Information on Scans

Imaging of PheoPara

When a PheoPara is suspected based on symptoms and signs, it is very important to establish a biochemical diagnosis of PheoPara first, before any (unnecessary) scanning is performed. The biochemical diagnosis of PheoPara is made by blood and urine measurements of the hormones that are produced by the tumor: catecholamines and their metabolites metanephrines. Once a biochemical diagnosis is made, the next step is imaging.

The main goal of imaging is to localize the tumor(s). There can be a single tumor or multiple ‘primary’ tumors, for example in both adrenal glands. Besides the localization of the primary tumor(s), imaging also serves to screen for metastatic lesions in for example lymph nodes, liver, bone and lungs. Treatment options such as surgery, radiation therapy, MIBG treatment and chemotherapy largely rely on the imaging findings. For example, successful surgery depends on the tumor’s exact location and association with surrounding organs. Another important goal of imaging is to confirm that tumors are in fact PheoPara rather than other types of tumors. Imaging also serves to evaluate the results of treatment, for example to see whether chemotherapy results in tumor shrinkage.

There are two types of imaging which can be used for PheoPara. The first is anatomical imaging. Anatomical imaging is performed in the radiology department. Examples of anatomical imaging techniques are ultrasound, CT (computed tomography) and MRI (magnetic resonance imaging). The second type of scanning is functional imaging, which is performed in the nuclear medicine department. Examples of functional imaging are 123I-MIBG scanning and PET (positron emission tomography). Anatomical imaging provides detailed information of the tumor’s size, shape and position, whereas functional imaging provides information, not only about the tumor’s location, but also about its functional characteristics. For example, the anatomy of a 3.5 cm adrenal tumor can be precisely delineated by CT, whereas an MIBG scan can positively identify the tumor as a Pheo, rather than another type of adrenal cancer. Functional imaging techniques can be combined with anatomical imaging during a single scanning session, for example PET-CT.

Different functional imaging techniques share the same principle. A substance, a so-called radiotracer, is injected intravenously followed by scanning using a camera. This radiotracer accumulates in the tumor(s) and has a radioactive label which makes the tumor(s) ‘light up’ on a scan. For example, accumulation of 123I-MIBG is visualized thanks to its 123-iodine radioactive label. There are several radiotracers available for PheoPara imaging. The most widely used agents are MIBG and FDG, and to a lesser extent FDOPA, FDA and octreotide. The time interval between injection of the radiotracer and scanning depends on the specific radiotracer used, varying from 1 to 48 hours. The duration of the scanning itself also varies, from one to several hours.

In order to assess the full extent of the disease and determine the tumor’s characteristics, patients with PheoPara should preferably undergo a combination of anatomical and functional imaging, for example a CT (or MRI) and a 123I-MIBG scan. In case (suspected) metastatic disease, additional FDG PET scanning should be considered, especially when there is an underlying SDHB mutation. For head and neck Para, MRI is the preferred imaging technique.

Source: Dr. H.J.L.M Timmers, Internist-Endocronologist, Radboud University-Nijmegen Medical Centre