Inguinal node metastasis from follicular thyroid cancer.

Sir,

Differentiated thyroid cancers (DTC) are the most common endocrine neoplasm. Regional lymph node metastasis is a very frequent finding in DTC. However, nonregional lymph node metastasis below the diaphragm has been rarely reported in literature in DTC, especially in follicular thyroid cancer.[1]

A 58-year-old female patient presented to the nuclear medicine department our institute with history of tender inguinal swelling since 1 month. She was a known case of follicular thyroid carcinoma. She underwent total thyroidectomy 9 years ago but no radioiodine ablation and was only on suppressive thyroxine therapy. Six months later she developed a left parietal skull swelling which was excised and histopathology showed metastatic follicular carcinoma. Three months later she developed pain in the back and left side of chest. A dorsolumbar spine MRI showed involvement of D7 to L2 vertebrae. She was referred to our center for further management 1 year after surgery. She underwent 131I whole body scan (WBS) which showed remnant uptake of 4.8% at 48 hrs in the thyroid bed and uptake in mediastinal nodes, left chest wall and dorsolumbar vertebrae and was treated with 200 mCi 131I. A further dose of 200 mCi radioiodine was given 8 months after the first dose. She was lost to follow-up for 4 years after which she again presented to us with right gluteal pain. She received the 3rd dose of 200 mCi 131I. The post-therapy scan revealed a metastatic lesion in the right ilium [Figure 1]. She received further three doses of 150 mCi 131I each over a period of next 2 years with good uptake in the metastatic deposits on the post therapy scan. Six months after the sixth dose she presented with a tender right inguinal lymphadenopathy which had not responded to antibiotics. She underwent a fine needle aspiration cytology which revealed features compatible with metastatic follicular carcinoma [Figure 2].

Figure 1

131I whole body scan showing radioiodine uptake in right pelvic region

Figure 2

FNAC from right inguinal node showing cluster of follicular cells (Giemsa ×400)

Patient underwent an 18 F FDG-PET/CT [Figures 3a-d] which showed a large metastatic lesion in the right hip bone infiltrating into surrounding gluteal musculature and right inguinal lymph node 2.5 cm in diameter with intense uptake in the above mass (SUVmax 6.4) and inguinal lymph node (SUVmax 5.2). Serum thyroglobulin was consistently in metastatic range from the time of initial presentation till date (>300 ng/ml).

Figure 3

(a) FDG PET showing intense uptake in right gluteal region, right hip joint and right inguinal node. (b) FDG PET/CT showing intense uptake in right gluteal region, right hip joint and right inguinal node. (c) PET/CT showing intense uptake in right iliac bone and adjacent gluteal muscles. (d) Maximum intensity projection image of FDG PET showing uptake in mass involving right iliac bone and adjacent gluteal muscles, right inguinal node. Also noted is bladder activity

Patient was treated with further dose of 200mci 131I which showed intense uptake in the metastatic lesions. As the cumulative dose has now been 1250 mCi and metastasis is now limited to the right pelvic area the patient has now been planned for external beam radiotherapy.

The presence of inguinal lymphadenopathy in a patient of follicular thyroid cancer is an extremely rare finding. To the best of our knowledge such a finding has not been hitherto reported in literature. Four possibilities can explain the probable mode of metastasis reaching the inguinal node. The first hypothesis is that the inguinal lymphadenopathy reflects tumor embolization from the large metastatic lesion in the right ilium which involved considerable soft tissue in the right gluteal region. However, no other draining lymph nodes were seen to be involved. This attributes to occurrence of a secondary metastatic lesion from a primary metastatic site. The second possibility is direct spread from the primary thyroid cancer. However, isolated inguinal lymphadenopathy in the absence of any other cervical, mediastinal or abdominal nodal involvement is not reported in literature so far in thyroid cancer. Moreover follicular thyroid cancer has greater predisposition to spread hematogenously than via lymphatics. The third possibility is of another coexistent focus of malignant thyroid tissue at a regional site in the pelvis e.g., malignancy in struma ovarii. Most of the cases reported in literature are from papillary thyroid cancer arising in struma ovarii.[23] FDG PET/CT also did not reveal any abnormal uptake/lesion in the ovaries. The fourth and rarest possibility is malignant degeneration of ectopic thyroid tissue in the inguinal node. Although malignant transformation of ectopic thyroid has been described none of the cases have been in subdiaphragmatic location.

In this patient, the first hypothesis seems most plausible. This case illustrates that lymphadenopathy can be a rare manifestation of second degree metastases from a primary metastatic lesion in thyroid cancer. A nonregional lymphadenopathy below the diaphragm in a known case of follicular thyroid cancer should not be brushed aside as infective. We advocate tissue diagnosis in all such nodes particularly if the lymphadenopathy persists after a full course of antibiotics.