Ectopic thyroid tissue in adrenal gland – A case report and review of literature

Abstract

Ectopic thyroid tissue along the line of descent of thyroid from foramen caecum along thyroglossal duct to the normal anatomic location in neck has been reported. Ectopic thyroid tissue in adrenal gland (ETTAG) is rarely encountered and very few cases have been reported in literature. The most common differential diagnosis to be considered when thyroid follicles are noted in adrenal gland are metastasis from a thyroid malignancy or a teratoma or an ectopic thyroid tissue in adrenal gland. We present a case of an adrenal incidentaloma in a young pregnant female which was diagnosed to be ectopic thyroid tissue in adrenal gland. The review of literature of similar cases of this rare embryological aberrance is discussed. To our knowledge, only 16 such cases have been documented in literature and our case is the first one from Indian subcontinent and the largest documented with respect to size.

Introduction

Ectopic thyroid tissue along the line of descent of thyroid from foramen caecum along thyroglossal duct to the normal anatomic location has been reported, in the so called Wölffer’s area [1]. The are reports of ectopic thyroid tissue in areas above the diaphragm and seldom reported in areas below diaphragm like in duodenum, pancreas and liver [2]. Ectopic thyroid tissue in adrenal gland is a very rare presentation and is mostly asymptomatic and diagnosed only by post-surgery histopathological examination. Ectopic thyroid tissue can have all the conditions that involve normal thyroid, like thyroiditis, thyrotoxicosis, as well as malignancy. ETTAG must always be distinguished from a metastasis originating from a thyroid carcinoma. It is extremely difficult to explain the reason for occurrence of ectopic thyroid in adrenal gland but this need to be considered as a differential diagnosis when evaluating cystic adrenal incidentalomas.

Case presentation

A 32-year-old female was incidentally found to have right adrenal mass during her routine ultrasound during first trimester antenatal checkup. She underwent evaluation with serum catecholamines which was normal. She underwent MRI abdomen which showed a 12 cm x 10 cm T2 hyperintense solid cystic lesion in right suprarenal region in hepatorenal space She was diagnosed to have a Non-functional adrenal tumor, and was observed during pregnancy. Patient was advised surgery for the adrenal tumor during the third trimester but she defaulted. She presented 6 months after delivery with complaints of abdominal distention and increase in size of swelling associated with dull aching abdominal pain. In view of the size of tumor and increase in size, she underwent re-evaluation with CECT abdomen and a whole-body PET CT which showed a 13 × 10 cm right adrenal mass with low FDG avidity (Fig. 1). She was also found to have a 3 × 3 cm left thyroid nodule. She had a past history of right hemithyroidectomy, at some other hospital 10 years back for a benign thyroid nodule and the histopathology was reported as benign colloid nodule. USG neck revealed TIRADS 2 nodule in left lobe of thyroid with no cervical lymph nodes. FNAC of left thyroid nodule was done and was reported as benign colloid nodule (Fig. 2). Her thyroid function test was normal. She underwent Right adrenalectomy. Post operative period and recovery were uneventful.

Fig. 1

A) CECT abdomen showing a right adrenal mass B) PET CT showing adrenal mass with low FDG avidity

Fig. 2

Fine needle aspiration cytology of left thyroid nodule- benign colloid nodule (high and low power view)

Histopathology

Histopathology revealed a single globular mass of size 14 × 13 × 5 cm weighing 1045gms. External surface- grey white, globular, smooth and Cut surface extruded gelatinous material with capsule. (Fig. 3) Well circumscribed lesion with solid and cystic components were noted. Microscopy revealed a well circumscribed lesion showing thyroid follicles of varying sizes, filled with colloid and overlying area of thin rim of compressed normal adrenal tissue (Fig. 4). No evidence of overt atypia noted in the thyroid follicular cells. Immunohistochemistry for thyroglobulin and TTF-1 were positive (Fig. 5) confirming thyroid origin. Further Immunohistochemistry was done to check for an adrenal metastasis from thyroid malignancy. Immunohistochemistry for CK 19, Galectin 3 and HBME 1 were negative (Fig. 6). The tumour blocks were sent for BRAFV600 mutation analysis and No V600 mutation was detected in the given specimen.

Fig. 3

Right adrenal cystic mass of size 14 × 13 × 5 cm weighing 1045GMS

Fig. 4

Well circumscribed lesion showing thyroid follicles of varying sizes, filled with colloid

Fig. 5

Immunohistochemistry to confirm thyroid origin- thyroglobulin and TTF-1 are positive. A) TTF1 positive B) thyroglobulin positive

Fig. 6

Immunohistochemistry to rule out metastasis from thyroid malignancy- CK 19, galectin 3 and HBME 1 were negative. A) CK 19 negative B) galectin 3 negative C) HBME 1 negative

Discussion

The thyroid tissue develops during the fourth embryonic week as thyroid primordium from endoderm at foramen caecum and by the seventh week, penetrates the underlying mesoderm, descends to the adult position in the neck anterior to trachea. During its descent it is attached to foramen caecum by thyroglossal duct. Ectopic thyroid gland along this pathway of thyroglossal duct can be seen in neck, the mediastinum, the pharynx or the larynx. Outside the route of embryonal descent, intra-abdominal thyroid tissues have been reported in sites like gallbladder, the mesentery of the small intestine, the pancreas, and the space posterior to the spleen and stomach [2,3,4].

Thyroid develops from endoderm and most ectopic thyroid deposits are also found in endodermal derivatives whereas adrenal cortex is derived from Intermediate mesoderm and medulla is derived from ectodermal neural crest cells. So, the possible explanation for ETTAG could be due to the presence of adrenal stem cells with propensity to develop thyroid tissue [5]. To our knowledge this case is just the 17th case of ETTAG reported in literature in 15 publications (Table 1) and is the first one to be reported in a pregnant female in Indian subcontinent. A review of literature of previous cases shows that ETTAG is more common in female (16:1) and usually cystic in nature and most commonly presents as an adrenal incidentaloma diagnosed with either CT or MRI with normal Thyroid function tests and normal serum catecholamine levels. The initial few cases were reported mainly from Japan [8,9,10,11,12,13] and the age of presentation is from 29 to 67 years. There is no right or left predominance in presentation. Lesions were 8 mm to 8 cm in size and compared to the previous cases, this is the largest reported in size and weight measuring around 14 cm and weighing around 1 kg.

Table 1 Reported cases of ETTAG in literature

It is important to distinguish this condition from metastatic thyroid cancer. Adrenal metastasis from thyroid cancers though rare have been reported and should be the first differential to be considered in case of histopathology showing thyroid follicles in adrenal gland [6]. Hence all these patients need to undergo clinical radiological and FNAC to rule out a thyroid malignancy. In a few cases, patients underwent total thyroidectomy to rule out malignancy. Our patient too had an Ultrasound which showed colloid nodules and no evidence of malignancy in thyroid. Metastasis from thyroid cancer can be extremely well differentiated and difficult to distinguish from ectopic benign thyroid deposit. Meyer and Steinberg’s proposed criteria for the differential diagnosis of non-neoplastic thyroid tissue from metastatic thyroid cancer; microscopic size, round or oval follicles, nonpapillary pattern, uncrowded nuclei, and the absence of stromal proliferation or psammoma bodies indicate a nonneoplastic lesion [7]. IHC for CK19, galectin-3 or HBME 1, molecular analysis for BRAF or RAS mutations might be helpful to diagnose metastasis from thyroid carcinomas. The other differential diagnosis to be considered is that of a teratoma. But in none of the previous cases reported, the histopathology had any evidence of any other tissue components to suggest the ectopic thyroid is a teratoma/choriostoma.

Conclusion

Ectopic thyroid tissue is a rare entity and is usually found along the route of embryonal descent and rarely reported in adrenal gland. Aberrant descent of embryological tissue can justify Ectopic thyroid in sites such as the heart, mediastinum, and at mid-subdiaphragmatic locations like the porta hepatis and duodenum but do not explain its presence in adrenal gland. These are mostly cystic adrenal masses detected incidentally and are diagnosed only on histopathological examination. When thyroid tissue is identified in adrenalectomy specimen the differential diagnosis to be considered are ETTAG, teratoma, or metastasis from a thyroid primary. The relevant literature review and the evaluation in our case helps us better understand this rare pathology and has to be considered as a differential diagnosis in case of cystic adrenal incidentalomas. Thorough thyroid evaluation is mandatory in all patients with ETTAG.