Accumulation of extracellular fluid increases brain volume and then intracranial pressure causing the symptoms of cerebral edema.There are several clinical conditions in which vasogenic edema is present:

CNS tumors, like glioblastoma and meningioma
Infections like meningitis, abscess, and encephalitis
Inflammatory central nervous system disease such as multiple sclerosis
Brain hemorrhage
Traumatic brain injuries can lead to increased intracranial pressure, local damage, reduced cerebral blood flow, and focal ischemia secondary to vasogenic edema. Late stage of ischemic stroke after rapid recovery from cytotoxic edema
Hypertensive encephalopathy
Radiation injury

Ionic (Osmotic)
In ionic edema, the solute concentration (osmolality) of the brain exceeds that of the plasma and the abnormal pressure gradient leads to accumulation of water intake into the brain parenchyma through the process of osmosis. The blood-brain barrier is intact and maintains the osmotic gradient.The solute concentration of the blood plasma can be diluted by several mechanisms:

Improper administration of intravenous fluids, isotonic or hypotonic. Excessive water intake, syndrome of inappropriate antidiuretic hormone (SIADH). Rapid reduction of blood glucose in diabetic ketoacidosis or hyperosmolar hyperglycemic state. Hemodialysis has been associated with ionic edema and cellular swelling. Cerebral edema is a potentially life threatening complication of severely decreased sodium ion concentration in the blood (hyponatremia).Ionic brain edema can also occur around the sites of brain hemorrhages, infarcts, or contusions due to a local plasma osmolality pressure gradient when compared to the high osmolality in the affected tissue. Interstitial (hydrocephalic)
Interstitial edema can be best characterized by in noncomunnicating hydrocephalus where there is an obstruction to the outflow of cerebrospinal fluid within the ventricular system.
Sciatica can be caused by tumors impinging on the spinal cord or the nerve roots. Severe back pain extending to the hips and feet, loss of bladder or bowel control, or muscle weakness may result from spinal tumors or cauda equina syndrome. Trauma to the spine, such as from a car accident or hard fall onto the heel or buttocks, may also lead to sciatica. A relationship has been proposed with a latent Cutibacterium acnes infection in the intervertebral discs, but the role it plays is not yet clear. Pathophysiology
Sciatica is generally caused by the compression of lumbar nerves L4 or L5 or sacral nerve S1. Less commonly, sacral nerves S2 or S3 or compression of the sciatic nerve itself may cause sciatica. In 90% of sciatica cases, this can occur as a result of a spinal disc bulge or herniation. Intervertebral spinal discs consist of an outer anulus fibrosus and an inner nucleus pulposus. The anulus fibrosus forms a rigid ring around the nucleus pulposus early in human development, and the gelatinous contents of the nucleus pulposus are thus contained within the disc. Discs separate the spinal vertebrae, thereby increasing spinal stability and allowing nerve roots to properly exit through the spaces between the vertebrae from the spinal cord. As an individual ages, the anulus fibrosus weakens and becomes less rigid, making it at greater risk for tear.