Parathyroid Scan (Parathyroid Scintigraphy)

A parathyroid scan is a nuclear medicine imaging test used to detect abnormal parathyroid glands, primarily in cases of hyperparathyroidism (excessive parathyroid hormone production). It helps locate parathyroid adenomas, hyperplasia, or, rarely, parathyroid cancer.

Common Parathyroid Imaging Techniques:

1. Sestamibi Scan (Tc-99m MIBI Scan)

   • The most commonly used method.

   • Uses Technetium-99m sestamibi (Tc-99m MIBI), which is absorbed by both the thyroid and overactive parathyroid glands.

   • Over time, sestamibi is retained in abnormal parathyroid tissue longer than in normal thyroid tissue, allowing differentiation.

   • Often performed with single-photon emission computed tomography (SPECT/CT) for better localization.

2. Dual-Phase Sestamibi Scan

   • Early phase: Both thyroid and abnormal parathyroid glands absorb sestamibi.

   • Delayed phase: Normal thyroid tissue washes out sestamibi, but abnormal parathyroid glands retain it, making them visible.

3. Dual-Tracer Technique (Tc-99m MIBI + Tc-99m Pertechnetate or I-123)

   • Uses a second tracer (pertechnetate or I-123) that is only absorbed by the thyroid.

   • Subtracting the thyroid image from the sestamibi image enhances detection of parathyroid adenomas.

Indications for a Parathyroid Scan:

• Primary Hyperparathyroidism (PHPT): Usually caused by a parathyroid adenoma (benign tumor).

• Secondary Hyperparathyroidism (SHPT): Often due to chronic kidney disease.

• Tertiary Hyperparathyroidism: Autonomous overactivity after long-term SHPT.

• Parathyroid Cancer (Rare).

Procedure:

1. Injection of Tc-99m sestamibi intravenously.

2. Early imaging (10-15 min) and delayed imaging (1.5-2 hours) to track retention in abnormal glands.

3. SPECT/CT may be done for precise localization.

Results Interpretation:

• Normal: No abnormal tracer retention after the delayed phase.

• Positive Scan (Adenoma/Hyperplasia): Persistent uptake in one or more parathyroid glands, indicating abnormal function.

Advantages of Parathyroid Scintigraphy:

✅ Highly specific for parathyroid adenomas.
✅ Useful for preoperative localization before parathyroid surgery.
✅ Non-invasive and well-tolerated.