Unusual sites of metastatic and benign I 131 uptake in patients with differentiated thyroid carcinoma

Abstract

Introduction:Differentiated thyroid carcinoma (DTC) is the most common pathological type of thyroid carcinoma, which includes papillary and follicular subtypes. DTC is usually indolent, characterized by good prognosis, and long-term survival. Total thyroidectomy is the mainstay of treatment in DTC which is followed by diagnostic whole body 131I (WBI) scan. Like other primary malignancies of the head and neck, DTC follows a consistent pattern of spread in the cervical LNs. The central compartment, level VI and VII, is the first sentinel node followed by spread to the lateral compartments levels II–V, followed by the contralateral side. Inspite of nodal involvement, DTC usually have a favourable outcome. Presence of extrapulmonary distant metastases could predict a poor prognosis for high-dose 131I therapy. However, distant metastasis occurs often as a grave event and mortality rates vary depending on metastatic sites.Aim and Objectives:A range of rare 131I concentrating DTC deposits in sella, orbit, choroid, skeletal muscles, liver, skin, costochondral soft tissue, pancreas and kidney, and a few benign 131I concentrating sites are being depicted.Materials and Methods:Metastatic sites from DTC can be easily identified by performing a whole body 131I (WBI) scan along with a stimulated thyroglobulin (Tg) estimation (TSH >30 uIU/ml). Apart from thyroid and thyroid-related diseases, certain benign non-thyroidal pathologies can concentrate radioiodine (131I). From 13,000 of our patients who underwent radioiodine scan for thyroid cancer, we have selected a few cases of 131I concentrating benign and malignant lesions for illustration.Results:Out of 13000 DTC patients who underwent whole body 131I scintigraphy in our department from Jan 2007 till Mar 2018, 25 patients revealed benign sites of 131I uptake. 61 % patients had residual thyroid tissue with or without associated nodal involvement. Remaining patients had distant metastases. Rare sites of functioning thyroid metastases and benign sites of I 131 uptake have been selected for illustration.Conclusion:Apart from the WBI (two-dimensional, planar) images, single-photon emission computed tomography-computed tomography (SPECT-CT) has been incremental in localizing benign lesions which greatly depends on their location. This pictorial review highlights the need to create an awareness to detect metastatic deposits of DTC at unexpected sites. Otherwise patients will need further investigation to rule out unsuspected sites of functioning distant metastases.

Skin metastasis as incidental finding in follicular epithelium derived – thyroid cancer

“…Follicular and papillary cancers represent differentiated thyroid malignancies, the most frequent subgroup of thyroid cancer (6,7). They are derived by follicular epithelial cells (as well as anaplastic subtype) (6,7) Their detection starts from a suspected nodule either isolated or associating multinodular goitre based on clinical and/or endocrine examination (8,9) The next logical step of evaluation is thyroid ultrasound, the best screening tool (8,9,10) ( Figure 1).…”

“…They are derived by follicular epithelial cells (as well as anaplastic subtype) (6,7) Their detection starts from a suspected nodule either isolated or associating multinodular goitre based on clinical and/or endocrine examination (8,9) The next logical step of evaluation is thyroid ultrasound, the best screening tool (8,9,10) ( Figure 1). Typical evolution of differentiated thyroid cancer is slow with a good prognosis (6,7). Thyroidectomy is the first line of approach and lifelong levothyroxine substitution is necessary in cases with total thyroid removal in association with I 131 radioiodine therapy (6,7).…”

“…Typical evolution of differentiated thyroid cancer is slow with a good prognosis (6,7). Thyroidectomy is the first line of approach and lifelong levothyroxine substitution is necessary in cases with total thyroid removal in association with I 131 radioiodine therapy (6,7). Local remnants or disease relapse as well as distant metastases usually are responsive to high dose of radioiodine therapy, re-surgery is less frequent indicated (6,7).…”

“…Local remnants or disease relapse as well as distant metastases usually are responsive to high dose of radioiodine therapy, re-surgery is less frequent indicated (6,7). The prognostic marker is blood thyroglobulin in patients who suffered a total thyroidectomy after the adjustment of its values if positive blood anti-thyroglobulin antibodies are identified (6,7). The detection of metastases associating radioiodine uptake capacity is based on whole body scintigram but the extra-thyroid I 131 uptake may also be found in so called "benign" conditions, for instance, at the level of normal liver, muscles, kidneys and even skin (6).…”

“…Hematogenous route typically involves pulmonary and osseous metastases (1,2). The local spreading involves cervical lymph nodes (6). The sentinel node is located within central compartment (levels VI and VII); the second station is lateral compartment (levels II, III, IV, and V) followed by contralateral neck region (6).…”