Medical Imaging of Intracranial Tumors

Abstract

The intracranial tumors can be divided into three categories according to the location of tumor growth: (1) Intra-axial tumors, including astrocytic tumors, medulloblastoma, lymphomas, hemangioma, and metastasis. (2) Intraventricular tumors, tumors arising from the ventricular wall, such as ependymoma, tumor arising from choroid plexus, such as papilloma and meningioma. (3) Extra-axial tumors, such as meningioma, pituitary adenoma, and schwannoma. The names of the intracranial tumors using 2016 WHO CNS tumor classification. The diagnosis of intracranial tumors is mainly based on CT and MRI imaging features. Some tumors have specific anatomical locations, and some tumors have specific clinical symptoms. New MRI technologies such as DWI and ADC, and the use of MRS, provide valuable assistance in the diagnosis of CNS tumors. Based on the above, 70–80% of the tumor diagnosis of intracranial tumors using CT and MRI can be consistent with surgery and pathology, and the other 20–30% need to wait for the pathological examination. Low-grade astrocytomas showed changes in the density and signal intensity of the brain tissue on CT and MRI; the BBB is not damaged, so the contrast agent does not enhance it. Glioblastoma is irregular in shape, severely central necrosis, cauliflower-like shape, and usually large of tumor size. Medulloblastoma is common in children; most of them grow in the cerebellar vermis, which will compress the fourth ventricle and aqueduct and cause hydrocephalus. Lymphoma is often multiple and less necrosis, with higher DWI signals and more elevated MRS lipids. Metastases may be intra-axial, extra-axial, or even in the skull, and some are leptomeningeal metastases. Hemangioblastomas may have a mural nodular sign; solid hemangioblastoma shows hypointensity on DWI due to high vascularity; this is a characteristic sign. Meningiomas are always solid; less cystic change and may have calcifications, hyperostosis of the adjacent skull, and “dural tail sign” seen in MRI. If the tumor has central necrosis and adjacent bone erosion, it is atypical or anaplastic meningioma. Pituitary adenomas are in the sella turcica, and may extend upward to compress the optic chiasm, and are very easy to diagnose using CT or MRI. But functional microadenoma needs coronal section and contrast enhancement to see the delayed enhancement at the microadenoma. The acoustic neuroma is the highest incidence of cranial nerve schwannomas. The tumor grows in the CP angle cistern and will extend into the internal auditory canal, to form a “fruit stalk sign.” Germ cell tumors display a characteristic of growing in the midline, such as the pineal region and suprasellar region.