Effective localization in tumor-induced osteomalacia using 68Ga-DOTATOC-PET/CT, venous sampling and 3T-MRI

Abstract

Summary: Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by renal phosphate wasting leading to hypophosphatemia due to excessive actions of fibroblast growth factor 23 (FGF23) produced by the tumors. Although the best way of curing TIO is complete resection, it is usually difficult to detect the culprit tumors by general radiological modalities owing to the size and location of the tumors. We report a case of TIO in which the identification of the tumor by conventional imaging studies was difficult. Nonetheless, a diagnosis was made possible by effective use of multiple modalities. We initially suspected that the tumor existed in the right dorsal aspect of the scapula by ⁶⁸Ga-DOTATOC positron emission tomography/computed tomography (⁶⁸Ga-DOTATOC-PET/CT) and supported the result by systemic venous sampling (SVS). The tumor could also be visualized by 3T-magnetic resonance imaging (MRI), although it was not detected by 1.5T-MRI, and eventually be resected completely. In cases of TIO, a stepwise approach of ⁶⁸Ga-DOTATOC-PET/CT, SVS and 3T-MRI can be effective for confirmation of diagnosis.

Learning points: TIO shows impaired bone metabolism due to excessive actions of FGF23 produced by the tumor. The causative tumors are seldom detected by physical examinations and conventional radiological modalities.In TIO cases, in which the localization of the culprit tumors is difficult, ⁶⁸Ga-DOTATOC-PET/CT should be performed as a screening of localization and thereafter SVS should be conducted to support the result of the somatostatin receptor (SSTR) imaging leading to increased diagnosability.When the culprit tumors cannot be visualized by conventional imaging studies, using high-field MRI at 3T and comparing it to the opposite side are useful after the tumor site was determined.

Figure 1

Conventional imaging studies and 3T-MRI. (A) CECT undertaken as a screening for malignancy. Compared with the result of ⁶⁸Ga-DOTATOC-PET/CT (Fig. 2), the right dorsal scapula was more enhanced than the left. (B) 1.5T-MRI of the right shoulder joint. No tumors could be identified as clear lesions. (C) 3T-MRI of the right shoulder joint. It revealed a small nodule measuring 10 × 4 mm on the right dorsal scapula which is the site ⁶⁸Ga-DOTATOC uptake. (D) 3T-MRI of the left shoulder joint. No nodular lesions were detected in the left side. 251 × 213 mm (96 × 96 DPI).

Figure 2

⁶⁸Ga-DOTATOC-PET/CT. PET/CT imaging showed elevated uptake of ⁶⁸Ga-DOTATOC on the right dorsal aspect of the scapula (SUVmax: 4.9).

Figure 3

Systemic venous sampling for FGF23. Venous blood samples were collected from various veins as listed above. Each value represents FGF23 levels in these portions (pg/mL). The levels were markedly elevated in the right peripheral veins of the scapula, such as (x) and (y). (a) right external iliac vein, (b) right internal iliac vein, (c) left internal iliac vein, (d) left external iliac vein, (e) right common iliac vein, (f) left common iliac vein, (g) inferior vena cava (distal), (h) inferior vena cava (proximal), (i) superior vena cava (proximal), (j) superior vena cava (distal), (k) right brachiocephalic vein, (l) left brachiocephalic vein, (m) right brachial vein, (n) left brachial vein, (o) right internal jugular vein, (p) left internal jugular vein, (q) right external jugular vein (proximal), (r) right external jugular vein (distal), (s) left external jugular vein (proximal), (t) left external jugular vein (distal), (u) left suprascapular vein, (v) left axillary vein, (x) right suprascapular vein and (y) right axillary vein. 105 × 158 mm (96 × 96 DPI).

Figure 4

Histological analyses of the resected tumor. (A) Hematoxylin and eosin staining sections. Proliferation of spindle cells, which was consistent with PMTMCT, was seen. (B) Immunohistochemistry for SSTR2. SSTR2 staining was diffusely positive. 230 × 84 mm (96 × 96 DPI).