Residency · Residency · Nuclear Medicine
Salivary Gland Scintigraphy
Introduction
Salivary gland scintigraphy using Tc-99m pertechnetate provides functional assessment of salivary gland uptake, concentration, and excretion. It is a simple, non-invasive study used to evaluate xerostomia, Sjogren syndrome, salivary gland masses (particularly Warthin tumor and oncocytoma), and post-radiation salivary dysfunction. The study assesses all four major salivary glands simultaneously with dynamic quantitative analysis.
Radiopharmaceutical and Mechanism
Tc-99m Pertechnetate
Tc-99m pertechnetate is trapped by salivary gland ductal epithelial cells via the sodium-iodide symporter (NIS). It is concentrated within the glands but, unlike in the thyroid, is not organified. Upon glandular stimulation, pertechnetate is excreted into the saliva. The administered activity is 370 MBq (10 mCi) given as an intravenous bolus.
Normal Biodistribution
Rapid uptake occurs in the parotid and submandibular glands. The thyroid gland also takes up pertechnetate via NIS. Additional physiologic uptake appears in the nasal mucosa, gastric mucosa, and choroid plexus. After salivary excretion, oral cavity activity becomes visible.
Protocol
Acquisition
The patient is positioned supine with the gamma camera anterior to the face. Dynamic acquisition proceeds at one frame per minute for 30 minutes. At 15-20 minutes, a sialogogue (lemon juice or citric acid placed on the tongue) is administered to stimulate salivary excretion. Imaging continues for 10-15 minutes post-stimulation. Regions of interest are drawn over the parotid glands, submandibular glands, and a background region.
Quantitative Analysis
Time-activity curves are generated for each gland. The key parameters assessed include the uptake phase (rate and degree of tracer accumulation), the concentration ratio (gland-to-background ratio at peak), the excretion response (percentage decrease in activity after sialogogue stimulation), and the excretion fraction (normally greater than 50% decrease post-stimulation).
Normal Findings
A normal study demonstrates progressive uptake over 15-20 minutes in all four major glands with symmetric uptake between paired glands. Following sialogogue stimulation, there is a brisk excretion response with greater than 50% decrease in gland activity and a corresponding increase in oral cavity activity.
Clinical Applications
Sjogren Syndrome
Sjogren syndrome is an autoimmune exocrinopathy affecting salivary and lacrimal glands. Scintigraphic findings include decreased uptake and impaired excretion response. The Schall grading system classifies severity: Grade I shows slightly delayed uptake with normal excretion, Grade II shows delayed uptake with mildly reduced excretion, Grade III shows markedly reduced uptake with severely impaired excretion, and Grade IV shows absent or near-absent uptake and excretion. Salivary scintigraphy is part of the ACR/EULAR classification criteria for Sjogren syndrome, though lip biopsy remains preferred for definitive diagnosis.
Xerostomia Evaluation
Scintigraphy quantifies functional impairment in patients reporting subjective dry mouth, differentiating salivary gland dysfunction from other causes of xerostomia. It serves as a useful baseline before radioiodine therapy or radiation therapy and allows documentation of improvement or decline over time. Asymmetric findings may point to unilateral gland pathology.
Post-Radiation Salivary Dysfunction
Radiation to the head and neck region causes dose-dependent salivary damage. Scintigraphy documents the severity of dysfunction and monitors recovery. The threshold for permanent damage is approximately 25-30 Gy delivered to the parotid glands. Intensity-modulated radiation therapy (IMRT) reduces salivary damage by sparing the glands more effectively.
Radioiodine-Induced Sialadenitis
I-131 therapy for thyroid cancer can cause salivary gland inflammation because NIS-mediated concentration of radioiodine in salivary tissue produces radiation damage. Scintigraphy documents pre- and post-therapy salivary function. Whether sialogogue administration during I-131 therapy protects the glands remains debated.
| Condition | Uptake Pattern | Excretion Response | Key Finding |
|---|---|---|---|
| Normal | Symmetric, progressive | >50% decrease post-sialogogue | Brisk excretion |
| Sjogren syndrome (Grade III-IV) | Markedly reduced | Severely impaired/absent | Bilateral dysfunction |
| Warthin tumor | Focal increased (hot) | Normal in surrounding gland | Only common hot salivary mass |
| Oncocytoma | Focal increased (hot) | Normal in surrounding gland | Rare; similar to Warthin |
| Pleomorphic adenoma | Focal decreased (cold) | N/A | Most common salivary tumor |
| Malignant tumor | Focal decreased (cold) | N/A | Cannot distinguish from pleomorphic adenoma |
| Obstructive sialadenitis | Retained activity | No response to sialogogue | Stone impacting excretion |
| Post-radiation | Diffusely reduced | Impaired | Dose-dependent (>25–30 Gy) |
Salivary Gland Masses
Warthin tumor (papillary cystadenoma lymphomatosum) shows increased uptake (a hot nodule) because it contains oncocytic epithelium with abundant mitochondria and NIS expression. Oncocytoma also demonstrates increased uptake for similar reasons. In contrast, pleomorphic adenomas and malignant tumors are typically cold, showing decreased or absent uptake. The specificity of scintigraphy for mass characterization is limited, and MRI with contrast remains the primary modality for evaluating salivary gland masses.
Interpretation Pitfalls
Asymmetric normal variant uptake may simulate unilateral pathology. Recent food intake can stimulate glands and alter the baseline. Medications affecting salivary function, particularly anticholinergics and antihistamines, should be withheld before the study. Superimposed thyroid activity may complicate submandibular gland assessment. Obstructive sialadenitis caused by a ductal stone shows retained activity without an excretion response to sialogogue stimulation.
Alternative and Complementary Studies
Ultrasound is the first-line modality for evaluating salivary gland masses and ductal calculi. MR sialography provides non-invasive ductal imaging without radiation. Minor salivary gland biopsy remains the gold standard for diagnosing Sjogren syndrome. Salivary flow rate measurement offers a quantitative functional complement to scintigraphy.
Clinical Pearls
Normal salivary gland scintigraphy demonstrates symmetric uptake in all four major glands with greater than 50% decrease in activity following sialogogue stimulation. Warthin tumor and oncocytoma are the only common salivary gland neoplasms that demonstrate increased Tc-99m pertechnetate uptake; most malignant tumors appear as cold lesions. Salivary scintigraphy provides objective quantification of dysfunction in Sjogren syndrome, with grading from I (mild) to IV (severe) based on uptake and excretion impairment. Pre-treatment baseline salivary scintigraphy is valuable before I-131 therapy or head and neck radiation to document existing function and enable post-treatment comparison.
References
- Klutmann S, et al. "Quantitative Salivary Gland Scintigraphy." J Nucl Med Technol. 1999;27(1):20-26.
- Vitali C, et al. "Classification Criteria for Sjogren's Syndrome: A Revised Version of the European Criteria." Ann Rheum Dis. 2002;61(6):554-558.
- Bohuslavizki KH, et al. "Salivary Gland Protection by Amifostine in High-Dose Radioiodine Treatment." J Nucl Med. 1998;39(7):1237-1242.
- Kim YH, et al. "Salivary Gland Scintigraphy in Patients with Sjogren Syndrome: Systematic Review and Meta-Analysis." Clin Nucl Med. 2014;39(10):879-885.