generic and comprehensive term that includes, from the neuroradiological point of view, all the neoplasias that involve the brain, and not only those originating from the brain tissue or structure.
Many classifications have been proposed for brain tumours (Table 1), mainly based on histological staining and type of cell from which the tumour originates.
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| | Embryonal tumours | | | | | | Neuroblastoma | | | | | Retinoblastoma | | | | | Primitive neuroectodermal tumours (PNET) | | | | | | Medulloblastoma (posterior fossa PNET or PNET-MB) | | | | | Cerebral/spinal PNET | | | Cranial and spinal nerve tumours | | | | | | Schwannoma (neurinoma or neurilemmoma) | | | | | Neurofibroma | | | | | Malignant peripheral nerve sheath tumours (MP-NSTs) | | | | Haemopoietic neoplasms | | | | | | Lymphoma | | | | | Leukaemia (granulocytic sarcoma or "chloroma" | | | | | Plasmacytoma | | | | Pituitary tumours | | | | | Cysts and tumour-like lesions | | | | | | Rathkes cleft cyst | | | | | Dermoid cyst | | | | | Epidermoid cyst | | | | | Colloid cyst | | | | | Enterogenous cyst | | | | | Neuroglial cyst | | | | | Lipoma CNS | | | From the point of view of the neuroradiological diagnosis, attention should be focused primarily on some major questions that should be answered, in the interest of the best clinical management of the patient, such as:
Is there a lesion?
Is the space-occupying lesion a tumour, in the sense of a neoplasia, or is it non-neoplastic (abscess, cyst, haemorrhage, etc.)?
Where is it located (intra-axial, extra-axial, intraventricular, originating from dura, bone, at the base of the skull, at the vault, on the midine, etc.) (see intra axial tumour, extra axial brain tumour, skull base tumour of)?
What is its macroscopic structure (solid, cystic, mixed, haemorrhagic, with calcifications, highly vascularized, etc)?
What are its effects on the surrounding structures (infiltration, compression, dislocation, encasement of vessels, etc.)?
Is it single or multiple?
Is it primary or metastatic?
All these questions can now be answered relatively easily from the neuropathological and neuroanatomical knowledge provided by MR and CT since imaging abnormalities closely reflect pathological changes. Angiography is nowadays only rarely needed for diagnosis.
The incidence of primary intracranial tumours in the US is approximately 4,5 per 100,000 people and it is estimated that about 15,000 new cases are diagnosed every year.
About 80-85% of all intracranial tumours occur in adults, the majority of which are situated in the supratentorial compartment. In the adult, the most common intra-axial supratentorial neoplasm is the glioblastoma (see Glioblastoma multiforme), while metastasis is the most common intra-axial tumour of the posterior fossa. In the paediatric population, the CNS is the second most common site of paediatric neoplasia. Excluding the first year of life and adolescence, the location of intracranial tumours in the paediatric age group is infratentorial in 60-70% of cases, of which 75% involve the cerebellum and 25% reside in the brain stem. Nearly all of these lesions are primary CNS tumours, but the spectrum of histology differs remarkably from that seen in adults (Table 2).
Brain tumour, Table 2 a. Brain tumour in children less than two years of age.
Brain tumour, Table 2 b. Brain tumours in children.
(Data from: Harwood-Nash DC: Primary neoplasms of the central nervous system in children, Cancer 67:1223;1223-1228, 1991.)
A macroscopic radiological appearance of a brain tumour may vary tremendously according to size, histology and location. The very early intra-axial tumour may be barely detected as a faint T2 hyperintensity on MR and be completely missed on CT, in an adult patient with the first seizure of his life. A glioblastoma may present as a large space-occupying lesion with haemorrhages and necrosis; haemorrhage may, however, be encountered also in benign tumours such as neurinomas or pituitary adenomas (see intratumoral haemorrhage). Some tumours are completely solid, others are mainly cystic, such as pilocytic Astrocytomas or craniopharyngiomas.
Calcifications may be found in meningiomas, craniopharyngiomas, ependymomas. Some lesions have a unique appearance, such as Lipoma CNS or epidermoid tumour. GS |