CSF Physiology and Hydrocephalus

• CSF volume is 150 cc (25 cc in ventricles); 450 cc is produced per day
• arachnoid granulations absorb if pressure is 3-6 cmH2O above venous pressure
• normal pressure is 10-15 cmH2O; 3-6 cmH2O in children; 20-30 cmH2O when sitting

• secretion increased by CO2 and volatile anesthetics; secretion decreased by NE and carbonic anhydrase inhibitors
• Hydrocephalus
• Defined as ventriculomegaly due to altered cerebrospinal fluid production, flow, or absorption
• Symptoms: Irritability, lethargy, poor feeding, more slowly attaining or losing milestones, vomiting
• Signs: Rapidly increasing head circumference, bulging anterior fontanelle, paralysis of upward gaze (Parinaud’s)
• Diagnosis: Skull films show split sutures
• Uncontrasted head CT shows ventricular enlargement
• Types:
• Communicating
• Obstruction of CSF flow in the subarachnoid cisterns or poor absorption at the Pacchinian granulations
• Ventricles are all large and communicate
• External
• Decompression of ventricles into subdural or subgaleal space
• Usually occurs postoperatively at surgical site
• Non-Communicating (Obstructive)
• Obstruction of CSF flow is within the ventricular system
• Normal pressure hydrocephalus
• Communicating form which arises typically in adults in face of ostensibly normal CSF pressure
• Hydrocephalus ex vacuo
• Ventricular enlargement which results from loss of brain parenchyma
• Etiology:
• Congenital – aqueductal stenosis, Dandy-Walker syndrome (small malformed cerebellum with large posterior fossa cyst in communication with 4^th ventricle obstructing flow of CSF to subarachnoid cisterns)
• Intracranial mass (especially posterior fossa, third ventricular and pineal region lesions)
• Subarachnoid inflammation – meningitis, hemorrhage
• Loss of brain parenchyma – infarcts, perinetal insults
• Treatment: Shunting of CSF
• Intraventricular Hemorrhage (IVH) – most common cause of congenital hydrocephalus
• Hemorrhage in the periventricular germinal matrix ruptures into the ventricular system
• Frequently seen in premature infants
• May proceed to cause non-obstructive hydrocephalus
• Grading:
• I – Isolated hemorrhage confined to the germinal matrices
• II – Intraventricular extension of germinal matrix hemorrhage without hydrocephalus
• III – Intraventricular extension of germinal matrix hemorrhage with accompanying ventricular enlargement
• IV – Intraparenchymal extension of hemorrhage in addition to intraventricular hemorrhage with hydrocephalus
• Diagnosis is made by head ultrasound
• Follow patient’s daily head circumference plotted on appropriate head growth chart
• Recommend head CT as soon as patient stable enough to obtain
• Treatment: VP shunt
• Infants <1500 g generally are too small for shunting, so serial LP’s are done until patient is large enough for shunting
• If LP’s unsuccessful, serial ventricular taps through the fontanelle can be performed or a temporary blind-ended ventricular catheter can be placed and serially tapped
• CSF Shunting
• Ventriculo-peritoneal (VP) – Most common shunt used today
• Drains fluid from ventricles to peritoneum
• Ventriculo-atrial (VA)/Ventriculo-jugular (VJ)
• Drains fluid from ventricles into venous system through the facial, jugular or subclavian vein
• Distal tubing on CSR should be between T4 and T8
• Lumbo-peritoneal (LP)
• Drains fluid from lumbar theca to peritoneum
• Only used in communicating hydrocephalus (NPH)
• Subdural-peritoneal
• Drains fluid from subdural space to peritoneum
• Used in chronic subdural hygroma/hematoma which recur after external drainage
• Shunt hardware
• Rickham Reservoir – Hard non-compressible plastic dome placed where ventricular catheter exits skull
• Site of shunt tap with a Huber needle
• Some older shunts do not have this reservoir
• Valve – Regulates intracranial run-off pressure; Are uni-directional allowing flow only distally; Many different types
• Holter – shaped like cylinder
• PS Medical – single compressible dome, available in low, medium and high pressure
• Delta – combined anti-syphon device and compressible dome, must be placed at ear level, available in 2 pressure levels designated I and II
• Can be “pumped” to assess shunt function – Should empty without resistance and refill rapidly
• Most are impregnated with radio-opaque arrow so that appropriate direction of flow and pressure setting can be confirmed on plain x-ray
• Single dot: PS Medical low pressure, Delta I
• Double dot: PS Medical medium pressure, Delta II
• Triple dot: PS Medical high pressure
• Distal “A” tubing – Travels subcutaneously to peritoneal cavity
• Needs to be lengthened when patient hits adolescent growth spurt
• Should be randomly coiled within abdomen
• Straight Metal Connectors
• Used to connect above pieces
• Potential site of shunt disconnection
• On-Off Valve
• Additional valve with on-off switch to allow control of shunt patency
• When central ball is depressed (dimpled), shunt is occluded
• “Y” Connector
• Y-shaped metal connector used to connect biventricular catheters to a single distal tubing
• Anti-Syphon Device
• Additional valve to prevent drainage of CSF during change in posture
• Used in patients who over-drain CSF and have slit ventricles
• Can also place catheter into ventricle leading to blind reservoir for CSF access for intrathecal chemotherapy (Ommaya), or into lumbar cistern for intrathecal morphine (leads to lumbar flushing reservoir on chest wall)
• Shunt Dysfunction
• Multiple etiologies:
• Proximal:
• Most common source of dysfunction
• Plugged ventricular/lumbar catheter
• Disconnection from Rickham reservoir
• Distal:
• Disconnection of tubing
• Broken valve
• Distal tubing no longer inside abdomen
• Abdominal loculation at tubing tip (CSFoma)
• Classic presentation: Headache, lethargy, nausea/vomiting
• Evaluating shunt function:
• Shunt series
• Plain x-rays of the entire system searching for disconnection, breaks, and tubing placement
• Skull films (AP, lat), CXR, KUB (and LS spine films for LP)
• All shunt components are radio-opaque except parts of some valves
• Uncontrasted head CT
• Most useful when used in comparison to prior films when shunt was working
• Evaluate ventricular size for enlargement
• Abdominal ultrasound/CT
• Used to evaluate patients with significant abdominal pain or distention
• Can reveal loculated fluid collections (CSFoma) in abdomen
• Shunt tap
• Placing Huber needle into Rickham reservoir and checking for spontaneous CSF flow and distal run-off
• Only to be done under the supervision of a neurosurgery resident
• Never go to sleep without fixing a broken shunt
• Shunt Infection
• Rarely occurs more than a few months after the last manipulation
• In patient with a fever, evaluate for other sources first unless there are clear meningeal signs
• Ask about recent viral illness in family
• Check urine, lungs, ears, throat
• Send appropriate cultures
• Low grade shunt infections may present only as a loculated CSFoma in abdomen
• If shunt is infected, it must be removed since it is a foreign body which serves as a continued nidus for infection
• Shunt dependent patients with infections are maintained with externalized ventricular catheters until infection clears and new shunt can be placed
• Intraventricular injection of antibiotics (either gent or vanco) is frequently used in addition to systemic antibiotics
• Normal Pressure Hydrocephalus (NPH) – symptomatic hydrocephalus without elevated ICP
• Symptoms: Classic triad – progressive dementia, urinary incontinence, and gait apraxia
• Etiology: Fibrosing arachnoiditis of unknown etiology, prior SAH, trauma, prior surgery, meningitis, idiopathic
• Idiopathic form typically presents in the 6^th decade with no sex predominance
• Diagnosis: Uncontrasted head Ct shows ventriculomegaly
• Nuclear cisternogram shows delayed reabsorption of CSF
• Treatment: VP/LP shunt
• Dementia responds least to treatment
• Pseudotumor Cerebri (Benign Intracranial Hypertension) – elevated ICP without hydrocephalus
• Symptoms: Headaches, papilledema, and increased intracranial pressure in the absence of CNS inflammatory disease, venous occlusion, or a space occupying mass
• Associated with obesity, pregnancy, and menstrual irregularities
• Presents typically in women during adolescence or early adulthood
• Diagnosis: Normal head CT (except decreased ventricular size)
• Increased ICP (measured by opening pressure on LP)
• Treatment:
• Medical therapy: Weight loss, Prednisone, Acetazolamide (carbonic anhydrase inhibitor that has a diurectic effect and decreases CSF production)
• Serial LP’s
• Surgery if symptoms are refractory or patient has progressive visual impairment
• Optic sheath decompression
• VP or LP shunt