Unusual False Positive on 99mTc-Tektrotyd Scintigraphy Mimicking Bone Metastasis

Abstract

Somatostatin receptor scintigraphy is a key diagnostic tool in the initial staging and therapeutic evaluation of neuroendocrine tumors. Its specificity can be compromised by the presence of false positives. We illustrate here the case of a vertebral hemangioma detected on ^99mTc-Tektrotyd scintigraphy as an incidental finding in a 34-year-old man referred for the staging of a well-differentiated neuroendocrine tumor of the ampulla of Vater (Fig. 1).

Keywords: Neuroendocrine tumor; Somatostatin; Somatostatin receptor; Vertebral hemangioma.

Fig. 1

We illustrate here the findings of a 34-year-old man who underwent ^99mTc-Tektrotyd scintigraphy for the staging of a well-differentiated neuroendocrine tumor (G2) of the ampulla of Vater, incidentally discovered on a cephalic duodenopancreatectomy specimen for a mass at the bilio-duodenal junction. SPECT-CT images showed an increased uptake in a hypodense lesion of the vertebral body of D7, with a polka dot appearance in the axial section (a) and thickened vertical trabeculae (c), without cortical involvement and without extension to the posterior elements (b). No pathological findings were seen elsewhere in the body. This appearance was typical of bone hemangioma. Neuroendocrine tumors (NET) are a heterogeneous group of cancers that originate from embryonic neural crest cells found in multiple organs, including the lungs, gastrointestinal tract, adrenal medulla, thyroid, and pituitary gland [1]. A common characteristic shared by these tumors is their increased expression of somatostatin receptors (SSTRs), which consist of five identified subtypes (SSTR1-SSTR5), with SSTR2 being the most prevalent in differentiated NETs [2]. ^99mTc-Tektrotyd is a radiopharmaceutical that is used for diagnosing tumors that exhibit overexpression of somatostatin receptors, primarily subtype 2 (SSTR2). It demonstrates a high binding affinity to SSTR2 and a lower binding affinity to SSTR3 and SSTR5 [3]. Occasionally, benign lesions exhibit increased uptake of ^99mTc-Tektrotyd due to elevated expression of somatostatin receptors. For example, osteoblasts express SSTR2, so degenerative bone disease, fractures, and epiphyseal growth plates in children may display increased activity on somatostatin receptor scintigraphy. In addition, false positive results can arise from the accumulation of radiolabeled somatostatin analogs in parathyroid adenomas and inflammatory processes in various organs, such as colitis, prostatitis, and thyroiditis [4]. Bone hemangioma is a vascular benign tumor that frequently appears in the spine. Its structure is composed of blood-filled vessels and sinuses within fatty marrow [5]. We present a case of somatostatin expression in vertebral hemangioma. One case of ¹¹¹In-octreotide accumulation in a subcutaneous hemangioma of a newborn has been reported in the literature [6]. Additionally, there was another case that illustrates somatostatin receptor binding in an epithelioid hemangioma [7]. ^99mTc-Tektrotyd is known to bind to endothelial cells that have been recognized to express somatostatin receptors. Binding also can occur with circulating blood cells, such as lymphocytes, monocytes, and macrophages [8]. Dotatate is also a somatostatin receptor analog. It can also accumulate in benign lesions such as inflammatory and granulomatous diseases because lymphocytes and macrophages express somatostatin receptors on their surface [9]. Two recent reports have been described about vertebral hemangioma as an incidental finding on ⁶⁸Ga-DOTATATE PET-CT [10, 11]