MIBG case 7 answers
1) What is the likely diagnosis?
(i) There is avid uptake just to the right of the midline at about the level of the aortic root.(ii) Cardiac uptake is low.
This was due to a thoracic phaeochromocytoma which is producing adrenergic peptides. Click here to view images from her thoracic CT
2) Is this a common site?
No, only around 1-3% of all phaeos occur in the chest. 10-15% of all phaeochromocytomas are extraadrenal and intrathoracic lesions account for 10% of these. They most commonly arise in either costovertebral gutter in close association with the sympathetic chain. They may arise from the heart itself, usually occurring in the atrial walls. Anterosuperior mediastinal tumours behave differently and should be distinguished from paravertebral tumours. These tumours are often non-functioning paragangliomas which are larger, more often malignant and occur in older patients3) How can you tell if it is malignant or not?
A phaeochromocytoma is more likely to be malignant if they occur in childhood, as part of a familial condition or if they are either extraadrenal or large (>5cm) intraadrenal tumours. Unfortunately histology is of no use for determining malignancy. Therefore, you can't truly say a phaeochromocytoma is malignant unless it metastasizes.MIBG scintigraphy is very specific for demonstrating residual or metastatic disease. The majority of these tumors are indolent but some advocate lifelong follow-up as metastatic disease can occur more than a decade after apparent curative resection.
At the time of resection, no metastases had been identified and she remains well 6 months later
4) Does the episode of pulmonary oedema suggest any pathophysiology?
Episodes of pulmonary oedema are a well-recognized complication of adrenaline-producing tumours5) Should the patient discontinue their antihypertensives before an MIBG scintigram?
There are a whole list of drugs to avoid before MIBG scintigraphy. Uptake of MIBG is inhibited by blockade of the neuronal uptake pathway for catecholamines ("uptake-1") and by depletion of catecholamine storage vesicle contents, but is not significantly affected by conventional alpha- and beta-adrenoreceptor blocking drugs.Drugs that are known or suspected to do this should be omitted for 7 days prior to the test. Commonly used drugs include some antihypertensives (only labetalol, reserpine, calcium channel blockers), most antidepressants (particularly tricyclics), most classes of antipsychotic (including many antiemetics) and sympathomimetics (particularly the decongestants phenyl- and pseudoephedrine but salbutamol inhalers are probably OK)
The text is entirely the opinion of the author and does not necessarily reflect that of RUH NHS Trust or the Bristol Radiology Training Scheme. Website content devised by Paul McCoubrie.