Ectopic thyroid presenting as a gallbladder mass

Abstract

The ectopic thyroid tissue is the result of abnormality in embryological development and migration. Ectopic thyroid tissue located in or adjacent to the gallbladder wall is extremely rare with only two cases reported since 1969. These cases were all identified incidentally by pathological examination after cholecystectomy for acute or chronic cholecystitis. We here report a case of ectopic thyroid tissue presenting as a gallbladder mass in a 60-year-old woman who underwent cholecystectomy. Ectopic thyroid tissue in the gallbladder wall was confirmed by histopathology.

Ectopic thyroid is a rare abnormality in embryological development and migration. The most common locations are along the mid-line from the foramen caecum to the mediastinum. Ectopic thyroid in other locations is very rare especially below the diaphragm. Here, we report a case of ectopic thyroid tissue presenting as a mass in the gallbladder wall, which was initially suspected to be gallbladder carcinoma. The literature on ectopic thyroid tissue located in or adjacent to the gallbladder wall was reviewed.

Case history

Clinical presentation

A 60-year-old woman presented with recurring right upper quadrant pain was admitted to our hospital. She had a complicated medical history including hypertension, dysplasia in left kidney and previous appendicectomy. Physical examination showed no significant signs in the abdomen except slight tenderness in the right upper quadrant. Ultrasonography showed no stones in the gallbladder but a focal thickened wall. The blood CA19-9 (60.2 IU/ml) was slightly elevated (normal, 0.001–37.0 IU/ml). The abdominal computed tomography (CT) scan indicated a mass (43Hu) with a clear border measured 19 mm × 17 mm × 11 mm in the body and fundus of gallbladder wall. The mass showed no obvious enhancement after contrast medium administration. The pre-operative diagnosis was gallbladder neoplasm. The patient underwent open cholecystectomy and had an uneventful postoperative course. This patient was first followed up 4 weeks after discharge from hospital. Thyroid function showed T3, T4 and TSH levels in the normal range. Emission computed tomographic scintigraphy and CT demonstrated a normal thyroid gland in its expected position. Pelvic ultrasonography showed no obvious abnormality in bilateral adnexa. She refused to undergo a whole body scan with ¹³¹I. However, the whole body CT scan performed in her fifth follow-up (36 months) failed to find any mass lesion in the thyroid or any other metastatic foci.

Pathological presentation

The gallbladder was 60 mm × 30 mm × 20 mm, and a cystic mass approximately 18 mm × 15 mm × 10 mm, filled with colloid-like substance, was found in the gallbladder wall after excising subserosal layer. Unfortunately, the colloid-like substance was not sent for pathological assessment because the cystic mass was excised immediately after resection of the gallbladder.

Histopathological examination showed mild, chronic inflammation in the gallbladder wall. In the body and fundus wall, well-differentiated thyroid follicular tissue was found in the subserosal tissue. The histological diagnosis was confirmed by immunohistochemical staining on the sections which showed positive immunoreactivity of thyroglobulin (TG), thyroid transcription factor-1 (TTF-1) within the follicular cells (Fig. 1).

Figure 1.

(A) Histological examination revealed well-differentiated ectopic thyroid follicles in the subserosal layer of the gallbladder wall (H&E, × 100), which showed no morphological features of cellular atypia including nuclear grooving, nuclear cytoplasmic inclusions and psammoma bodies. (B) Immunohistochemical examination showed positive immunoreactivity of thyroglobulin (TG) of the ectopic thyroid tissue specimen (×100).

Discussion

Ectopic thyroid gland tissue is an unusual finding with the estimated frequency of 0.17 per 1000 patients.¹ The incidence of clinically detectable ectopic thyroid is unknown because the majority of cases are asymptomatic. The most common location for this abnormal development is in the mid-line of the neck between foramen caecum and the thyroid. Ectopic thyroid tissue is extremely rare below the diaphragm and always diagnosed by pathological examination after surgical excision of the lesion. We reviewed the PubMed English literature and summarised that such cases occur in places including duodenum, porta heptis, liver, pancreas, adrenal gland, mesentery of the small intestine, fallopian tube, vagina and uterus. To our knowledge, there have been only two reported cases of ectopic thyroid in the gallbladder wall. The first case² was identified occasionally in an unusual contrast-enhanced CT scan were performed, which provided structural anomaly gallbladder with both thyroid tissue and gastric fundic mucosa by Curtis in 1969. The second case³ was found incidentally by pathological examination after cholecystectomy for acute cholecystitis in a 68-year-old man in 2003, and the patient died in the early postoperative period. However, neither of these two reports provided imaging information on this rare abnormality. Besides these reports, there are two other case reports that describe ectopic thyroid tissue adjacent to the gallbladder wall but not within the gallbladder wall.^4,5 In our patient, the ectopic thyroid tissue was found pre-operatively, presenting as a gallbladder mass, which was considered to be malignant initially. Several imaging procedures including thyroid ultrasonography, computed tomography with ⁹⁹Tc, abdominal sufficient information on this rare disease.

Aberrant thyroid tissue should raise suspicion of metastatic disease from primary carcinoma of the thyroid. As to this patient, although the postoperative emission computed tomographic scintigraphy and computed tomography of the thyroid showed no obvious signs of malignancy, the possibility of a metastatic carcinoma origin from an occult thyroid carcinoma should be considered. However, occult thyroid carcinomas are mostly of the papillary type and usually metastasise to the regional lymph nodes rather than to distant organs. Histological examination in our case could not demonstrate cellular atypia, papillary proliferation and psammoma bodies, which are commonly seen in metastatic occult carcinomas of the thyroid. In addition, the patient has been followed up for 36 months, the whole body CT scan failed to find any mass lesion in the thyroid or any other metastatic foci. The possibility of a metastasis from an occult thyroid cancer seems unlikely in our patient. However, long-term follow-up of this patient is still necessary.

Except for the explanation of metastasis of thyroid carcinoma described above, several theoretical speculations have been suggested as to the aetiology of ectopic thyroid tissue including incomplete descent or excessive descent of thyroglossal duct remnants,⁴ parthenogenetic development of germ cells in the early embryological period and dual differentiation from a common potential endodermal cell precursor of the gut.² Though there is no uniform opinion and the aetiology of thyroid ectopia remains unclear up to now, we believe that the last explanation seems to be the logical explanation.

Conclusions

An awareness of the existence of the extremely rare case of ectopic thyroid in gallbladder wall is important to both the surgeon and the pathologist. Incorrect diagnosis of metastasis thyroid carcinoma may result in wrong treatment.

Letter to Editor in response to referee’s comments

As for the additional ¹³¹I examination the reviewer suggested, we have contacted the patient and tried to persuade her to undergo a whole body scan with ¹³¹I. However, she still refused to this examination due to her health situation. She has hypertension and dysplasia in left kidney as mentioned in the manuscript. Recently, she developed nephritis with proteinuria. Most importantly, since the thyroid of the patient was not resected, she was afraid of hyperthyroidism triggered by intake of radioiodine at greater than diagnostic doses. Nevertheless, we convinced the patient to undergo a whole body CT last week (36-month follow-up) in her fifth follow up. We failed to find any mass lesions in the thyroid and any other metastatic foci. We believe that the possibility of a metastasis from an occult thyroid cancer could be ruled out by the clinical and pathological findings.

Figure 2.

(A) Photograph of the resected gallbladder showing a cystic mass under the serosal layer of the gallbladder wall. (B) Ultrasonography showed no stones in the gallbladder but a focal thickened wall. (C) CT scan showed a mass lesion (43Hu) in the body of the gallbladder wall approximately 1.9 × 1.7 × 1.1 cm (axial). (D) Contrast-enhanced CT scan showed no obvious enhancement of the mass in the gallbladder wall (coronal axes).