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 - scintigraphy99m 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 scintigraphy99m 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

HyperthyroidismRN uptake

1. Thyroid gland (>95%)Toxic nodular goitre

Diffuse toxic goitre (Graves)

Thyroiditis

2. Exogenous T3/4/iodineIatrogenic

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 imaging111 In octreotide

MIBG

• phaeochromocytomas (95% sensitivity)

• neuroblastoma (80 - 90% sens)

• carcinoid

• medullary thyroid carcinoma

(MEN syndromes)

Phaeochromocytomas

10% malignant

bilateral

extra- adrenal

paediatric

PhaeochromocytomasDiagnosis - 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