Utility of single photon emission tomography/computed tomography in characterizing an additional focus of iodine uptake in post-treatment whole body iodine scan.

Sir,

A 27-year-old female, a known case of follicular variant of papillary thyroid cancer (pT2, Nx, M0) was referred to nuclear medicine department after thyroidectomy. She underwent whole body iodine scanning 48 h after oral administration of 74 MBq of 131-Iodine. There was iodine avid residual thyroid tissue and cervical lymph nodal metastases in the neck. No other site of abnormal iodine avidity was noted.

Patient was treated with high dose radioiodine (100 mCi) in another center. Post-therapy scans acquired after 7 days at our center showed a focus of tracer uptake in the left side of face [Figure 1]. Hybrid single photon emission tomography/computed tomography (SPECT/CT) imaging localized the uptake to a mucosal thickening in the left maxillary sinus [Figure 1 arrow]. A detailed history from the patient revealed that the patient developed upper respiratory infection and features of left maxillary sinusitis after the high dose therapy. The accumulation in the left maxillary sinus was attributed to the sinusitis, which was also evident on SPECT/CT images.

Figure 1

Whole body images (anterior view) of pre-radioiodine therapy scan (a) Post-treatment scan (b) Along with computed tomography (CT) images of the head in coronal (c) Sagittal (d) and axial (e) Views and fused single photon emission tomography/CT images of the head in coronal (f) Sagittal (g) and axial (h) Views showing tracer accumulation in the left maxillary sinus. Also note is minimal mucosal thickening in the left maxillary sinus (arrow)

Iodine is actively taken up into the thyroid follicles by sodium iodine symporter (NIS).[1] NIS is expressed at the highest level in the thyroid and lactating breast.[2] NIS is also expressed in the salivary glands, nasal mucosa, lacrimal sac and nasolacrimal ducts.[3] The expression of NIS and the ability to trap iodine explains the retention of radioiodine in maxillary sinus in this patient with maxillary sinusitis. SPECT/CT is of benefit in variety of thyroid diseases.[4567] Although post-therapy scanning can identify new sites of metastases that were missed in pre-therapy scanning in 10-26% of the patients,[8] it must be remembered that not all new sites noted are due to metastatic disease.