The usefulness of SPECT/CT in lung lesion diagnosis

Objectives We assessed SPECT/CT usefulness in diagnosing lung lesions and correlated scintigraphic data with those of diagnostic CT.

Methods Ninety consecutive patients (50-84 yrs), 51 with nodules (0.9-3 cm) and 39 with masses (>3 cm) at diagnostic CT were studied. Within 1 week of CT scan, all patients underwent SPECT/CT following 740 MBq of 99mTc-tetrofosmin i.v. injection, using a rectangular dual head gamma camera integrated with a X-ray tube for low dose CT. SPECT/CT images were analysed qualitatively and correlated with diagnostic CT findings. Definitive diagnosis after scintigraphy: 70/90 patients had malignancy (60 primary carcinomas, 8 metastases, 2 recurrences) and 20/90 had benign lesions.

Results SPECT/CT was true positive in 66/70 (94.3%) patients with malignancy, detecting 30/34 (88.2%) nodules and 36/36 (100%) masses, while CT was positive in 53/70 (75.7%) patients. SPECT/CT was false negative in 4 patients, 1 with a metastasis (size: 12 mm) positive at CT and 3 with an adenocarcinoma each (size: 10-15 mm) indeterminate at CT; the latter was also indeterminate in the remaining 14 SPECT/CT positive patients, 12 with nodules (3 adenocarcinomas, 2 bronchioalveolar carcinomas, 2 carcinoids, 2 recurrences, 3 metastases) and 2 with masses (1 adenocarcinoma, 1 spinocellular carcinoma). SPECT/CT was true negative in 17/20 (85%) patients with benign lesions, while CT in 11/20 (55%); SPECT/CT was false positive, concordantly with CT, in 3 cases, 2 of whom with aspecific inflammation and 1 with Wegner’s granuloma. CT was indeterminate in the remaining 6 patients with benign lesions (2 idiopatic fibrosis, 2 chronic alveolitis, 1 antracosis, 1 hamartoma) negative at SPECT/CT.

Conclusions 99mTc-tetrofosmin SPECT/CT proved highly accurate in lung lesion diagnosis, playing an important complementary role to diagnostic CT in respect of which it showed a better performance in 22.2% of our cases. The procedure also detected carcinoids and bronchioalveolar carcinomas which can often result negative at FDG-PET. A wider SPECT/CT use is suggested in patients with lung lesions, especially with indeterminate CT