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1、Overview of CSF production The choroid plexuses are the source of approximately 80% of the CSF The blood vessels in the subependymal regions, and pia also contribute to the formation of CSF第1页/共38页Overview of CSF circulation The CSF flows from the lateral ventricles downward to the foramina of Magen

2、die and Luschka, to the perimedullary and perispinal subarachnoid spaces, and then upward to the basal cistern and finally to the superior and lateral surfaces of the cerebral hemispheres第2页/共38页CSF circulation The pressure gradient is highest in the lateral ventricles and diminishes successively al

3、ong the subarachnoid space Arterial pulsations in the choroid plexuses help drive the fluid from the ventricular system Normally, the periventricular tissues offer little resistance to the flow of CSF+-第3页/共38页CSF pressure The CSF volume and pressure are maintained on a minute to minute basis by the

4、 systemic circulation CSF pressure is in equilibrium with capillary pressure (determined by the arteriolar tone) An increase in blood PCO2 (hypoventilation) decreases pH and arteriolar resistance, this in turn gives rise to increased CSF pressure by increasing cerebral blood flow Hyperventilation ha

5、s the opposite effect第4页/共38页CSF pressure Normal intracranial pressure (ICP) in an adult is between 2-8 mmHg. Levels up to 16 mmHg are considered normal ICP higher than 40 mmHg or lower BP may combine to cause ischemic damage第5页/共38页CSF pressure Increased venous pressure has a direct effect on CSF p

6、ressure Downstream block of venous flow increases the volume of cerebral veins, dural sinuses, and the subarachnoid space第6页/共38页The function of the CSF The CSF acts as a “water jacket” for the brain and spinal cord The 1300 g adult brain weighs approximately 45 g when suspended in CSF第7页/共38页The fu

7、nction of the CSF The CSF acts like a “sink”, effectively flushing waste products as new fluid is secreted reabsorbed A constant CSF electrolyte composition helps maintain a stable medium for excitable cells (neurons)第8页/共38页Mechanisms of increase intracranial pressure Brain, Blood and CSF are held

8、in an inelastic container (cranium, vertebral canal and dura) Changes in volume of either element (Brain,CSF, Blood) is at the expense of the other two 第9页/共38页HydrocephalusCommunicating vs. Non-communicating (Dandy) This is an old classification of hydrocephalus The terms refer to the presence or a

9、bsence of a communication of the lateral ventricles with the spinal subarachnoid space第10页/共38页Communicating vs. Non-communicating This classification was based on the imaging findings after injection of dye into the ventricular system and simultaneous injection of air into the subarachnoid space Di

10、ffusion of dye into the subarachnoid space and passage of air into the ventricular space were the criteria for communicating hydrocephalus 第11页/共38页Non-communicating hydrocephalusThere is no communication between the ventricular system and the subarachnoid space. The commonest cause of this category

11、 is aqueduct blockage or stenosis. 第12页/共38页Aqueductal stenosis T h e n o r m a l a q u e d u c t measures about 1 mm in diameter, and is about 11 mm in length.第13页/共38页Aqueductal stenosis Is the most common cause of congenital hydrocephalus(43%) Aqueduct develops about the 6th week of gestation M:F

12、 = 2:1 Other congenital anomalies (16%): thumb deformities Prognosis: 11-30% mortality 第14页/共38页Etiology of aqueductal stenosis Intrinsic Pathology of the Aqueduct Septum or Membrane Formation: A thin membrane of neuroglia may occlude the aqueduct. It commonly occurs caudally. There may be a primary

13、 developmental defect or it may follow granular ependymitis from intrauterine infections. This is the rarest of the types of narrowing. Forking of the Aqueduct:Typically, there are two channels seen in midsagittal plane unable to handle CSF volume. Most often seen with spina bifida. Gliosis of the A

14、queduct: Usually of infectious origin showing a marked gliofibrillary response. The lumen is devoid of ependyma. Stenosis of the Aqueduct: Narrowed aqueduct without evidence of gliosis. This may have hereditary basis.第15页/共38页Etiology of aqueductal stenosis Extrinsic Pathology of the Aqueduct: Infec

15、tious. Abscesses. Neoplastic. Pineal tumors, brainstem gliomas, medulloblastoma, ependymoma. Vascular. AVM, aneurysm, Galen aneurysm. Developmental. Arachnoid cysts.第16页/共38页Clinical features of aqueductal stenosis O b s t r u c t i v e h y d r o c e p h a l u s : p r e s e n t s w i t h m a c r o c

16、 e p h a l y and/or intracranial hypertension. Parinauds syndrome. Inability to elevate eyes Colliers sign. Retraction of the eyelids第17页/共38页Imaging of aqueductal stenosis Ultrasonography c a n d e t e c t a q u e d u c t a l stenosis in utero.Sonogram第18页/共38页Imaging of aqueductal stenosis CT and

17、MRI. MRI i s e s s e n t i a l i f third ventriculostomy is to be considered.第19页/共38页Treatment of aqueductal stenosis T r e a t m e n t a n d Results Remove underlying cause of obstruction if possible. Third ventriculostomy as initial treatment of choice. V P s h u n t i f t e c h n i c a l reasons

18、 do not allow third ventriculostomy or if the c h i l d f a i l s a f t e r ventriculostomy. Aqueductal stent can be p l a c e d i f t e c h n i c a l l y feasible. Usually rarely done due to risk of upper brain stem injury.第20页/共38页Communicating hydrocephalus In communicating or non-obstructive hyd

19、rocephalus there is communication between the ventricular system and the subarachnoid space. The commonest cause of this group is post-infectious and post-hemorrhagic hydrocephalus. 第21页/共38页Causes of communicating hydrocephalus Overproduction of CSF Blockage of CSF circulation Blockage of CSF resor

20、ption Hydrocephalus ex-vacuo Normal pressure hydrocephalus第22页/共38页Overproduction of CSF Excessive secretion of CSF by the choroid plexus as in cases of choroid plexus papilloma or carcinoma. This is a rare cause. 第23页/共38页Blockage of CSF circulation This could be at any level of the CSF circulation

21、. It could be at the level of the foramen of Monro, with either unilateral or bilateral occlusion of the foramen of Monro giving dilatation of one or both lateral ventricles. This is commonly seen in the colloid cyst and tumors of the third ventricle. 第24页/共38页Dandy Walker Syndrome A common cause of

22、 obstructive hydrocephalus is Dandy Walker Syndrome where there is blockage of foramina of the 4th ventricle. This is a congenital condition associated with agenesis of the cerebellar vermis第25页/共38页Blockage of CSF resorption Poor resorption of CSF into the venous sinuses caused by scarring of the a

23、rachnoid villi and is commonly seen after meningitis or hemorrhage第26页/共38页Hydrocephalus Ex Vacuo Hydrocephalus ex-vacuo involves the presence of too much CSF, although the CSF pressure itself is normal. This condition occurs when there is damage to the brain caused by stroke or other form of injury

24、 or chronic neurodegeneration, and there may be an actual shrinkage of brain substance. 第27页/共38页Normal pressure hydrocephalus Normal pressure hydrocephalus (NPH) is usually due to a gradual blockage of the CSF drainage pathways in the brain. NPH is an unusual cause of dementia, which can occur as a

25、 complication of brain infection or bleeding (hemorrhage).第28页/共38页Normal pressure hydrocephalus In some patients, no predisposing cause can be identified. In patients with NPH, although the ventricles enlarge, the pressure of the CSF remains within normal range. NPH is characterized by gradual memo

26、ry loss (dementia), balance disorder (ataxia), urine incontinence, and a general slowing of activity. Symptoms progressively worsen over weeks. In some patients, an improvement of symptoms is noted immediately after the removal of spinal fluid with a lumbar procedure.第29页/共38页Treatment of hydrocepha

27、lus The two most commonly used shunt systems are the ventriculoatrial (VA) and ventriculoperitoneal (VP) shunts. The VP shunt is most commonly used as it is simpler to place, extra tubing may be placed in the peritoneum and the consequences of infection are less. 第30页/共38页Treatment of hydrocephalus

28、The VA shunt must be accurately located in the atrium and requires frequent revisions as the child grows to maintain the proper position of the distal end. In addition, infection is a more serious complication with a VA shunt as its location in the blood stream may lead to sepsis. 第31页/共38页Treatment

29、 of hydrocephalus Recently, in situations where both the abdomen and vascular system can no longer function to absorb CSF, Pediatric Neurosurgeons have begun to place the distal catheter in the pleural space (V-PL shunt). The distal catheter is placed through a small incision in the anterior chest w

30、all. As with the peritoneal shunt, extra tubing can be placed, reducing the need for further shunt revisions. 第32页/共38页Treatment of hydrocephalus Shunt systems include three components: (1) a ventricular catheter, (2) a one way valve and (3) a distal catheter. The ventricular catheter is a straight

31、piece of tubing, closed on the proximal end and usually with multiple holes for the entry of CSF along the proximal two centimeters of the tube. 第33页/共38页Treatment of hydrocephalus Shunts are composed of a material called Silastic. Silastic is made from a family of polymerized organic compounds term

32、ed silicone. Silicone is the substance that has caused controversy in breast implants because of the association with auto immune disorders. So far no cases of auto immune disease have been linked to the Silastic used in shunts. 第34页/共38页Treatment of hydrocephalus The most common sites for entry of

33、the ventricular catheter are a frontal position in line with the pupil at the coronal suture, a parietal position just above and behind the ear, or an occipital position three centimeters off the posterior midline. The position used varies with the configuration of the ventricles, the shape and size of the head and the surgeons preference. 第35页/共38页Shunt