papillary and follicular carcinomas of the thyroid gland , commonly referred to together as differentiated thyroid carcinoma ( dtc ) , are characterized by a slowly progressive course , and a 10-year survival rate as high as 80 - 95% .
distant metastases are seen in a minority of the patients and the reported rates of occurrence range from 4% to 15% .
the most common site of distant metastases is the lung , followed by the bone .
we present a case of asymptomatic radioiodine - avid renal and brain metastases presenting 20 years after hemi - thyroidectomy for adenomatous goiter and identified with i - whole body scintigraphy ( wbs ) and i single photon emission computed tomography / computed tomography ( i - spect / ct ) .
a 65-year - old man , investigated at a different hospital for intermittent cough and white - colored expectoration for 4 months , was found to have multiple bilateral nodular lesions on a chest x - ray [ figure 1a ] and a hyperdense lesion ( arrow ) in the right posterior parietal lobe of the brain on ct [ figure 1b ] .
he had undergone left hemi - thyroidectomy 20 years previously , reportedly for adenomatous goiter .
since serum thyroglobulin ( tg ) was > 3000 ng / ml , a provisional diagnosis of metastatic dtc was made .
however , abdominal ultrasonography ( usg ) showed multiple echogenic round lesions with areas of necrosis and internal vascularity in both kidneys .
( a ) chest x - ray showing multiple nodular lesions in both lungs and ( b ) computerized tomography of the brain showing a hyperdense lesion ( arrow ) in the right posterior parietal lobe i wbs [ figure 2a ] and spect / ct [ figure 2b and c ] performed 48 h after oral administration of 2 mci i showed tracer uptake in the head , neck ( residual thyroid ) , bilateral hilar lymph nodes , right third and fourth ribs with lytic changes , lung nodules , s1/s2 spinal canal , right femur , acetabulum and humerus , and multiple exophytic renal nodules .
usg - guided biopsy of a left renal nodule revealed only thyroid follicular cells ( positive for tg immunostaining ) with no pathological evidence of malignancy .
postoperative investigations after 6 weeks showed tg > 3000 ng / ml , anti - tg 30.1 iu / ml , and thyroid stimulating hormone 14.28 iu / ml .
he was treated with 207 mci of i under steroid cover ( prednisolone 40 mg / day ) .
i whole body scan ( a ) 48 h after administration of 2 mci 131i showing increased tracer uptake at multiple sites in the neck , chest , abdomen , pelvis and right thigh .
a small focus of radioiodine uptake is seen on the right side of the head posteriorly ( arrow ) , adjacent to a known focus of tracer contamination ( arrowhead ) .
single photon emission computed tomography / computed tomography of the neck and chest ; ( b ) localizes tracer uptake to residual thyroid , bilateral hilar lymph nodes , right 3rd and 4 ribs with lytic changes and multiple lung nodules .
single photon emission computed tomography / computed tomography of the abdomen ; ( c ) shows tracer uptake in multiple exophytic renal nodules a fifth - day posttherapy whole body planar and spect / ct scan [ figure 3a and b ] confirmed metastasis in the brain ( arrow ) and other sites seen in the pretherapy scan . after an uneventful hospital stay ,
he was discharged on a suppressive dose of thyroxin ( 225 g / day ) .
whole body planar ( a ) and single photon emission computed tomography / computed tomography ( b ) scans 5 days after 207 mci 131i showing increased tracer uptake in the brain ( arrow ) , d11 vertebra , sacrum , and right acetabulum , in addition to residual thyroid and lungs
distant metastases from dtc may present after a latent period of many years . around 10% of the patients with dtc present with multiple sites of distant metastases other than lung , bone , and lymph nodes ,
50% of which involve the brain , 25% the liver , and 25% other sites .
the reported incidence of renal involvement from a primary thyroid malignancy is very rare , being only about 4.5 - 5.9% , whereas of all secondary metastases to the kidneys from all cancers , thyroid cancer constitutes only about 2.5 - 2.7% . so far ,
most of the subjects were female and older than 45 years of age , whereas our patient was an elderly male .
renal metastasis usually appears in the setting of multifocal metastases , as in the present case .
however , in our patient , no pathological evidence of malignancy was identified in any of the surgically resected thyroid specimens .
it is possible that malignancy ( most likely follicular thyroid carcinoma ) might have escaped detection in the left hemi - thyroidectomy specimen 20 years earlier ; a similar case has been reported previously .
apart from a recent onset of cough , our patient was asymptomatic in the presence of renal as well as bone and brain metastases .
metastases from dtc may develop several years ( occasionally decades ) after the removal of the primary thyroid malignancy .
furthermore , they may remain undetected for a long time if no radioiodine intervention is done .
since multiple iodine avid lesions were seen throughout the body on planar scintigraphy , a whole body spect / ct scan was performed for lesion localization .
this helped in precisely localizing abnormal radioiodine uptake in the hilar nodes , lung nodules , kidneys , bone , spine , and brain .
. however , our patient showed radioiodine uptake in the brain metastasis in the presence of radioiodine - avid residual thyroid , renal , and other metastases , which is extremely uncommon .
metastases to the brain are observed in only about 1% of the thyroid carcinomas and , in one study , 23% of the brain metastases were discovered only at autopsy .
the median interval between the diagnosis of dtc and that of brain metastasis was 6.5 years . however , the actual number of reported cases of brain metastases from thyroid carcinoma remains small , and there has been little evidence of benefit from any specific mode of therapy .
the median disease - specific survival from diagnosis of brain metastases was 16.7 months for patients who underwent local excision of one or more brain metastases , compared with 3.4 months for those who did not ( p < 0.05 ) .
our patient had metastatic involvement in multiple organs , which were not amenable to surgery .
the patient 's condition improved symptomatically with absence of any cough during the 2 months following iodine treatment ; he is currently doing well under regular follow - up . to conclude ,
metastatic dtc should be suspected in asymptomatic patients with incidentally detected lesions , raised serum tg and history of thyroid lesions .
 a 65-year - old patient , with a history of left hemi - thyroidectomy for adenomatous goiter 20 years previously , was found to have pulmonary lesions on chest x - ray , a brain lesion on computerized tomography ( ct ) , and elevated serum thyroglobulin ( tg ) . while completion thyroidectomy revealed that no pathological evidence of thyroid malignancy , radioiodine - avid pulmonary , brain , and renal and bone lesions were identified on diagnostic as well as posttherapy whole body planar scintigraphy and single photon emission computed tomography - ct . 
 subsequent ultrasonography - guided biopsy of a renal nodule showed thyroid follicular cells . 
 this case suggests that metastatic differentiated thyroid carcinoma should be suspected in asymptomatic patients with incidentally detected lesions , raised serum tg , and history of thyroid lesions . 