
smaller, less intense area of increased 18F-FDG uptake
corresponding to the left ovary (Figs.
1A,
1B, and
1C). The standardized uptake
values (SUVs) of the pelvic mass and the ovary were 9.3 and 4.6, respectively.
These findings were interpreted initially as stage IV cervical carcinoma.
There were also multiple small areas of increased 18F-FDG uptake in
the chest that exhibited fatty attenuation on CT and were diminished or absent
on restaging PET/CT performed 5 months later, consistent with
18F-FDG uptake in muscle and brown fat.
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|
Fig. 1C —Ovulation in 31-year-old woman with stage IB cervical cancer.
PET/CT image at level of coccyx shows large area of increased
18F-FDG uptake corresponding to pelvic mass (long arrow).
There is smaller, less intense area of increased 18F-FDG uptake
corresponding to left ovary (short arrow). Surgical pathology
revealed normal ovary containing hemorrhagic corpus luteal cyst.
|
|
The left ovary was surgically removed 12 days after PET/CT to provide
accurate staging. Surgical pathology revealed a normal ovary containing a
hemorrhagic corpus luteal cyst without evidence of malignancy. The patient was
diagnosed with stage IB cervical carcinoma and treated with pelvic radiation.
Restaging PET/CT performed 5 months later showed no evidence of
18F-FDG uptake to suggest malignancy in the pelvis.
Discussion
PET with 18F-FDG is useful for the detection of malignancies
[1-3].
It has been used to differentiate benign from malignant lesions, to determine
the stage of malignancy, and to evaluate response to treatment regimens. In
the simplest terms, its power to discriminate malignant from normal tissue
derives from the fact that metabolism in most malignant cells is higher than
that in normal tissue. A drawback is that 18F-FDG uptake by
physiologically normal structures can lead to misdiagnosis. For example,
myocardium, thyroid, and skeletal muscle can show variable physiologic
18F-FDG uptake [4,
5]. PET/CT enables precise
localization of 18F-FDG uptake to particular structures and thus
improves differentiation of normal physiologic uptake from disease.
Physiologic 18F-FDG uptake can be challenging particularly in the
abdomen and pelvis because of multiple structures with variable physiologic
18F-FDG uptake (e.g., bowel) and because 18F-FDG is
excreted through the urinary collecting system
[4,
5].
We present a case in which 18F-FDG uptake in a normal ovary was
misinterpreted initially as a metastatic lesion. Cervical cancer stage is
determined by the amount of invasion into adjacent structures and usually is
assessed using CT or MRI. Stage I is confined to the cervix. Stage II extends
beyond the cervix but not to the pelvic sidewalls or to the lower third of the
vagina. Stage III extends to the pelvic sidewalls or lower third of the
vagina. Stage IV disease shows bladder, rectal, or distal involvement. In this
case, 18F-FDG accumulation in the ovary with an SUV of 4.6
suggested ovarian involvement by the cervical carcinoma, or stage IV
disease.
Ovarian metastases in patients with squamous cell carcinoma of the cervix
have been estimated to occur in approximately 1% of patients
[6,
7]. In truth, the ovary was not
involved and the correct stage was IB. The prognoses and treatments for these
two stages are quite different: Stage IB disease can be treated with radical
hysterectomy to preserve ovarian function in a young woman and has a cure rate
of approximately 80% [8],
whereas stage IV treatment consists of radiation therapy and adjuvant
cisplatin and has a cure rate of only 10%
[9]. Fortunately, cautious
physicians called for pathologic evidence of ovarian involvement before
assigning a definitive stage.
Change in the ovary associated with ovulation is the likely explanation for
the increased 18F-FDG accumulation in the ovary of our patient. In
support of this hypothesis, the left ovary was found to contain a hemorrhagic
corpus luteal cyst at surgery 12 days after PET/CT. Artifact due to IV
contrast administration during the CT portion of the examination was not
responsible for our findings because images without CT attenuation correction
also showed 18F-FDG uptake in the ovary
[10].
Lerman et al. [11] observed
increased 18F-FDG uptake in the ovaries of 21 of 112 premenopausal
patients without known gynecologic malignancy using PET/CT. Fifteen of these
patients were imaged near the time of ovulation as judged by the presence of
functional ovarian cysts. Our case supports the observation that events around
the time of ovulation may lead to increased 18F-FDG uptake in the
normal ovaries of premenopausal women.
In conclusion, benign ovarian 18F-FDG uptake misinterpreted as a
malignancy can have significant clinical consequences. This pitfall may be
avoided in future patients by being aware of the possibility of
18F-FDG uptake by the normal ovary, by taking the pretest
probability of malignancy into account, and possibly by performing repeat
imaging 2 weeks later at a different point in the cycle of the ovary.
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Introduction
Case Report
