Primary Hyperparathyroidism in an Auto‐Transplanted Parathyroid Gland Within the Sternocleidomastoid Muscle

A 79 year old woman with persistent primary hyperparathyroidism (PHPT) presented after two previous failed neck explorations. Her background revealed a hemithyroidectomy in 1988, followed by completion thyroidectomy for low-grade thyroid cancer. She later developed Primary Hyperparathyroidism (PHPT) and underwent failed neck explorations in 2004 and 2006. In 2004, preoperative localization with ultrasound (USS) and 99mTc-sestamibi (MIBI) scans had suggested a possible right inferior adenoma (on MIBI, not on ultrasound) but at both explorations, no parathyroid glands were confidently identified, and no parathyroid tissue was seen on histology of excised tissue. The identification of normal glands was not documented in the operation reports. Persistent symptomatic hypercalcemia (corrected calcium: 2.87 mmol/L, PTH: 18 pmol/L) led to referral for repeat assessment. A repeat USS and MIBI performed prior to re-referral showed similar findings to those in 2004. Given previous surgical failures, 18F-fluorocholine PET/CT was performed, identifying a 28 mm enhancing nodule within the right sternocleidomastoid (SCM) muscle, highly suggestive of an ectopic parathyroid adenoma (Figure 1). A review of her 1988 operative records revealed prior autotransplantation of devascularized parathyroid tissue into the SCM; no other comments were made in regard to visualisation of the remaining glands at thyroidectomy, and no other parathyroid tissue was seen in the histology of the resected specimens. Genetics testing was performed prior to further neck exploration, and this was negative. At surgical exploration, a collar incision was made, and a palpable abnormality could be identified in the SCM muscle. The SCM was mobilized, and a 2 cm parathyroid adenoma was excised (Figure 2). Intraoperative PTH dropped from 16 to 8 pmol/L. Histopathology confirmed a 0.4 g adenoma composed predominantly of chief cells. Parafibromin staining was not performed given no atypical features were seen on histology. Postoperatively, calcium normalized (2.31 mmol/L), and PTH decreased to 3.9 pmol/L. The patient was discharged on postoperative day one; 6 months postoperatively, her calcium and PTH remain in the normal range, with significant symptom improvement. We report the case of a 79-year-old female presenting with primary hyperparathyroidism (PHPT) due to a parathyroid adenoma arising within an auto-transplanted parathyroid gland. This is a rare occurrence, with few reported cases, occurring occasionally in patients with a hereditary predisposition to parathyroid disease or renal parathyroid disease. Our patient had no such risk factors and had undergone multiple prior failed neck explorations—this case underscores the complexity of re-operative parathyroid surgery and the utility of advanced imaging in these cases. Autotransplantation of parathyroid tissue is commonly performed to prevent hypocalcemia after thyroidectomy. The SCM is a preferred site, though the brachioradialis may be used in cases such as in multiple endocrine neoplasia (MEN) or secondary hyperparathyroidism. Complications include recurrent thyroid cancer, graft hyperfunction, and rarely, parathyroid adenoma formation. Ectopic parathyroid adenomas in auto-transplanted glands are exceedingly rare, particularly in patients without a genetic predisposition [1, 2]. Re-operative parathyroid surgery poses technical challenges, with higher complication rates than primary surgery [3]. Accurate preoperative localization is crucial, with 18F-fluorocholine PET/CT (PET-Choline) emerging as a valuable tool due to its high sensitivity (90–96%) in detecting hyperfunctioning parathyroid tissue, particularly in ectopic locations [4, 5]. Compared to traditional imaging such as 99mTc-sestamibi SPECT/CT, it offers superior spatial resolution, shorter scan times, and reduced radiation exposure [4, 5]. Routine use of PET Choline as the preferred first line imaging modality in re-operative Parathyroid cases has been adopted by the institution where this patient presented, given its accuracy in both functional and anatomical assessment of parathyroid disease and its ability to detect ectopic parathyroid tissue—which this interesting case demonstrates. This case underscores the importance of reviewing prior operative records in patients undergoing re-operative parathyroid surgery to identify potential ectopic sites of re-implanted parathyroid tissue. 18F-fluorocholine PET/CT proves highly beneficial in identifying elusive hyperfunctioning glands, offering a targeted surgical approach. Additionally, advancements in imaging and intraoperative adjuncts like ioPTH can improve cure rates in patients previously deemed “incurable.” William MacFaul: writing – original draft, writing – review and editing. Toby Hulf: writing – review and editing. Shad Khan: supervising, writing – original draft, writing – review and editing. The authors have nothing to report. Consent was taken from the patient as part of the routine consent process pre-operatively for participation in research. Furthermore, consent was obtained for use of the case as a case report/publication. Open access publishing facilitated by Macquarie University, as part of the Wiley - Macquarie University agreement via the Council of Australian University Librarians.