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Normal pressure hydrocephalus

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Normal pressure hydrocephalus

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Normal pressure hydrocephalus

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A 73-year-old man comes to the physician due to difficulty walking. The patient describes his gait as though his feet are “glued to the ground.” Additionally, he has been having difficulty finishing his daily crossword puzzle, which he attributes to impaired concentration. He has not experienced headaches, nausea, vomiting, or visual changes, but he has experienced episodes during which he has a sudden urge to urinate. The patient frequently has difficulty making it to the bathroom due to his gait dysfunction. Past medical history is notable for a subarachnoid hemorrhage that occurred several years ago. Vital signs are within normal limits. The patient’s Mini-Mental Status Examination score is 22/30 (normal: ≥ 24). Physical examination is notable for a broad-based and shuffling gait. Which of the following is the most likely cause of this patient’s symptoms?

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Transcript

In normal pressure hydrocephalus, hydrocephalus can be broken down into “hydro” which means water and “cephalus” which means head.

Hydrocephalus, which is also termed as “water on the brain”, is an excessive buildup of cerebrospinal fluid within the brain.

Even though the pressure on lumbar puncture is expected to be increased, in this case, it’s normal, which is why it’s termed as “normal pressure” hydrocephalus.

Let's start with some relevant anatomy. The brain has four interconnected cavities in the brain called ventricles, and each one contains a structure called a choroid plexus.

The choroid plexus is made up of ependymal cells which produces cerebrospinal fluid - a fluid that helps provide buoyancy and protection, as well as metabolic fuel for the brain.

Highest up, are two C-shaped lateral ventricles that lie deep in each cerebral hemisphere.

The two lateral ventricles drain their cerebrospinal fluid into the third ventricle, which is a narrow, funnel-shaped, cavity at the center of the brain.

The third ventricle makes a bit more cerebrospinal fluid and then sends all of the cerebrospinal fluid to the fourth ventricle via the cerebral aqueduct.

The fourth ventricle is a tent-shaped cavity located between the brainstem and the cerebellum.

After the fourth ventricle, the cerebrospinal fluid enters the subarachnoid space, which is the space between the two inner linings of the brain - the arachnoid and pia mater.

Now, the arachnoid mater protrudes into the outermost covering, called dura mater, at various points.

It looks a bit like little fingers poking through, and these protrusions are called arachnoid granulations.

Cerebrospinal fluid makes its way through these arachnoid granulations and gets into the dural sinus which is filled with venous blood and is on the other side of the arachnoid granulation.

The pressure within the subarachnoid space is higher than the pressure in the dural sinus, so CSF flows through the arachnoid granulations is only in one direction.

Normal pressure hydrocephalus develops when cerebrospinal fluid is unable to get through those arachnoid granulations normally.

This process develops gradually and most commonly affects the elderly.

There are two types of normal pressure hydrocephalus.

The first type is an primary normal pressure hydrocephalus, where the cause is idiopathic or unknown.

The second type is secondary normal pressure hydrocephalus, where the cause is damage to the arachnoid villi which disrupts CSF reabsorption.

Some known causes of arachnoid villi damage are a subarachnoid hemorrhage and meningitis, both of which cause a tremendous amount of inflammation to the protective layers of the brain.

Summary

Normal pressure hydrocephalus is a condition characterized by ventricular enlargement, without an increase in cerebrospinal fluid pressure on lumbar puncture. Cerebrospinal fluid (CSF) accumulates slowly and gradually in the ventricles, causing them to dilate. Ventricular dilation restores the CSF pressure to the normal level, hence the normal findings on lumbar puncture.

People with normal pressure hydrocephalus present with urinary incontinence, gait disturbances, and dementia. The excess amount of CSF can be temporarily drained through a lumbar puncture, but the long-term management is a surgical procedure called a ventriculoperitoneal shunt, in which a tube is inserted into one of the ventricles of the brain and directed to the abdomen, where the excess CSF can be absorbed.

Sources
  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Reference ranges for fetal ventricular width: a non-normal approach" Ultrasound in Obstetrics and Gynecology (2007)
  6. "Fetal mild idiopathic lateral ventriculomegaly: is there a correlation with fetal trisomy?" Ultrasound in Obstetrics and Gynecology (1993)
  7. "Postnatal clinical and imaging follow-up of infants with prenatal isolated mild ventriculomegaly: a series of 101 cases" Pediatric Radiology (2007)