Neurogenic tumours

Over 70% of tumours express somatostatin receptors. Imaging is obtained 4 hours (+/- 24 / 48 hours) after an intravenous infusion. Unfortunately the kidney also has somatostatin receptors, as do areas of inflammation, mammary glands, liver, spleen, bowel, gall bladder, thyroid gland and salivary glands. As such interpretation can be difficult 5.

Octreotide is usually labeled with either 111InDTPA (Octreoscan) or (less commonly) 123I- Tyr3-DTPA 5.

MIBG (metaiodobenzylguanidine)

As many tumours demonstrate uptake with MIBG, it is not specific for phaeochromocytoma. Overall sensitivity is approximately 81% 6.

PET

18F Dopa PET is thought to be highly sensitive according to initial results 3

Treatment and prognosis

Definitive treatment is surgical, and if complete resection is achieved, without metastases, then surgery is curative, and hypertension usually

resolves.

Pre-operative medical management is essential in reducing the risk of intra-operative hypertensive crises and typically consists of non-competitive alpha adrenergic blockade (e.g. phenoxybenzamine). Later (but never before 7-10 days of alpha blockade) a beta blocker may need to be added to control tachycardia or some arrhythmias 5-6.

Metastases from malignant pheochromocytomas are typically to lung, bone and liver 4.

Differential diagnosis

When located in the adrenal gland, the differential is essentially that of an adrenal tumour, and includes :

•adrenal adenoma

•adrenal carcinoma

•adrenal metastasis(es)

In large tumours, especially if malignant, differentiating them from renal cell carcinomas can be difficult, especially on CT.

Adrenal adenoma

An adrenal adenoma is the commonest adrenal mass lesion, and is often found incidentally when the abdomen is imaged. In all cases, but especially in the setting of known current or previous malignancy, adrenal adenomas need to be distinguished from adrenal metastases or other adrenal malignancies.

although in truth an incidental adrenal lesion includes all pathologies (including malignancies). As such, the term should be avoided lest it results in confusion.

Epidemiology

Adrenal adenomas are found in almost all age groups but increase in frequency with age 4.

Clinical presentation

The majority of adrenal adenomas are nonfunctioning, in which case they are asymptomatic.

•calcification

•necrosis

•no fat

•large : > 3 cm

if greater than 4 cm : 70% malignant (excluding adrenal myelolipomas which are easily recognised due to fat, and pheochromocytomas which are usually recognised biochemically)

if greater than 6 cm : 85% malignant 4

CT

CT is often the modality which identifies an adrenal mass. Fortunately using density is

intracellular fat. Lipid-poor adenomas are more difficult to diagnose because the CT numbers increase and approach those of soft tissue.

Adenomas typically have rapid contrast washout, whereas non-adenomas tend to wash out more slowly. There are different protocols, and some controversy exists as to which protocol is the best. A 5 or 10 minute protocol may be more suitable for busy CT lists. However there is evidence that a 15 minutes

post contrast protocol has better diagnostic accuracy11

•non-contrast imaging 4

<0 HU : considered 47% sensitive and

100% specific

<10 HU : considered 71% sensitive and

98% specific

•washout imaging

10 minutes post contrast

< 30 HU 10min post contrast : considered 80% sensitive and 100% specific

>50% washout c.f. to portal venous phase : considered 98% sensitive and 100% specific (this is the most reliable test to differentiate between benign and malignant adrenal lesions 4).

MRI

Chemical shift imaging is the most reliable for diagnosis especially when CT findings are equivocal. Because of the high sensitivity of chemical shift MR imaging to minute amounts of intravoxel fat, MR imaging demonstrates signal intensity loss on opposed-phase images in the majority of adenomas, and a drop in signal intensity of greater than 20% is considered diagnostic for an adenoma 2. Rather

than measuring the signal, one can compare the adenoma in and out of phase, with images windowed similarly (using the spleen or muscle as a reference - NB do not use the liver as it can change signal on in and out of phase imaging depending on presence of heamochromatosis or hepatic steatosis) 4.

As MRIs are usually performed to help indeterminate CT lesions, the sensitivity and specificity depends on the CT density. A drop in signal on out of phase imaging for:

•10-30 HU on CT is 89% sensitive and 100% specific

•10-20 HU on CT is 100% sensitive and 100% specific

Malignant adrenal lesions also demonstrate restricted diffusion 4.

Treatment and prognosis

Small adrenal mass with manifestations of hormonal excess need resection, as do large (> 3 to 5 cm) non functioning adrenal mass lesions as they are considered potentially malignant (see adrenal carcinoma)

Small adrenal lesions with typical features of adenomas and with out

of cases, a pheochromocytoma is a manifestation of an underlying condition including 1-4,6:

•MEN II (both MEN IIa and MEN IIb)

◦account for 3% of all pheochromocytomas

◦almost never extra-adrenal

◦almost always bilateral 4

•von Hippel-Lindau disease

• von Recklinghausen disease (neurofibromatosis type I)

•Sturge-Weber syndrome

•Carney triad : for extra adrenal pheochromocytoma

•tuberous sclerosis

•familial phaeochomocytoma

Clinical presentation

It is rare, but a classical cause of uncontrolled secondary hypertension. A minority of patients will manifest hypertensive crises. In addition to severe paroxysmal hypertension, patients may present with cardiac dysfunction (myocardial infarction, pulmonary oedema) or neurological events (severe headache, visual disturbance, haemorrhagic strokes) 5.

The first investigation in cases where a pheochromocytoma is suspected is usually