Radiology and Endocrinology ANATOMY Radiography Ultrasound CT MRI FUNCTION Radionuclide Imaging - Scintigraphy - PET

Radionuclide Imaging Images metabolic pathways Pharmaceutical which mimics a component of a normal metabolic pathway is administered to the patient Pharmaceutical radiolabelled so that its distribution in the patient can be visualised with a gamma camera

Ideal Radionuclide emits gamma radiation at suitable energy for detection with a gamma camera (60 - 400 kev, ideal 150 kev) should not emit alpha or beta radiation half life similar to length of test cheap readily available

Ideal radiopharmaceutical cheap and readily available radionuclide easily incorporated without altering biological behaviour radiopharmaceutical easy to prepare localises only in organ of interest t1/2 of elimination from body similar to duration of test

Thyroid - radiography Little role Thyroid mass diagnosed incidentally on chest radiograph Thoracic inlet views may demonstrate tracheal compression

Thyroid - ultrasound High resolution (5 - 10 MHz) Confirms - mass is thyroid cystic or solid single or multiple cannot distinguish solid carcinoma from solid dominant nodule Not useful in hyperthyroidism

Thyroid - CT/MRI Not as good as US at resolving lesions within the thyroid Best tests for assessing mediastinal disease CT better than MRI for calcification MRI better than CT for distinguishing between fibrosis and residual tumour

Thyroid - scintigraphy 99m PERTECHNETATE Trapped but not organified Competes with iodide for uptake Cheap and readily available IODINE (123I or 131 I) Trapped and organified Better for retrosternal goitres Expensive, cyclotron generated RECENT (10 days) IODINE CONTRAST BLOCKS UPTAKE

Thyroid scintigraphy 99m Tc 123 NaI ADMIN iv po/iv PATIENT withdraw thyroid Rx PREP avoid high Iodine foods IMAGING 15 min pi 1-2hr pi 24 hr po

Hyperthyroidism RN uptake 1. Thyroid gland (>95%) Toxic nodular goitre Diffuse toxic goitre (Graves) Thyroiditis 2. Exogenous T3/4/iodine Iatrogenic Iodine - induced (XRay contrast, amiodarone)

Thyroid nodules Risk of malignancy Overall 10% US - cystic 0.3 - 10% US - solid ???? RNI - cold 16% RNI - hot 4% First line investigation: Cytology +/- US

RNI in thyroid disease Investigation of hyperthyroidism Location of ectopic thyroid tissue (congenital hypothyroidism, retrosternal goitre) Little role in thyroid nodules

1ry Hyperparathyroidism Type % Adenomas Single 80 Hyperplasia Chief cell 15 Clear cell 1 Carcinoma 4

RN parathyroid imaging 99mTc / 201Tl 99mTc-MIBI subtraction scans early/late scans False positives: thyroid pathology False negatives: parathyroid hyperplasia Both good for ectopic parathyroids

Parathyroid imaging US not good at finding ectopic glands CT Contrast Surgical artifacts MRI Good for localisation and ectopic glands

Imaging parathyroids Uncomplicated 1ry hyperparathyroidsim 90 -95% surgical success rate without imaging Recurrent/persistent hyperparathyroidism surgical success rate without imaging -50% with imaging - 90% (combined RNI + MRI)

Adrenal glands Cortex aldosterone cortisol adrenal androgens Medulla adrenalin

Adrenal glands AXR - may show calcification US - large masses only (unless neonatal) CT - can detect small lesions - cannot distinguish metastases from non-functioning adenomas MRI - small lesions - may distinguish mets from non-functioning adenomas

Adrenal cortical RNI Radiolabelled cholesterol esters (75 Seleno-methylnorcholesterol, 131 I - 6B iodomethyl-19-norcholesterol) Image at 4 and 7 days > 50% difference in activity between sides is abnormal

RNI in Cushings syndrome ACTH-dependent CS bilat pituitary/ectopic ACTH -independent CS bilat nodular hyperplasia bilat adrenocortical adenoma uni Adrenocortical carcinoma bilat

Cushings syndrome Diagnosis - biochemistry Localisation - CT/MRI for 1. Pituitary ACTH-dependent 2. Ectopic ACTH-dependant 3. ACTH - independant RNI not usually necessary

RNI and Cushings syndrome Used for 1. Finding residual functioning adrenal remnants if recurrent disease after prior bilateral adrenalectomy 2. Somatostatin receptor scanning for ectopic ACTH from small bronchial carcinoid tumours

Primary aldosteronism small tumours may not be seen with CT/MRI RNI + dexamethasone suppression can find tumours < 1cm Adrenal visualisation before 5 days is abnormal (bilateral/unilateral)

Adrenal medullary RNI Phaeochromocytoma Paraganglioma Neuroblastoma Ganglioneuroblastoma Ganglioneuroma

Adrenal medullary RNI Metaiodobenzylguanidine (MIBG) - localises in catecholamine storage vesicles of adrenergic nerve endings - 123 I or 131 I somatostatin receptor imaging 111 In octreotide

MIBG phaeochromocytomas (95% sensitivity) neuroblastoma (80 - 90% sens) carcinoid medullary thyroid carcinoma (MEN syndromes)

Phaeochromocytomas 10% malignant bilateral extra- adrenal paediatric

Phaeochromocytomas Diagnosis - biochemistry Localisation CT if > 2cm RNI to exclude - small tumours - bilateral adrenal - multifocal - metastases

‘Incidentalomas’ Incidental adrenal mass in patients undergoing abdominal imaging (2%) Q. Is it functioning? Is it benign or malignant?

Functioning ‘incidentalomas’ Diagnosis Clinical features Biochmistry Confirmation RNI

Non-functioning Non-functioning adenoma vs. metastasis CT using attenuation values MRI - chemical shift imaging

Radiology and Endocrinology Localisation not Diagnosis

IMAGING and the ENDOCRINE SYSTEM