British Journal of Radiology (2005) 78, 343-345
© 2005 British Institute of Radiology
doi: 10.1259/bjr/95232584
An ovary in luteal phase mimicking common iliac lymph node metastasis from a primary cutaneous peripheral primitive neuroectodermal tumour as revealed by 18-fluoro-2-deoxyglucose positron emission tomography
K-C Ho1,
K-K Ng2,
T-C Yen1 and
H-H Chou, MD3
1 Department of Nuclear Medicine, 2 Department of Radiology and 3 Division of Gynecologic Oncology, Department of Obstetrics and Gynecology, Chang Gung Memorial Hospital and University, Taoyuan, Taiwan
Correspondence: Dr Hung-Hsueh Chou, Division of Gynecologic Oncology, Department of Obstetrics and Gynecology, Chang Gung Memorial Hospital & Chang Gung University, 5 Fu-Shin Street, Kueishan, Taoyuan 333, Taiwan
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Abstract
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A 30-year-old female underwent surgical removal of a primary cutaneous peripheral primitive neuroectodermal tumour (PNET) of the left thigh. A subsequent 18-fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) scan showed abnormal accumulation of FDG in the left upper pelvic region, consistent with metastasis to a left common iliac node. A series of follow-up imaging studies revealed that a cyst of the corpus luteum of ovary was responsible for the abnormal FDG accumulation.
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Introduction
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Primary cutaneous peripheral primitive neuroectodermal tumours constitute a rare presentation of peripheral neuroectodermal tumours (PNETs), which are mainly observed in deep soft tissue. Although primary cutaneous peripheral PNET has a more favourable outcome than other forms of PNET, distant metastasis is still a major concern [1–3]. 18-fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) has proven valuable in detecting primary and local recurrent soft tissue sarcomas [4, 5]. FDG PET is therefore potentially useful for the initial staging and follow-up studies of PNET. Since lymph nodes are possible sites for distant metastases in primary cutaneous PNET [2, 3], any abnormal FDG uptake in the region of the lymph nodes should be carefully examined. We report here a false-positive FDG PET finding for a metastatic common iliac lymph node. Uptake of FDG was later found to be attributable to the luteal phase of left ovary, which was located in the left upper pelvic region. The pattern of uptake in a corpus luteum cyst using FDG PET scanning and possible causes of increased ovarian FDG uptake are discussed.
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Case report
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A 30-year-old female had a superficial, soft tissue lump in the posterior left thigh for 1 year. The raised mass was freely movable and painless. She conceived 1 month after a small mass was noted, and the mass grew slowly throughout pregnancy. An epidermal cyst was the initial diagnosis. 1 month after delivery, local excision of the mass was performed. Histopathology revealed PNET of the skin, confirmed by immunohistochemical studies. Thereafter, she underwent whole body CT, a bone scan, an MRI for the abdomen and lower limbs, and a whole body PET scan. All were negative for a malignant lesion. Owing to negative section margins and negative images results, she did not receive adjuvant chemotherapy or radiotherapy. 5 months after the initial operation, she had a whole body FDG PET scan for regular follow-up. A focal area of increased FDG uptake (maximum standard uptake value was 4.68) in the left common iliac lymph node region was revealed (Figure 1A
). A CT scan, which was performed for further confirmation, revealed an enlarged (3.7 cm) complex cystic lesion in the left external iliac region (Figure 1B). A metastatic lesion to the left common iliac lymph node could not be ruled out. Subsequent ultrasound demonstrated rich flow in the left ovary with a resistive index value lower than 0.4, indicating a hypervascular lesion, and consistent with either a tumour or a corpus luteum cyst. MRI findings were compatible with a left adnexal lesion with no evidence of intra-abdominal lymphadenopathy (Figure 1C), but an intraovary metastatic lesion could not be differentiated from a corpus luteum cyst. After reviewing the patient's menstrual history, another MRI and ultrasound were performed 2 weeks later to rule out the possibility of a false-positive finding. In the follow-up MRI, a corpus luteum cyst was found in a normal-sized left ovary (Figure 2). This dynamic change was also observed with colour Doppler flow. This patient has been followed up regularly and has remained disease-free for 18 months.
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Figure 1. (A) FDG PET scan revealed an FDG avid lesion in the left common iliac lymph node region. (B) CT scan showed a 3.7 cm complex cystic lesion in the left adnexa. (C) T2 weighted coronal MR image with fat suppression (repetition time (TR)=4000 ms, echo time (TE)=99 ms) demonstrated a comparable left adnexa lesion near the common iliac lymph node region.
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Figure 2. Follow-up T2 weighted coronal MR image with fat suppression (repetition time (TR)=5269 ms, echo time (TE)=132 ms) showed multiple small cystic changes in rosette form in the left ovary, compatible with lutein cysts.
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Discussion
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Peripheral PNET is a highly malignant neoplasm usually involving bone and/or the deeper soft tissues [6]. Rarely it occurs as a primary, superficially-based neoplasm in children and young adults [1]. Deeply located PNETs are aggressive neoplasms with a capability for widespread metastasis. Because reports concerning primitive cutaneous peripheral PNET are limited, predictions regarding the behaviour of these tumours are not easy [3]. Although cutaneous presentations of peripheral PNET may represent a clinically favourable subset of PNETs [1], distant metastases to lung, bone and lymph node have been reported [2, 3]. PNET, a soft tissue sarcoma variance, is a possible candidate for FDG PET scans [4, 5]. We used PET for initial staging and for locating possible recurrence in a patient presenting initially with a primary cutaneous peripheral primitive neuroectodermal tumour.
In this study, the follow-up FDG PET scan (5 months after wide excision treatment) demonstrated a focal increased FDG uptake near the left common iliac lymph node region, possibly located at the lymphatic drainage route of the primary tumour at the posterior aspect of the left thigh. As lymph nodes were possible metastatic sites for primary cutaneous PNET, left common iliac lymph node metastasis was suspected initially. A false-positive PET scan owing to a corpus luteum cyst was confirmed by a series of follow-up image studies.
False-positive FDG PET findings in corpus luteum cysts of the ovary have been reported previously. In a study to correlate FDG PET and histopathological findings of asymptomatic adnexal masses, one of five corpus luteum cysts (20%) showed a false-positive result [7]. False-positive FDG uptake was found in two corpus luteum cysts in another study for pre-operative assessment of asymptomatic adnexal tumours [8]. In a recent study using PET/CT to assess normal ovarian FDG uptake, increased uptake into functional ovarian cysts was observed in 15 of 21 pre-menopausal patients without known gynaecological malignancy [9]. Corpus luteum development is a complex process involving mechanisms that are similar to wound healing and tumour formation. An essential component of corpus luteum development is the recruitment of a blood supply [10]. The mechanisms associated with such development may explain how the ovary in luteal phase was considered to be a "tumour-like" mass with higher FDG uptake in PET imaging and revealed a low resistive index of ultrasound in our case.
In summary, both malignant and functional ovarian lesions can exhibit abnormal FDG uptake. Detection of a dominant functional ovarian cyst on CT and discussion of the menstrual cycle phase with patient in question should assist in differentiating physiological from malignant FDG ovarian uptake [9].
Received for publication August 16, 2004.
Accepted for publication November 25, 2004.
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References
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- Hasegawa SL, Davison JM, Rutten A, Fletcher JA, Fletcher CD. Primary cutaneous Ewing's sarcoma: immunophenotypic and molecular cytogenetic evaluation of five cases. Am J Surg Pathol 1998;22:310–8.[CrossRef][Medline]
- Chow E, Merchant TE, Pappo A, Jenkins JJ, Shah AB, Kun LE. Cutaneous and subcutaneous Ewing's sarcoma: an indolent disease. Int J Radiat Oncol Biol Phys 2000;46:433–8.[Medline]
- Banerjee SS, Agbamu DA, Eyden BP, Harris M. Clinicopathological characteristics of peripheral primitive neuroectodermal tumour of skin and subcutaneous tissue. Histopathology 1997;31:355–66.[CrossRef][Medline]
- Schwarzbach MH, Dimitrakopoulou-Strauss A, Willeke F, Hinz U, Strauss LG, Zhang YM, et al. Clinical value of [18-F] fluorodeoxyglucose positron emission tomography imaging in soft tissue sarcomas. Ann Surg 2000;231:380–6.[CrossRef][Medline]
- Lucas JD, O'Doherty MJ, Cronin BF, Marsden PK, Lodge MA, McKee PH, et al. Prospective evaluation of soft tissue masses and sarcomas using fluorodeoxyglucose positron emission tomography. Br J Surg 1999;86:550–6.[CrossRef][Medline]
- Lee CS, Southey MC, Slater H, Auldist AW, Chow CW, Venter DJ. Primary cutaneous Ewing's sarcoma/peripheral primitive neuroectodermal tumors in childhood. A molecular, cytogenetic, and immunohistochemical study. Diagn Mol Pathol 1995;4:174–81.[Medline]
- Fenchel S, Grab D, Nuessle K, Kotzerke J, Rieber A, Kreienberg R, et al. Asymptomatic adnexal masses: correlation of FDG PET and histopathologic findings. Radiology 2002;223:780–8.[Abstract/Free Full Text]
- Fenchel S, Kotzerke J, Stohr I, Grab D, Nussle K, Rieber A, et al. Preoperative assessment of asymptomatic adnexal tumors by positron emission tomography and F-18 fluorodeoxyglucose. Nuklearmedizin 1999;38:101–7.[Medline]
- Lerman H, Metser U, Grisaru D, Fishman A, Lievshitz G, Even-Sapir E. Normal and abnormal 18F-FDG endometrial and ovarian uptake in pre- and postmenopausal patients: assessment by PET/CT. J Nucl Med 2004;45:266–71.[Abstract/Free Full Text]
- Smith MF, McIntush EW, Smith GW. Mechanisms associated with corpus luteum development. J Anim Sci 1994;72:1857–72.[Abstract]
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Abstract
Introduction
