Functional imaging of thymic disorders

Human thymomas are rare tumours which usually develop in the chest. The dia gnosis via guided biopsy, the evaluation of the extent of the tumour and it s boundaries with adjacent organs, the choice of the appropriate therapeuti c option, and the assessment of response to treatment are usually made with computed tomography (CT) alone or in combination with magnetic resonance i maging (MRI). More recently, radiopharmaceuticals and nuclear medicine proc edures have been used increasingly in the imaging and functional characteri zation of benign and malignant thymic disorders. Two groups of radiopharmac euticals have been used. The first includes several oncotropic tracers, suc h as Tl-201-chloride, Tc-99m-sestamibi and F-18-fluorodeoxyglucose, which a re significantly concentrated in thymic tumours. Their uptake correlates wi th tumour grades and cellularity. The second class includes two radioligand s: [In-111-DTPA-D-Phe(1)] -octreotide (DTPA, diethylenetriamine penta-aceti c acid) and [In-111-DTPA-Arg(1)]-substance P, which bind to specific recept ors. [In-111-DTPA-Arg(1)]-substance P binds to its receptors that are large ly expressed in the thymus of patients with autoimmune diseases. [In-111-DT PA-D-Phe(1)]octreotide recognizes the somatostatin receptor subtype 2, In p atients with active disease investigated in our institution [In-111-DTPA-D- Phe(1)]-octreotide has been shown to concentrate in the majority of thymoma deposits. Conversely, it is not concentrated in adult patients with benign lymphofollicular thymic hyperplasia. This finding has had a significant im pact on the management of patients with myasthenia gravis as it differentia tes early-stage thymoma from benign hyperplasia, unlike CT and MRI, which o ften fail to distinguish between the two. In addition to its role in diagno stic imaging, somatostatin receptor scintigraphy also enables us to select patients with advanced or metastatic thymoma unresponsive to conventional t herapies, who might benefit from a somatostatin analogue-based treatment, s erving thus as a link between diagnosis and therapy. In this article, we di scuss and analyse the results of functional imaging with different radiopha rmaceuticals, primarily those that we have obtained with [In-111-DTPA-D-Phe (1)] -octreotide.