A 50-year-old female presented to our emergency department with pain in the left leg after trivial trauma which on plain radiography was diagnosed as an intertrochanteric fracture of the left femur. On further investigating the patient, the laboratory findings showed increased calcium level (14mg/dl) and serum PTH (1668pg/ml).
Ultrasound examination revealed a large, well-defined, predominantly solid lesion posterior to and closely abutting the right lobe of the thyroid gland, measuring approximately 6.1 x 2.6 cm. Few anechoic cystic areas and foci of macro-calcifications were seen within the lesion (Fig 1). Extensive vascularity was seen on colour doppler (Fig 2).
Parathyroid Tc-99m-sestamibi scan was done which showed a large focus of increased tracer uptake in the right neck in the region of the right thyroid gland of approximately size 5.6 x 3.1 cm. Persistent retention on delayed (50 min and 2 hours) images was seen. Physiological tracer uptake was seen in the left lobe of the thyroid and salivary glands (Fig 3). On dual-isotope subtraction imaging using Tc-99m-pertechnate, there was evidence of residual radioactivity on the subtraction images suggesting a hyperfunctioning parathyroid gland (Fig 4).
An enlarged parathyroid measuring 36gms was removed at surgery (Fig 5) and the diagnosis of giant parathyroid adenoma was confirmed at histopathology.
Hyperparathyroidism is most commonly caused by parathyroid adenoma followed by parathyroid hyperplasia and parathyroid carcinoma. Parathyroid adenoma usually measures up to 1gm, but can rarely weigh more than 3.5gms, then called as Giant parathyroid adenomas .
The exact aetiology is unknown with few known risk factors like radiation exposure and long-term lithium therapy. Most cases are sporadic, however, few syndromes like hyperparathyroidism jaw tumour syndrome and MEN syndromes (MEN1 > MEN2) are associated.
Most patients are identified at the asymptomatic stage due to frequent routine blood investigations . Others may present with abdominal pain, osteopenia, nephrolithiasis, osteitis fibrosa cystica and psychiatric disturbances. Increased calcium and PTH levels are the hallmarks of hyperparathyroidism . This is accompanied by hypophosphatemia and hypophosphaturia.
Parathyroid adenomas can be eutopic (around the thyroid glands) or ectopic. Inferior parathyroid glands are more commonly ectopic than the superior. These locations can be in the thyroid gland, near thymus, retroesophageal area, mediastinum, vagus nerve or the carotid sheath. However, multiple adenomas like double adenomas are more common in superior parathyroid glands.
Ultrasonography and Tc99m SestaMIBI scan are currently the first line of investigation .
Ultrasound with doppler has high sensitivity and specificity for detecting abnormal parathyroid glands. The presence of cysts and macro-calcifications, as seen in our case, are unusual features of parathyroid adenoma which may be confused with thyroid lesions. Presence of these atypical findings have been associated with a higher risk of malignancy  and warrants regular postoperative clinical follow-ups.
Normal parathyroid glands do not show any uptake on the Tc99m SestaMIBI scan. Dual-isotope subtraction is a technique where one radiotracer (Tc-99m-sestamibi) is used for visualization of hyperfunctioning parathyroid and thyroid glands and a second radiopharmaceutical (Tc-99m-pertechnate) is used only for the thyroid gland. The second set of images are deducted from the first set and the retention of contrast in the final image is suggestive of a hyperfunctioning parathyroid gland , as in our case.
4DCT and 18F-FDG PET/CT are used in cases with indeterminate findings on conventional imaging, in ectopic adenomas or multiglandular disease . Preoperative 4DCT has higher diagnostic accuracy as compared to the conventional methods with the added advantage of detection of coexistent thyroid and mediastinal pathologies. Risk-benefit issue must be considered since 4DCT is associated with higher radiation dose.
Contrast-enhanced ultrasound (CEUS) is an emerging modality with similar enhancement pattern as 4DCT.
The treatment of choice of parathyroid adenomas is surgical excision . The conventional technique of classic bilateral neck dissection is now replaced by a minimally invasive procedure called directed parathyroidectomy, which when combined with intraoperative parathyroid hormone assay is associated with higher cure rates and low complication rates.
Hence, accurate preoperative localization of the abnormal parathyroid gland is critical to the success of the directed technique and to avoid recurrences due to improper excision.
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