Figure 1
Teaching Case
SectionMusculoskeletal system
Case TypeClinical Cases
AuthorsMenon NJ, Scarsbrook AF, Chowdhury FU
Connected authors
61 years, male
A 61-year-old male patient, previously treated for medullary thyroid carcinoma, presented with rising tumour markers.
Benign bone uptake from an iliac bone graft harvest site.
Osseous metastasis
Infection
Bone scintigraphy revealed a solitary focus of avid tracer uptake in the mid-lumbar spine suggestive of an osseous metastasis (Figure 1). Subsequent MRI confirmed a solitary vertebral metastasis within the spinous process of the L3 vertebra (Figure 2), which was treated with laminectomy and spinal fusion. 3 months later recurrence was suspected with further rise in tumour markers. FDG PET-CT revealed a large osteolytic lesion within the right iliac wing (Figure 3) which could have been misinterpreted as another osseous metastasis. However, the well defined margins of the lesion suggested a surgical rather than pathological process and correlation with the prior surgical procedure revealed that this represented benign bone uptake from an iliac bone graft harvesting site. Subsequent liver MRI (Figure 4) showed a solitary lesion in segment 7 showing mild peripheral enhancement and restrictive diffusion consistent with an hepatic metastasis. This was the cause of the raised tumour markers.
Medullary thyroid cancer (MTC) is a rare tumour, arising from the para-follicular C-cells of the thyroid in sporadic or inherited form, associated with multiple endocrine neoplasia (MEN) type 2. As demonstrated in this case, imaging of patients with MTC often requires a multimodal approach [1]. Rising tumour markers (calcitonin and CEA), particularly with a rapid doubling time, have been shown to be efficient predictors of disease progression [2].
FDG PET/CT is emerging as a valuable tool in the diagnosis and staging of recurrent and metastatic medullary thyroid carcinoma, proving particularly helpful when tumour markers are elevated and conventional imaging is either negative or inconclusive [3-6]. The sensitivity of FDG PET for detecting residual, recurrent or metastatic MTC has been shown to be 62-78%, depending on the serum calcitonin level [7], and it has also been suggested that positive PET findings in this context may indicate a poor prognosis [8].
It is well recognised, however, that FDG uptake is not tumour-specific, and there are many benign processes that can cause increased FDG activity [9]. False positive bone uptake can occur in any osseous process that leads to accumulation and turnover of inflammatory cells during the healing phase, e.g. traumatic fracture and surgical resection [10,11]. The intensity and duration of activity varies with the type of surgery and the location of bone involved, with rib or vertebral uptake normalising more rapidly than those within sternum or pelvic bones [12]. Post-operative reactive bone uptake may persist for up to 4-12 months, but FDG activity persisting beyond this time should raise concern for a pathological process such as infection or malignancy [12].
This case demonstrates the characteristic metabolic and morphological features of an iliac bone graft harvest site, which is frequently employed in spinal surgery, and highlights the importance of distinguishing incidental benign bone uptake on FDG PET/CT from osseous metastasis.
FDG PET/CT is emerging as a valuable tool in the diagnosis and staging of recurrent and metastatic medullary thyroid carcinoma, proving particularly helpful when tumour markers are elevated and conventional imaging is either negative or inconclusive [3-6]. The sensitivity of FDG PET for detecting residual, recurrent or metastatic MTC has been shown to be 62-78%, depending on the serum calcitonin level [7], and it has also been suggested that positive PET findings in this context may indicate a poor prognosis [8].
It is well recognised, however, that FDG uptake is not tumour-specific, and there are many benign processes that can cause increased FDG activity [9]. False positive bone uptake can occur in any osseous process that leads to accumulation and turnover of inflammatory cells during the healing phase, e.g. traumatic fracture and surgical resection [10,11]. The intensity and duration of activity varies with the type of surgery and the location of bone involved, with rib or vertebral uptake normalising more rapidly than those within sternum or pelvic bones [12]. Post-operative reactive bone uptake may persist for up to 4-12 months, but FDG activity persisting beyond this time should raise concern for a pathological process such as infection or malignancy [12].
This case demonstrates the characteristic metabolic and morphological features of an iliac bone graft harvest site, which is frequently employed in spinal surgery, and highlights the importance of distinguishing incidental benign bone uptake on FDG PET/CT from osseous metastasis.
References
[1] Kloos RT, Eng C, Evans DB, et al (2009) Medullary thyroid cancer:management guidelines of the American Thyroid Association. Thyroid 19:565-612 (PMID: 19469690)
[2] Giraudet L, Al Ghulzan A, Auperin A, et al. (2008) Progression of medullary thyroid carcinoma: assessment with calcitonin and carcinoembryonic antigen doubling times. Eur J Endocrinol 158:239-246 (PMID: 18230832)
[3] Simon GH, Nitzsche EU, Laubenberger JJ et al. (1996) PET imaging of recurrent medullary thyroid cancer. Nuklearmedizin 35:102-104 (PMID: 8710526)
[4] Brandt-Mainz K, Muller SP, Gorges R et al (2000) The value of fluorine-18 fluorodeoxyglucose PET in patients with medullary thyroid cancer. J Nucl Med 27:490-496 (PMID: 10853802)
[5] Nanni C, Rubello D, Fanti S, et al (2006) Role of 18F-FDG PET and PET/CT imaging in thyroid cancer. Biomed Pharmacother 60:409-413 (PMID: 16891093)
[6] Zimmer LA, McCook B, Meltzer C et al (2003) Combined positron emission tomography/computed tomography imaging of recurrent thyroid cancer. Otolaryngol Head Neck Surg 128:178–184 (PMID: 12601311)
[7] Ong SC, Schoder H, Patel SG, et al (2007) Diagnostic accuracy of 18F-FDG PET in restaging patients with medullary thyroid carcinoma and elevated calcitonin levels. J Nucl Med 48:501-507 (PMID: 17401085)
[8] Bogsrud TV, Karantanis D, Nathan MA, et al (2009) The prognostic value of 2-deoxy-2-[18F]fluoro-D:-glucose positron emission tomography in patients with suspected residual or recurrent medullary thyroid. Mol Imaging Biol 2009 [Epub ahead of print] (PMID: 19949985)
[9] Rosenbaum SJ, Lind T, Antoch G, Bockisch A (2006) False-postive FDG PET uptake- the role of PET/CT. Eur Radiol 16:1054-1065 (PMID: 16365730)
[10] Shon IH, Fogelman I (2003) F-18 FDG positron emission tomography and benign fracture. Clin Nucl Med 28:171-175 (PMID: 12592121)
[11] Zhuang H, Sam JW, Chacko TK et al (2003) Rapid normalization of osseous FDG uptake following traumatic or surgical fractures. Eur J Nucl Med Mol Imaging 30:1096-1103 (PMID: 12761597)
[12] Liu Y (2009) Orthopaedic surgery-related benign uptake on FDG-PET: case examples and pitfalls. Ann Nucl Med 23:701-708 (PMID: 19728016)
Case information
| URL: | https://www.eurorad.org/case/8956 |
| DOI: | 10.1594/EURORAD/CASE.8956 |
| ISSN: | 1563-4086 |
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