Thyroid scintigraphy and uptake

A report skeleton for 99mTc-pertechnetate or 123I thyroid scintigraphy, with an optional uptake measurement (RAIU or TcTU). It uses the interpretation and reporting terms of the joint EANM/SNMMI 2019 guideline.

Based on: EANM practice guideline/SNMMI procedure standard for RAIU and thyroid scintigraphy (Giovanella 2019)

THYROID SCINTIGRAPHY [AND UPTAKE]

CLINICAL INDICATION:
  [Hyperthyroidism, cause? / thyroid nodule, function? / multinodular goitre / indeterminate cytology (Bethesda III / IV) / ectopia / congenital hypothyroidism / other]
  TSH [ ] mU/L; FT4 [ ]; FT3 [ ]; TRAb [ ] (dates)
  Ultrasound: [nodule site, size, TI-RADS category / not available]
  Iodine exposure and medication: [iodinated contrast (date) / amiodarone / levothyroxine / antithyroid drug (stopped [ ]) / none]

TECHNIQUE:
  Radiopharmaceutical: [99mTc-pertechnetate [ ] MBq IV, imaged at [15–20] min / 123I-sodium iodide [ ] MBq orally, imaged at [ ] h]
  Views: [anterior neck, parallel-hole / pinhole collimator; with and without markers (sternal notch, palpable nodule); obliques / SPECT(/CT) for substernal or ectopic tissue]
  Uptake: [not measured / 99mTc-pertechnetate uptake (TcTU) [ ]% / RAIU [ ]% at [4–6] h and [ ]% at 24 h]
  Local normal range: [ ]% (range established for this department)

COMPARISON:
  [Prior thyroid scan / ultrasound dated [ ] / none]

FINDINGS:
  Location: [normal cervical / substernal extension / ectopic: lingual / thyroglossal / other]
  Size and shape: [normal butterfly shape / enlarged / U-shaped / asymmetrical]; pyramidal lobe: [seen / not seen]
  Distribution: [homogeneous / heterogeneous]
  Overall uptake compared with salivary glands: [less than / equal to / more than salivary activity]
  Background: [low / normal / high]
  Nodules (compared with extranodular tissue, correlated with ultrasound):
    [site, ultrasound size]: [hypofunctioning (cold) / isofunctioning (warm) / hyperfunctioning (hot)]; extranodular tissue [normal / reduced / suppressed]
  Uptake value: [ ]% ([below / within / above] the local normal range)

PATTERN:
  [Diffuse overactivity, homogeneous distribution, reduced salivary uptake and low background: consistent with Graves' disease]
  [Unifocal or multifocal overactive area(s) with reduced or suppressed uptake elsewhere in the gland: consistent with autonomously functioning thyroid nodule(s)]
  [Multiple mixed areas of focally increased and suppressed uptake: consistent with toxic multinodular goitre]
  [Globally decreased uptake: consistent with destructive thyroiditis, factitious thyrotoxicosis or iodine overload, interpreted with current thyroid function tests and iodine history]

IMPRESSION:
  1. [Pattern and most likely diagnosis]
  2. [Functional status of each nodule, e.g. the [site] nodule is hyperfunctioning (autonomous) / hypofunctioning]
  3. [Recommendation, e.g. hypofunctioning nodule: assess with ultrasound (TI-RADS) and FNA as indicated]

Before you sign

• Interpret the scan with the current TSH and the ultrasound. Match every nodule on the scan to its ultrasound position and size.
• Classify each nodule against the extranodular tissue: cold (reduced uptake), warm (roughly equal) or hot (increased). A hot nodule has a 96–99% negative predictive value for malignancy, so FNA of an autonomous nodule is generally not needed.
• Most cold nodules (up to 80–90%) are benign, so a cold nodule is not a diagnosis of cancer. Send it on to ultrasound and TI-RADS assessment.
• Normal uptake ranges depend on iodine intake. Quote your department's own range, not a textbook one. As a guide, RAIU above 25% in iodine-sufficient regions with clinical hyperthyroidism is compatible with hyperfunction.
• Before calling thyroiditis on low uptake, ask about iodine: iodinated contrast suppresses uptake for 1–2 months and amiodarone for 3–6 months (withdrawal times, EANM/SNMMI Table 3).
• Pertechnetate is trapped but not organified. Rarely, a nodule can look different on pertechnetate and radioiodine scans (a trapping-only nodule); use 123I when an organification defect is suspected.
• In a euthyroid patient with unsuppressed TSH, compensated autonomy can be quantified only after exogenous suppression with thyroid hormone.

Sources

1. Giovanella L, Avram AM, Iakovou I, et al. EANM practice guideline/SNMMI procedure standard for RAIU and thyroid scintigraphy. Eur J Nucl Med Mol Imaging. 2019;46:2514–25.
2. Tessler FN, Middleton WD, Grant EG, et al. ACR Thyroid Imaging, Reporting and Data System (TI-RADS): white paper of the ACR TI-RADS committee. J Am Coll Radiol. 2017;14:587–95.
3. Cibas ES, Ali SZ. The 2017 Bethesda system for reporting thyroid cytopathology. Thyroid. 2017;27:1341–6.