Topic breakdown

1. Endocrine anatomy and physiology (short summary)
2. Imaging modalities: how each works, advantages, disadvantages
3. Pituitary and hypothalamus (adenoma, prolactinoma, acromegaly, Cushing disease, hypopituitarism)
4. Thyroid (goitre, nodules, Graves disease, thyroiditis, cancer)
5. Parathyroid (hyperparathyroidism, adenoma localisation)
6. Adrenal (incidentaloma, Conn, Cushing, pheochromocytoma, adrenal insufficiency)
7. Pancreatic endocrine tumours (insulinoma, gastrinoma, MEN syndromes)
8. Gonads, bone and others (PCOS, osteoporosis, rickets)
9. Imaging selection summary table: which test for which organ

Short overview

• The hypothalamus and pituitary control the other glands. The anterior pituitary releases GH, PRL, ACTH, TSH, FSH and LH. The posterior pituitary releases ADH and oxytocin.
• The thyroid sits in front of the trachea. It makes T3 and T4, which set metabolic rate. C cells make calcitonin.
• The four parathyroids sit behind the thyroid. They make PTH, which raises serum calcium.
• The adrenals sit above the kidneys. The cortex makes aldosterone, cortisol and androgens. The medulla makes catecholamines.
• The endocrine pancreas (islets) makes insulin and glucagon. The gonads make sex steroids.
• Most axes work by negative feedback.

Topic breakdown

1. Endocrine anatomy and physiology (short summary)
2. Imaging modalities: how each works, advantages, disadvantages
3. Pituitary and hypothalamus (adenoma, prolactinoma, acromegaly, Cushing disease, hypopituitarism)
4. Thyroid (goitre, nodules, Graves disease, thyroiditis, cancer)
5. Parathyroid (hyperparathyroidism, adenoma localisation)
6. Adrenal (incidentaloma, Conn, Cushing, pheochromocytoma, adrenal insufficiency)
7. Pancreatic endocrine tumours (insulinoma, gastrinoma, MEN syndromes)
8. Gonads, bone and others (PCOS, osteoporosis, rickets)
9. Imaging selection summary table: which test for which organ

Short overview

• The hypothalamus and pituitary control the other glands. The anterior pituitary releases GH, PRL, ACTH, TSH, FSH and LH. The posterior pituitary releases ADH and oxytocin.
• The thyroid sits in front of the trachea. It makes T3 and T4, which set metabolic rate. C cells make calcitonin.
• The four parathyroids sit behind the thyroid. They make PTH, which raises serum calcium.
• The adrenals sit above the kidneys. The cortex makes aldosterone, cortisol and androgens. The medulla makes catecholamines.
• The endocrine pancreas (islets) makes insulin and glucagon. The gonads make sex steroids.
• Most axes work by negative feedback.

Endocrine diseases and imaging: anatomy, physiology, modalities, indications

1. Anatomy and physiology (very short)

2. Imaging modalities: advantages, disadvantages, indications

Ultrasound (US)

• Advantages:
  • No radiation, cheap and widely available.
  • Real-time imaging, with Doppler for vascularity.
  • Guides fine needle aspiration (FNA).
  • More detailed than scintigraphy for thyroid nodules and the most cost-effective way to screen for thyroid adenoma. It also finds extra nodules in 20 to 48% of patients referred with a "solitary" nodule (K J Lee's Essential Otolaryngology, Endocrine section).
• Disadvantages:
  • Operator dependent.
  • Cannot see retrosternal extension or deep structures well, and is limited in obese patients.
  • Gives no functional information.
• Indications:
  • Thyroid nodule, goitre and thyroiditis.
  • Neck lymph nodes in thyroid cancer.
  • Parathyroid adenoma localisation (first-line with scintigraphy).
  • Ovarian (PCOS) and testicular pathology.
  • FNA guidance.
  • Doppler "thyroid inferno" suggests Graves disease.

Contrast methods

• Advantages:
  • Show vascular anatomy.
  • Sampling localises the hormone source. Inferior petrosal sinus sampling distinguishes pituitary from ectopic ACTH. Adrenal vein sampling distinguishes unilateral from bilateral aldosterone excess. Selective venous sampling localises parathyroid and pancreatic tumours.
• Disadvantages:
  • Invasive, with technical failure and complications.
  • Iodinated contrast can trigger thyrotoxicosis in nodular goitre, and it delays radioiodine uptake and therapy for weeks.
  • Contrast nephropathy and allergy.
  • Radiation.
• Indications: Biochemically proven disease with negative or equivocal cross-sectional imaging. This applies to Cushing disease with a negative pituitary MRI (Bailey and Love, Radiological section), primary aldosteronism when surgery is considered, and occult hyperparathyroidism or insulinoma.

Scintigraphy and nuclear medicine

• Tracers:
  • Tc-99m pertechnetate, or I-123/I-131 (Sabiston, Nuclear Scintigraphy).
  • Tc-99m sestamibi for parathyroid.
  • MIBG for pheochromocytoma and paraganglioma.
  • Octreotide or Ga-68 DOTATATE PET-CT for neuroendocrine tumours (NETs).
  • FDG-PET for dedifferentiated thyroid cancer.
• Advantages:
  • Shows function, not just structure.
  • Whole-body survey for metastases or multifocal disease.
  • Single-session localisation of ectopic tissue (retrosternal goitre, ectopic parathyroid).
• Disadvantages:
  • Low spatial resolution.
  • Radiation dose, and long scan times.
  • False positives, for example sestamibi uptake in thyroid nodules, carcinomas and lymph nodes (Fischer's Mastery of Surgery).
  • Contraindicated or restricted in pregnancy and breastfeeding.
  • Interference from iodine, drugs or recent contrast.
  • Sestamibi is less sensitive for small (<500 mg) glands.
• Indications:
  • Hyperthyroidism with a nodule. Scintigraphy establishes solitary versus multiple hyperfunctioning nodules (Plummer disease) and is paired with US (Sabiston, Ultrasound Evaluation of Thyroid Nodules).
  • Graves versus thyroiditis: diffuse high uptake in Graves, low uptake in destructive thyroiditis.
  • Ectopic thyroid and thyroid cancer remnant or metastases after surgery.
  • Parathyroid adenoma: sestamibi SPECT/CT, sometimes with dual-isotope subtraction.
  • Pheochromocytoma and paraganglioma (MIBG).
  • Neuroendocrine tumours (SSTR PET).

CT

• Advantages:
  • Fast, widely available, with excellent spatial resolution.
  • Best for bone, calcification and the lungs.
  • Measures density (Hounsfield units) and contrast washout.
  • Good for adrenals, pancreas and mediastinum.
  • 4D-CT localises parathyroid adenomas.
• Disadvantages:
  • Ionising radiation.
  • Iodinated contrast has the thyroid and renal problems described above.
  • Poor soft-tissue contrast in the sella compared with MRI.
  • Dental or bone artefact at the skull base.
• Indications:
  • Adrenal mass characterisation. Benign adenomas are low density (<10 HU), while carcinomas tend to be hyperattenuating (>18 HU), heterogeneous and irregular (Bailey and Love, Investigation; Schwartz, Adrenal Incidentaloma).
  • Pancreatic NETs.
  • Retrosternal goitre and tracheal compression.
  • Staging of thyroid cancer (non-iodinated contrast if radioiodine is planned).
  • Ectopic ACTH search: thorax, abdomen and pelvis.
  • Parathyroid 4D-CT.
  • Pituitary only if MRI is contraindicated, in which case it shows bony remodelling.

MRI

• Advantages:
  • Best soft-tissue contrast.
  • No ionising radiation.
  • Multiplanar imaging.
  • Gadolinium is not nephrotoxic at standard doses and does not affect thyroid function.
  • Chemical-shift sequences characterise adrenal adenomas (lipid-rich).
• Disadvantages:
  • Expensive, with long scan times and motion artefact.
  • Contraindicated with some devices and implants, and claustrophobia is an issue.
  • Less sensitive for calcification.
  • Limited lung and bone detail.
  • Gadolinium caution in severe renal failure.
• Indications:
  • Pituitary and hypothalamic region.
    • MRI is the preferred method for pituitary anatomy. The normal gland is under 1 cm in height, and microadenomas appear hypointense on T1 (Goldman-Cecil, Diagnosis; K J Lee's, Radiograph Studies).
    • Used for adenoma, craniopharyngioma, Rathke cleft cyst, hypophysitis and stalk lesions. Look for optic chiasm compression and cavernous sinus invasion.
  • Adrenal masses, for example in pregnancy, children, or when CT is indeterminate.
  • Pancreatic NETs and liver metastases.
  • Parathyroid, as an alternative localisation tool.
  • Neck, for local extension of thyroid cancer.

3. Disease-by-disease: best test

4. Key principles

• Biochemistry first, imaging second. Image only after the hormonal diagnosis is confirmed, because incidentalomas are common.
• Avoid iodinated contrast before radioiodine scanning or therapy, and in thyrotoxic nodular goitre.
• Thyroid: US plus FNA for structure, scintigraphy for function.
• Pituitary: MRI.
• Adrenal: CT density, with MRI as the problem solver.
• Parathyroid: US plus sestamibi SPECT/CT.
• Neural crest and neuroendocrine tumours: MIBG or SSTR PET.