Utility of single photon emission computed tomography/CT hybrid imaging over planar I-131 whole body scans in detection of adrenal metastases in differentiated thyroid cancer.

Sir,

Distant metastases to the lung and bones occur in about 10% of patients with differentiated thyroid cancer (DTC), who can still survive for many years. Other sites are less frequently seen. We report here the case of a 37 year old female who presented with multiple bilateral cervical lymphadenopathy, diagnosed as metastatic papillary thyroid cancer (PTC) on cytology. She underwent total thyroidectomy, bilateral radical neck dissection followed by radioiodine therapy. During the course of successive radioiodine therapy over six years, she developed lung and bone metastases. On the 7th post-radioiodine therapy scan, she showed a focus of radioiodine uptake in the right upper abdominal region, better seen on posterior than on anterior images. This lesion was thought to be either in the adrenals or in the ribs posteriorly [Figure 1].

Figure 1

Planar radioiodine whole body scans-anterior and posterior views showing a focus of abnormal uptake in right upper abdomen on posterior view

We did a SPECT/CT for this patient, which clearly localized the intense, focal uptake in the right adrenal gland [Figure 2]. The patient had received 1200mCi131I thus far. She was planned for another high dose therapy in view of non-availability of any other treatment in cases of disseminated thyroid cancer.

Figure 2

SPECT-CT correctly localized the uptake in the right adrenal and not the rib

Adrenal metastasis from DTC is very rare. It is generally asymptomatic and is often associated with lung or bone metastases, as in our case. Functioning adrenal metastases was first described by Koutkia and Safer. Very few cases have been reported in till now.[123] Even if the metastatic lesions concentrate radioiodine, this uptake is generally missed out because of the normal physiological uptake/excretion of radio iodine in the kidney and gut or since the lesion appears as if it is in the overlying rib.

So two important points that can be learnt from this case are: Firstly, patients with differentiated thyroid cancer may have asymptomatic involvement of the adrenal glands. Secondly SPECT/CT is very important for those lesions which are either doubtful or abnormal in location in planar whole body images.