A 61-year-old male patient, previously treated for medullary thyroid carcinoma, presented with rising tumour markers.
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.
Benign bone uptake from an iliac bone graft harvest site.
Based on the provided FDG PET/CT and MRI images, the following key features are observed:
Given the patient’s history of medullary thyroid carcinoma and the current imaging findings, the following possibilities should be considered:
Considering the patient’s age, history of medullary thyroid carcinoma, postoperative status, tumor marker levels, and imaging findings, the most likely diagnosis is “postoperative reactive changes at the iliac bone graft site”, rather than metastatic bone disease. If tumor markers continue to rise significantly or if clinical symptoms worsen, follow-up imaging or additional targeted evaluations may be necessary. However, current imaging findings suggest a benign healing process.
As imaging does not indicate new bone metastasis, no specific antitumor therapy for the iliac region is currently required. Future management primarily involves:
Throughout the exercise program, adherence to the FITT-VP principle (Frequency, Intensity, Time, Type, Volume, and Progression) is essential, with adjustments according to the patient’s tolerance level.
This report is based solely on the provided history and imaging findings for reference purposes and does not replace in-person consultations or professional medical advice. Actual diagnosis and treatment should be determined in conjunction with the patient’s specific circumstances and in consultation with a specialist or multidisciplinary team.
Benign bone uptake from an iliac bone graft harvest site.
