Department of Nuclear Medicine, University of Health Sciences, Ankara Application and Research Hospital, Ulucanlar Street, Ankara, 06340, Turkey,

When a patient with known bone metastases underwent bone scintigraphy, it was discovered that the anterior neck region had a focally increased uptake of radioactivity compared to the patient's original scintigraphy. We'd like to demonstrate bone scintigraphy's focused uptake of a skeletal metastasis that looks like a thyroid nodule.

Keywords: Vertebral metastasis, Thyroid nodule, Bone scintigraphy

Tc-99m Osteoblastic metastases in cancer patients have been identified using Methylene Diphosphonate (MDP) bone scintigraphy, a very sensitive imaging technique [1]. However, due to pathophysiological alterations, bone scintigraphy may reveal anomalous radiotracer uptake in areas other than the skeletal system. Regarding that differential diagnosis, extra-osseous presences close to bone structures that could resemble skeletal metastatic lesions should be considered.

Due to an increase in the level of prostate-specific antigen, a 50-year-old man with prostate cancer and known bone metastases sought bone scintigraphy for reevaluation. His preoperative Tc-99m MDP bone scintigraphy 10 months prior to surgery revealed numerous areas of osteoblastic uptake that were suggestive of multiple skeletal metastases, particularly in the left iliac region. Following this, radiotherapy was administered to the left iliac region, and zoledronic acid and goserelin were given before his TUR-P procedure. With the exception of a focal increased uptake of Tc-99m-MDP prominent in the anterior neck region, which was recently observed on the recent whole-body bone scintigraphy, a significant regression in the number and intensity of the radioactivity accumulation areas was seen in the comparison with preoperative bone scintigraphy.

Oblique pictures, however, are unable to discriminate between radioactive uptake from the thyroid tissue and vertebral metastases. His TSH level was lowered by 0.01 IU/ml (reference range, 0.30 to 5.5 IU/ml) during this time. and thyroid Ultrasonography (USG) revealed a nodule in the left lobe that was 15 mm by 10 mm and had several interior calcifications, predominately microcalcifications.

However, the patient was directed to the Magnetic Resonance Imaging since the appearance did not match the uptake of the bone scintigraphy (MRI). In the left T2 vertebral corpus and T4 vertebra, MRI results showed hypo-intense sclerotic lesions without any contrast uptake. Following that, the Ga-68-PSMA PET/CT (Positron Emission Tomography/Computerized Tomography)

In general, Tc-99m MDP binds to calcium salts and hydroxyapatite crystals, causing calcium to accumulate in the skeleton and be absorbed by other tissues [2]. Hematogenous or lymphatic metastases from prostate cancer frequently extend to the bones. Bone scintigraphy, however, may show soft-tissue uptake in benign situations as well as malignant ones, such as thyroid nodules with calcification regions, tumoral calcinosis, and myositis ossificans, which may simulate metastasis due to enhanced Tc-99m MDP uptake [3,4].

It is important to consider and further assess the increased radiotracer uptake in soft tissues for the differential diagnosis. Ga-68 PSMA PET/CT and MRI in our patient revealed the differential diagnosis that the focal radioactivity accumulated in the anterior neck region during bone scintigraphy is initially the shine through of the vertebra metastasis, which is consistent with true positivity of the bone scintigraphy rather than false positivity.

1. Sood A, Sethi S, Kumar R. Tracheal uptake on Tc-99m MDP bone scintigraphy can be a potential source of false-positive results in a prostate cancer patient. Clin Nucl Med. 2010;35(6):454-5.

2. Wale DJ, Wong KK, Savas H, Kandathil A, Piert M, Brown RK. Extraosseous findings on bone scintigraphy using fusion SPECT/CT and correlative imaging. AJR Am J Roentgenol. 2015;205(1):160-72.

3. Sadic M, Akbulut A, Aydinbelge FN, Koca G, Korkmaz M. Toxic multinodular goitre identified at vascular and late phase of Tc99m MDP bone scan. Nucl Med Biomed Imaging. 2017;2(2):1-2.

4. Peller PJ, Ho VB, Kransdorf MJ. Extraosseous Tc-99m MDP uptake: A pathologic approach. Radiographics. 1993;13(4):715-34

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