Neurogenic tumours
.pdfNeurogenic tumours
Neurogenic tumours are the cause of approximately 90% of posterior mediastinal masses. They can be subdivided into three groups by their location and involvement of peripheral nerves or sympathetic chain.
1.peripheral nerve sheath tumour
2.sympathetic ganglia tumour
3.paraganglioma
Peripheral nerve sheath tumours and paragangliomas are far more common in adults while the sympathetic ganglia tumours are commoner in children.
Peripheral nerve sheath tumours
These tumours manifest as round paravertebral masses that span one or two vertebral bodies. They are homogenous, soft-tissue attenuation masses at CT and the commonest cause of posterior mediastinal and paravertebral masses. They may cause widening of the neural foramen and thickening of the adjacent posterior rib.
•schwannoma
•neurofibroma
•malignant peripheral nerve sheath tumour
Schwannoma and neurofibroma are by far the commonest type of neurogenic tumour in adults.
Sympathetic ganglia tumours
These tumours tend to present as elongated paraspinal masses that span multiple vertebral levels. Intra-tumoural calcification is common.
•neuroblastoma - young children
•ganglioneuroblastoma - older children
•ganglioneuroma - children and adults Neuroblastoma and ganglioneuroblastoma are most commonly seen in children and in a child they comprise the commonest neurogenic tumour.
Paraganglioma
These tumours are similar histologically to phaeochromocytoma and can be functioning or non-functioning.
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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 :
•~ 10% are extra-adrenal
•~ 10% are bilateral
•~ 10% are found in children
•~ 10% are familial
•~ 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.
Pathology |
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Pheochromocytomas |
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a type |
of paraganglioma. |
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Location |
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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 98% 6.
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T1 |
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slightly hypointense to the remainder of |
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the adrenal |
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if necrotic and / or haemorrhagic then |
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signal will be more heterogeneous |
T2 |
◦markedly hyperintense - this is a helpful
feature
◦ 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.
Neuroblastoma
A neuroblastoma is a tumour of neuroblastic origin and the most common extracranial solid childhood malignancies and the third commonest childhood tumor after leukemia and brain malignancies. It accounts for ~ 15% of childhood cancer deaths 2.
Epidemiology
The tumours typically occur in infants and very young children (mean age of presentation being ≈ 22 months) with 95% of cases diagnosed before the age of 10 years. Occasionally, they may be identified antenatally or immediately at birth (see congenital neuroblastoma) 2.
Clinical presentation
Clinical presentation is typically with pain or a palpable mass and abdominal distension, although numerous other presentations are encountered due to local mass effect.
Bony metastases may present with skeletal pain or a palpable lump or mass. Limping and irritability due to skeletal metastases is known