Parathyroid Adenoma within the Carotid Sheath

Abstract

Objective.

Ectopic parathyroid adenoma is an uncommon cause of primary hyperparathyroidism. Apart from the usually described sites of ectopic parathyroid adenoma, anecdotal case reports of undescended parathyroid adenoma along the carotid artery have been described.

Methods.

We report a rare case of a 4 cm large parathyroid adenoma within the carotid sheath.

Results.

A 27-year-old lady presented with severe bony pains, history of height loss, fracture of left shaft femur following trivial trauma and renal calculi. On evaluation she had hypercalcemia with elevated iPTH suggestive of primary hyperparathyroidism. Ultrasound of neck and 99mTc sestamibi SPECT/CT incorrectly localised the lesion as right inferior parathyroid adenoma leading to a failed initial surgery. Later CECT of the neck identified adenoma posterior to right common carotid artery which was confirmed on repeat surgery and the patient was cured.

Conclusion.

Ectopic parathyroid adenomas are both difficult to localise and are a common cause of failed initial parathyroid surgery. Surgeons should exercise caution while removing a visually normal parathyroid gland. In case of any discordance with the pre-operative localization, a meticulous systematic dissection using the conventional approach should be performed and the possibility of an undescended gland in the carotid sheath should be considered.

Introduction

Parathyroid adenoma is the most common cause of primary hyperparathyroidism (1). Amongst these, about 6-22% of the adenomas are found in ectopic sites. The superior and inferior parathyroid glands originate from the fourth and the third branchial pouch respectively. Due to the longer embryologic migration tract, inferior parathyroid glands are more likely to be found in ectopic locations or incompletely descended. The common ectopic locations described are thymus (24–38%), retro-oesophageal space (22–31%), thyroid gland (7–18%) and mediastinum (6–20%). Ectopic parathyroid adenoma often poses diagnostic challenge and is the most common reason for failed initial parathyroid surgery (2). Of the various ectopic locations, adenoma in the carotid sheath has been rarely described (3). We report a case of missed adenoma during initial surgery which was later localized within the carotid sheath.

Case report

A 27-year-old lady presented with complaints of generalized severe bony pains for 6 years due to which she was bed-bound. She also had history of height loss, fracture of left shaft femur following trivial trauma and renal calculi. There was no family history of renal calculi, pathological fractures or neck surgery. On biochemical evaluation she had hypercalcemia (serum calcium - 12 mg/dL, normal 8.5-10.5 mg/dL), hypophosphatemia(serum phosphorus 2.4 mg/dL, normal 2.5-5.5mg/dL) and raised alkaline phosphatase (955 U/L,normal 50-130 U/L). Her intact parathormone (iPTH) was elevated (981pg/mL, normal 14-75pg/mL) with normal serum creatinine and 25-hydroxyvitamin D. Ultrasound of kidneys revealed multiple right renal calculi. A diagnosis of primary hyperparathyroidism was made and localization studies were done. Ultrasound of neck showed a hypoechoic heterogeneous lesion (measuring 20 × 15 mm) in posteroinferior aspect of right thyroid lobe with increased vascularity, reported as right inferior parathyroid adenoma. 99mTc sestamibi scintigraphy with single-photon emission computed tomography (SPECT) and computed tomography (CT) (SPECT/CT) also showed a soft tissue density nodule (2.3 × 2 × 3.6 cm) with increased radiotracer uptake in the right paratracheal region posterior to thyroid gland suggestive of right inferior parathyroid adenoma. Parathyroidectomy was performed and intra-operatively surgeons encountered a normal looking right inferior parathyroid, which was removed in view of 99mTc sestamibi report. Histopathology specimen identified a normal parathyroid gland with no evidence of adenoma and postoperatively the patient continued to have hypercalcemia (serum calcium 14.4 mg/dL) with elevated iPTH (959 pg/mL). In view of persistent hyperparathyroidism a contrast-enhanced CT (CECT) neck was done which revealed a tumor posterior to the right common carotid artery. Repeat surgery was done and after considerable dissection of the carotid sheath, a large 4 cm parathyroid adenoma was identified posterior to the right common carotid artery. Adenoma was confirmed on histopathology and post-surgery, the patient had normal serum calcium (10.5 mg/dL) and iPTH (31 pg/mL).

Figure 1.

Gross specimen of the excised parathyroid adenoma measuring 4 X 2.5 X 2.5 cm.

Figure 2.

Contrast-enhanced CT neck showing the ectopic parathyroid adenoma (blue arrow) posterior to the right common carotid artery (red arrow).

Figure 3.

A) 100x Encapsulated tumor comprising of mainly chief cells in sheets and nests. B) 400x Cells showed mild pleomorphism with centrally placed round nuclei and clear to eosinophilic cytoplasm. No cellular atypia or mitotic activity was noted.

Discussion

Primary hyperparathyroidism commonly presents with bony pains, fractures, renal calculi and parathyroid adenoma is the most common (in 80-85% of all patients) etiology (1). A proportion of adenomas are found in ectopic locations due to the defect in migration of the gland (2,3). Anecdotal case reports of undescended parathyroid adenomas along the carotid artery have been described. Lee et al. described only one case of parathyroid adenoma in carotid sheath among 600 parathyroid surgeries performed at three tertiary centers (4). Similar to this, Rioja et al. observed a single case of adenoma in the vicinity of carotid bifurcation of the 598 surgeries performed for primary hyperparathyroidism (5). On an extensive literature search, only 17 cases of parathyroid adenoma in and around the carotid sheath were found. Amongst these, 8 were located within the carotid sheath, 7 were located at or near the carotid bifurcation and 2 posterior to the common carotid artery.

Of the 17 previously reported cases of parathyroid adenoma around the carotid sheath, 99mTc sestamibi was performed in 13 patients of which adenoma was localized in 11 patients. Mahajan et al., described the utility of SPECT/CT over 99mTc sestamibi dual-phase scintigraphy. In the case reported by them, SPECT/CT revealed an undescended adenoma which was missed on dual-phase due to overlapping submandibular gland activity (6). Similarly, Ezzine et al. reported a case of hyperplasia of left carotid sheath parathyroid gland in a case of chronic renal failure with secondary hyperparathyroidism which was localized by SPECT/CT and was initially missed on dual-phase scintigraphy. They emphasized the importance of inclusion of high cervical region in the field of view to avoid missing undescended parathyroid adenoma (7). In our case, the initial 99mTc sestamibi scintigraphy described the location of adenoma posterior to the thyroid, which usually indicates parathyroid gland of superior origin. However, it was inaccurately reported as right inferior adenoma due to inadequate knowledge about such rare locations, highlighting the limitations in interpretation of imaging techniques.Unavailability of CT films during the initial surgery also led to removal of a normal inferior parathyroid. Later a CECT neck localized a large 4 cm tumor posterior the right carotid artery, which was confirmed during surgery. An important learning point from our case is that surgeons should exercise caution while removing a visually normal parathyroid gland, especially when the anticipated adenoma is big in size. In case of any discordance with the pre-operative localization, a meticulous systematic dissection using the conventional approach should be performed. This is even more relevant in young patients with primary hyperparathyroidism who can have a genetic form of primary hyperparathyroidism, where exploration of all four glands should be performed.

Sanders et al., reported a similar case where SPECT/CT falsely localized the adenoma and later a repeat SPECT coregistered with dedicated neck CT localized the adenoma to the left carotid sheath (8). A distinct feature in our case was the large size of ectopic parathyroid adenoma. We could come across only one similar case by Malm et al.. They reported a case of parathyroid adenoma of 4 cm size located within the carotid sheath, identified by CECT neck which was performed after an initial negative 99mTc sestamibi (9).

Similar to our case, most of the cases required multiple surgeries due to a lack of awareness and failure of isotope studies to localize the lesion around the carotid artery.

Rioja et al. described a case of undescended parathyroid adenoma in the vicinity of carotid artery bifurcation. In the patient, an initial bilateral neck exploration revealed a left inferior parathyroid adenoma but as hypercalcemia persisted later a CT scan identified a second undescended adenoma of the fifth gland which was confirmed after repeat surgery (5). Doppman et al. described 3 cases of parathyroid adenoma within the carotid sheath which were difficult to localize and required multiple surgeries of which one case was cured after 5 surgeries. They reported that the adenomas were found behind the vascular trunks and considerable dissection was required to locate the adenoma even after the sheath was open (10). Our surgeons also had a similar experience in localizing the adenoma, requiring extensive dissection once the carotid sheath was open.

In conclusion, this was a rare case of a large parathyroid adenoma within the carotid sheath posterior to the right common carotid artery. The surgeons must consider the possibility of an undescended gland in the carotid sheath, particularly when parathyroid adenoma is not to be found in the normal position.

Conflict of interest

The authors declare that they have no conflict of interest.

Funding

The authors received no financial support for the research, authorship, and/ or publication of this article.