Brain Tumors (Lec 7) PDF

Systematic Approach to Brain Tumors Dr R. Golamaully. Imaging Modalities Incidence of CNS tumors Roughly 1/3 of CNS tumors are metastatic lesions, 1/3 - gliomas and 1/3 - non-glial origin. Glioma is a non-specific term indicating that the tumor originates from glial cells lik...

Systematic Approach to Brain Tumors Dr R. Golamaully. Imaging Modalities Incidence of CNS tumors Roughly 1/3 of CNS tumors are metastatic lesions, 1/3 - gliomas and 1/3 - non-glial origin. Glioma is a non-specific term indicating that the tumor originates from glial cells like astrocytes, oligodendrocytes, ependymal and choroid plexus cells. Astrocytoma is the most common glioma and can be subdivided into the o low-grade pilocytic type, o the intermediate anaplastic type and o the high grade malignant glioblastoma multiforme (GBM). GBM is the most common type (50% of all astrocytomas). The non-glial cel tumors are a large heterogenous group of tumors of which meningioma is the most common.  In adults about 50% of all CNS lesions are Age distribution metastases. The age of the patient is an important factor for the differential diagnosis. Other common tumors in adults are astrocytomas, glioblastoma multiforme, meningiomas, Specific tumors occur < age of 2, like choroid oligodendrogliomas, pituitary adenomas and plexus papillomas, anaplastic astrocytomas schwannomas. and teratomas. In the first decade medulloblastomas, Astrocytomas occur at any age, but glioblastoma astrocytomas, ependymomas, multiforme is mostly seen in older people. craniopharyngeomas and gliomas are most common, while metastases are very rare. When they do occur at this age, metastases of a neuroblastoma are the most frequent. Although cancer is rare in children, brain tumors are the most common type of childhood cancer after leukemia and lymphoma. Most of the tumors in children are located infratentorially. Tumor spread Intra- v/s Extra-axial extra-axial, then the lesion is not actually a in an adult - metastasis or brain tumor, but derived from the lining of astrocytoma in 75% of cases. the brain or surrounding structures 80% - meningioma or a schwannoma. The T2W-images - schwannoma located in the cerebellopontine angle (CPA). Typical signs of an extra-axial tumor. o There is a CSF cleft (yellow arrow). o The subarachnoid vessels that run on the surface of the brain are displaced by the lesion (blue arrow). o There is gray matter between the lesion and the white matter (curved red arrow). o The subarachnoid space is widened because growth of an extra-axial lesion tends to push away the brain. All these signs indicate that this is a typical extra- axial tumor. In the region of the CPA 90% of the extra-axial tumors are schwannomas – acoustic neuroma  Another sign of an extra-axial origin is a broad dural base or a dural tail of enhancement as is typically seen in meningiomas. Another sign of an extra-axial origin are bony changes. Bony changes are seen in bone tumors like chordomas, chondrosarcomas and metastases. They can also be secondary, as is seen in meningiomas and other tumors. a meningioma with a broad dural base and a dural Extra-axial tumors are not tail of enhancement derived from brain tissue and do not have a blood-brain- hyperostosis in the adjacent bone and the lesion barrier, so most of them enhances homogeneously. enhance homogeneously.  Intra- vs Extra-axial … ?? falcine meningioma, i.e. extra-axial However, there is gray matter on the.anteromedial and posteromedial side of the lesion (red arrow). This indicates that the lesion is intra-axial. If the lesion was extra-axial the gray matter should have been pushed away. This proved to be a melanoma metastasis Local tumor spread o Astrocytomas spread along the white matter tracts and do not respect the bounderies of the lobes. Because of this infiltrative growth, in many cases the tumor is actually larger than can be depicted with MR. o Ependymomas of the 4th ventricle in children tend to extend through the foramen of Magendie to the cisterna magna and through the lateral foramina of Luschka to the cerebellopontine angle. o Oligodendrogliomas typically show extension to the cortex. Ependymoma with extension to the prepontine area (blue arrows) and into the foramen magnum (red arrow). Subarachnoid seeding Some tumors show subarachnoid seeding and form tumoral nodules along the brain and spinal cord. Primitive neuroectodermal tumor (PNET), ependymomas, GBMs, lymphomas, oligodendrogliomas and choroid plexus papillomas. Medulloblastoma with leptomeningeal seeding  One of the most important roles of imaging is to assess the extent of a tumor. A patient who presented with multiple cranial nerve abnormalities. o extra-axial tumor in the region of the left cavernous sinus. o Homogeneous enhancement with a broad dural tail. This is typical for a meningioma. The actual extent of the tumor is greater than expected. o The tumor is situated in the pterygopalatine fossa and extends into the orbit. o It also spreads anteriorly into the middle cranial fossa Local tumor spread Another … important consideration is the effect on the surrounding structures. Primary brain tumors are derived from brain cells and often have less mass effect for their size than you would expect, due to their infiltrative growth. This is not the case with metastases and extra- axial tumors like meningiomas or schwannomas, which have more mass effect due to their expansive growth. diffusely infiltrating intra-axial tumor occupying most of the right hemisphere with only a minimal mass effect. This is typical for the infiltrative growth seen in primary brain tumors. There is no enhancement so this would probably be a low-grade astrocytoma. Midline crossing The ability of tumors to cross the midline limits the differential diagnosis. o Glioblastoma multiforme (GBM) frequently crosses the midline by infiltrating the white matter tracts of the corpus callosum. o Radiation necrosis can look like recurrent GBM and can sometimes cross the midline. o Meningioma is an extra-axial tumor and can spread along the meninges to the contralateral side. o Lymphoma is usually located near the midline. o Epidermoid cysts can cross the midline via the subarachnoid space. o Multiple Sclerosis can also present as a mass lesion in the corpus callosum. Multifocal disease Multiple tumors in the brain usually indicate metastatic disease Primary brain tumors are typically seen in a single region, but some brain tumors like lymphomas, multicentric glioblastomas and gliomatosis cerebri can be multifocal. Some tumors can be multifocal as a result of seeding metastases: this can occur in medulloblastomas (PNET-MB), ependymomas, GBMs and oligodendrogliomas. Metastases Multiple meningiomas and a schwannoma in a patient Meningiomas and schwannomas can be with Neurofibromatosis II multiple, especially in neurofibromatosis type II. Multiple brain tumors can be seen in phacomatoses: o Neurofibromatosis I: optic gliomas and astrocytomas o Neurofibromatosis II: meningiomas, ependymomas, choroid plexus papillomas o Tuberous Sclerosis: subependymal tubers, intraventricular giant cell astrocytomas, ependymomas o von Hippel Lindau: hemangioblastomas Diffusion weighted imaging Normally water protons have the ability to diffuse extracellularly and loose signal. High intensity on DWI indicates restriction of the ability of water protons to diffuse extracellularly. Restricted diffusion is seen in abscesses, epidermoid cysts and acute infarction (due to cytotoxic edema). In cerebral abscesses the diffusion is probably restricted due to the viscosity of pus, resulting in a high signal on DWI. In most tumors there is no restricted diffusion - even in necrotic or cystic components. This results in a normal, low signal on DWI.  Blood brain barrier The brain has a unique triple layered blood- brain barrier (BBB) with tight endothelial junctions in order to maintain a consistent internal milieu. Contrast will not leak into the brain unless this barrier is damaged. Enhancement is seen when a CNS tumor destroys the BBB. Extra-axial tumors such as meningiomas and Some non-tumoral lesions enhance because schwannomas are not derived from brain they can also break down the BBB and may cells and do not have a blood-brain barrier. simulate a brain tumor. Therefore they will enhance. These lesions include like infections, demyelinating diseases (MS) and infarctions. There is also no blood-brain barrier in the pituitary, pineal and choroid plexus regions. Thank you