radiology and endocrinology
TRANSCRIPT
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Radiology and Endocrinology
ANATOMY
• Radiography
• Ultrasound
• CT
• MRI
FUNCTION
• Radionuclide Imaging
- Scintigraphy
- PET
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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
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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
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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
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Thyroid - radiography
• Little role
• Thyroid mass diagnosed incidentally on chest radiograph
• Thoracic inlet views may demonstrate tracheal compression
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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
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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
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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
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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
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HyperthyroidismRN uptake
1. Thyroid gland (>95%)Toxic nodular goitre
Diffuse toxic goitre (Graves)
Thyroiditis
2. Exogenous T3/4/iodineIatrogenic
Iodine - induced
(XRay contrast, amiodarone)
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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
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RNI in thyroid disease
• Investigation of hyperthyroidism
• Location of ectopic thyroid tissue (congenital hypothyroidism, retrosternal goitre)
• Little role in thyroid nodules
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1ry Hyperparathyroidism
Type %
Adenomas Single 80
Hyperplasia Chief cell 15
Clear cell 1
Carcinoma 4
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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
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Parathyroid imaging
• US not good at finding ectopic glands
• CT Contrast
Surgical artifacts
• MRI Good for localisation and ectopic glands
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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)
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Adrenal glands
Cortex aldosterone
cortisol
adrenal androgens
Medulla adrenalin
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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
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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
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RNI in Cushings syndrome
ACTH-dependent CS bilat
pituitary/ectopic
ACTH -independent CS
bilat nodular hyperplasia bilat
adrenocortical adenoma uni
Adrenocortical carcinoma bilat
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Cushings syndrome
Diagnosis - biochemistry
Localisation - CT/MRI
for
1. Pituitary ACTH-dependent
2. Ectopic ACTH-dependant
3. ACTH - independant
RNI not usually necessary
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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
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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)
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Adrenal medullary RNI
Phaeochromocytoma
Paraganglioma
Neuroblastoma
Ganglioneuroblastoma
Ganglioneuroma
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Adrenal medullary RNI
• Metaiodobenzylguanidine (MIBG)
- localises in catecholamine storage vesicles of adrenergic nerve endings
- 123 I or 131 I
• somatostatin receptor imaging111 In octreotide
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MIBG
• phaeochromocytomas (95% sensitivity)
• neuroblastoma (80 - 90% sens)
• carcinoid
• medullary thyroid carcinoma
(MEN syndromes)
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Phaeochromocytomas
10% malignant
bilateral
extra- adrenal
paediatric
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PhaeochromocytomasDiagnosis - biochemistry
Localisation
CT if > 2cm
RNI to exclude - small tumours
- bilateral adrenal
- multifocal
- metastases
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‘Incidentalomas’
Incidental adrenal mass in patients undergoing abdominal imaging (2%)
Q. Is it functioning?
Is it benign or malignant?
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Functioning ‘incidentalomas’
Diagnosis
Clinical features
Biochmistry
Confirmation
RNI
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Non-functioning
Non-functioning adenoma vs. metastasis
• CT using attenuation values
• MRI - chemical shift imaging
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Radiology and Endocrinology
Localisation
not
Diagnosis
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IMAGING
and the
ENDOCRINE SYSTEM