Differentiation of metastatic versus non-metastatic mediastinal lymph nodes in patients with non-small cell lung cancer using respiratory-triggered short inversion time inversion recovery (STIR) turbo spin-echo MR imaging

Abstract

Objectives: To differentiate between metastatic and non-metastatic lymph nodes in patients with non-small cell lung cancer using respiratory-triggered short inversion time inversion recovery (STIR) turbo spin-echo (SE) MR imaging. Methods and patients: One hundred and forty mediastinal lymph nodes were detected in 25 patients with non-small cell lung cancer who underwent respiratory-triggered STIR turbo SE imaging. Ratios of signal intensity of lymph nodes to 0.9% saline phantoms (lymph node-saline ratio) were compared by Student's t-test using the pathological diagnosis as the gold standard. The threshold value of the lymph node-saline ratio was determined for a positive test, and tested for its capability to provide a differential diagnosis. Results: One hundred and forty lymph nodes were diagnosed and classified into two groups: metastatic lymph node (n=21) and non-metastatic lymph node (n=119). The mean lymph node-saline ratio in the non-metastatic lymph node group (0.42±0.01; mean±standard error) was significantly lower than that of the metastatic lymph node group (0.77±0.02, P<0.0001). When 0.6 was adapted as the threshold for a positive test, sensitivity, specificity, and accuracy for differentiating metastatic lymph node from non-metastatic lymph node per lymph nodes were 100, 96, and 96%, and sensitivity, specificity, and accuracy for differentiating metastatic lymph node from non-metastatic lymph node per patients were 100, 75, and 88%, respectively. Conclusions: Both metastatic and non-metastatic lymph nodes in patients with non-small cell lung cancer were well differentiated using respiratory-triggered STIR turbo SE imaging.

Introduction

Accurate tumor staging is essential for choosing the appropriate treatment strategy for lung cancer patients. Surgical resection is the treatment of choice for non-small cell lung cancer. Patients with ipsilateral hilar (N1 disease) and mediastinal lymph node metastasis (N2 disease) are considered to have potentially resectable disease. If contralateral mediastinal lymph node metastases (N3 disease) are present, surgery is generally not indicated. Due to the substantial limitation of computed tomography (CT) and magnetic resonance (MR) imaging in depicting mediastinal lymph node metastases, mediastinoscopy with biopsy is necessary for adequate assessment of hilar and mediastinal nodes [1], [2], [3], [4], [5], [6], [7], [8], [9], [10].

Historically, CT and MR imaging criteria for tumor involvement have relied on lymph node size. [1], [2], [3], [4], [5], [6], [7], [8], [9], [10]. However, in some cases, a normal-sized regional lymph node may prove to have metastases by histologic examination, and nodal enlargement can be due to reactive hyperplasia or other nonmalignant conditions [1], [2], [3], [4], [5], [6], [7], [8], [9], [10].

On the other hand, promising results using positron emission tomography (PET) with 2-[fluorine-18] fluoro-2-deoxy-d-glucose (FDG) or [carbon-11]-chorine have been reported [11], [12], [13], [14]. PET imaging has been utilized to differentiate metastatic lymph nodes from non-metastatic lymph nodes based on the biochemical mechanism of increased glucose metabolism or duplication of tumor cell [11], [12], [13], [14]; however, elevated glucose metabolism may be secondary to tumor, infection or inflammation [15], [16]. Moreover, the diagnostic capability of the FDG-PET imaging is limited because standard uptake values of FDG-PET are affected by size of lymph nodes [11].

Recently, some investigators have discussed the utility of short inversion time (TI) inversion recovery (STIR) imaging for detection of metastatic tumors and metastatic lymph nodes [17], [18], [19], [20], [21], [22]. The STIR turbo spin-echo (SE) is a simple sequence which can be easily incorporated into clinical protocol. In this study, we hypothesized that respiratory-triggered STIR turbo SE imaging can be used to differentiate metastatic from non-metastatic lymph nodes in patients with non-small cell lung cancer.