Neurogenic tumours

the abdomen and 90% limited to the adrenal glands 6.

On CT pheochromocytomas are large usually heterogeneous masses with areas of necrosis and cystic change.

Up to 7% demonstrate areas of calcification 4.

It should be noted, that in patients with suspected phaeochromocytomas contrast may be contraindicated as it could precipitate a hypertensive crisis.

MRI

MRI is the most sensitive modality for identification of pheochromocytomas, and is particularly useful in cases of extra-adrenal location. The overall sensitivity is said to be 98% 6.

◦ areas of necrosis / haemorrhage / calcification will alter signal

•T1 C+ (Gd)

◦heterogenous enhancement

◦enhancement is prolonged, persisting for

as long as 50 minutes 4

Nuclear medicine

A number of agents can be used to attempt to image pheochromocytomas, and are especially useful in trying to locate an extra-adrenal tumour (when CT of the abdomen is negative) or metastatic deposits. Unfortunately these agents are not very specific for pheochromocytomas, and have limited spatial resolution, usually requiring the tumour to be greater than 1cm in diameter.

Octreotide (somatostatin) scans

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.

Ganglioneuroma

immature elements 1. They tend to occur in the paediatric population and are often asymptomatic. Usually, patients are older than 10 years old, compared to neuroblastoma which occurs in patient younger than 3 years old.

Pathology

Pathologically, they are composed of ganglion cells, Schwann cells and fibrous tissue. They are neuroblastic tumours, i.e. arising from primitive cells of the sympathetic system.

Associations

6. multiple endocrine neoplasia type IIb 5-6: particularly with mucosal ganglioneuromas

Location

Can potentially occur anywhere along the peripheral autonomic ganglion sites. The posterior mediastinum one of the commonest locations 2 (~ 40%). Occurrence in retroperitoneum, neck and adrenal gland is also relatively common.

Radiographic features

Lesions are generally well defined and can be quite large at presentation.

CT

Typically seen as well-circumscribed, solid, encapsulated masses. Tend to be iso to hypoattenuating to muscle 8. May demonstrate calcifications (~ 20% 2,4)

MRI

Reported signal characteristics include

•T1 - tends to have homogeneously low or intermediate signal

•T2 - tends to have heterogenously intermediate or high signal

•T1 C+ (Gd) - variable ranging from none to heterogenous enhancement

•ADC - ADC values tend to be higher to that of a neuroblastoma 9

Differential diagnosis

The differential depends on location; for thoracic lesions, consider the differential for a posterior mediastinal mass.

Pheochromocytoma

Pheochromocytomas is an uncommon tumour of the adrenal gland, with characteristic clinical, and to a lesser degree, imaging features. The tumours are said to follow a 10% rule :

7.~ 10% are extra-adrenal

8.~ 10% are bilateral

9.~ 10% are found in children

10.~ 10% are familial

11.~ 10 % are not associated with hypertension

Epidemiology

The majority of cases are sporadic. In ~ 5 - 10% 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 urinary catecholamines. When those results are positive then imaging is performed to try and localise the tumour.

Adrenal

They most frequently arises from the

chromaffin cells of the adrenal medulla.

Extra adrenal locations

Approximately 10% of all pheochromocytomas are not located in the adrenal glands. Extraadrenal tumours are more likely to be malignant and metastasise 4.

They can be found along the sympathetic chain as well as in the urinary bladder and organ of Zuckerkandl. Thoracic paragangliomas are rare and only account for 1 - 2 % of all cases of pheochromocytoma.

Radiographic features

As a general rule tumours in the adrenal region tend to be large at presentation, usually larger than 3 cm, with an average size of ≈ 5 cm. When confined to the adrenal glands, and especially if suspected clinically the diagnosis is readily made. Small extra-adrenal tumours can however be a challenge to find. Overall 98% of tumours are in the abdomen, and 90% are confined to the adrenal glands 6.

It is also important to note that it is not possible to distinguish malignant from benign pheochromocytomas merely on the

direct appearance of the mass. Rather, the distinction is made on demonstrating evidence of direct tumour invasion into adjacent organs / structures or the presence of metastases 4.

CT

CT is the first imaging modality to be used, with an overall sensitivity of 89%. This is on account of 98% of tumours being located within the abdomen and 90% limited to the adrenal glands 6.

On CT pheochromocytomas are large usually heterogeneous masses with areas of necrosis and cystic change.

Up to 7% demonstrate areas of calcification 4.

It should be noted, that in patients with suspected phaeochromocytomas contrast may be contraindicated as it could precipitate a hypertensive crisis.

MRI

MRI is the most sensitive modality for identification of pheochromocytomas, and is particularly useful in cases of extra-adrenal location. The overall sensitivity is said to be