Discussing physiology and neuroanatomy of cerebrospinal fluid and pathophysiology of hydrocephalus for USMLE Step 1. Conditions covered are hydrocephalus, communicating hydrocephalus, noncommunicating hydrocephalus, hydrocephalus ex-vacuo and normal pressure hydrocephalus.
ANATOMY AND PHYSIOLOGY OF CSF FLUID
Begins with the lateral ventricles located above the thalamus. This continues as the third ventricle, cerebral aqueduct, fourth ventricle and then goes into spinal cord. The lateral ventircle is located in telencephalon. The third ventricle is in the diecephalon. The cerebral aqueduct is in the midbrain. The fourth ventricle which is found in mesecephalon.
Above the fourth ventricle is the corpus collosum and divided by the septum pellucidum. And below is the caudate nucleus. The cerebellum encompasses the pons and medulla.
The entire brain and spinal is surrounded by subarachnoid space. The dura mater is surround the arachnoid mater which, but there are certain areas where it creates sinus, such as superior saggital sinus. There are a few foramens such as the foramen of Monroe or interventricular foramen. The cerebral aqueduct and finally in the fourth ventricle you have the foramen of lushka and foramen of Magenda.
The cerebral spinal fluid is produced by the ependymal cells called the . The fluid goes through the lateral ventricle, then the third ventricle, then the cerebral aqueduct, the fourth ventricle. It goes through the foramen of lushka into the pontine cistern. Foramen of magenda goes into the cistern magna. From there it goes into the spinal cord and goes up towards to the cerebellar area. Here there are arachnoid granulation that go through the superior saggital sinus and goes to the venous blood.
HYDROCEPHALUS
Hydrocephalus is any condition that leads to increase CSF fluid.
Increase production is one cause however it is very rare. The only cause can be a tumor of the choroid plexus.
Circulation can be two types such as communication and non-communicating. Noncommunicating means that the problem is before the foramen of lushka and magenda. This can be found in a cyst in the foramen of Monroe which will block the flow and cause enlargement of the area. Cerebral aqueduct can be caused by congenital stenosis. And cerebellar tumors which compress the foramen of lushka and magenda.
Communicating causes means there is a problem in the subarachnoid space. Arachnoid stricture post meningitis is one common cause.
Decrease drainage is focusing on the arachnoid granulation which may become clogged and then the fluid can't drain into superior saggital sinus and can't go into the venous fluid.
Normal pressure hydrocephalus is when the brain accomodates the increase spinal fluid by compressing itself. Therefore there is increased CSF but no increase pressure. Leads to the 3W symptoms. Wacky, wobbly, wet. Dementia, gait, urinary incontinence are the three primary symptoms of normal pressure hydrocephalus.
HYDROCEPHALUS EX-VACUO
Atrophy causes increase CSF to take up the extra space. This hydrocephalus can be caused by alzheimer, huntington, and psuedotumor creberi