Normal pressure hydrocephalus is a traffic hydrocephalus syndrome in which the ventricles are enlarged, although the cerebral crest fluid pressure is normal. It was first proposed by Adams and Hakim in 1965 and presents as a triad of gait difficulty, altered consciousness, and sphincter dysfunction (urinary incontinence) with ventricular dilatation and normal lumbar cerebral crest fluid pressure without optic papilloedema.
Gait instability is often the primary symptom, preceding other symptoms by months or years. In some patients, gait instability and mental changes may occur simultaneously or after other symptoms. The presentation ranges from mild instability to inability to walk or even to stand, and there is often a history of falls. The Romberg test shows swaying without cerebellar ataxia.
Mental retardation varies widely from patient to patient, with recent memory loss being the most obvious feature. Patients often show dullness, decreased spontaneous or active activity, diminished conversation, reading, writing, hobbies and creativity, lack of concern for family, indifference or apathy, isolation, and poor productivity. Some people refer to these complex activity abnormalities as loss of will personality. Some trials have found that patients largely retain the ability to use vocabulary, while using non-vocabulary use skills such as drawing, copying, arranging tables, and tests of difficult problems are largely impaired, and as the disease progresses, they are unresponsive to questions posed by those around them, give only brief or partial answers, and have slow or delayed autonomic activity.
In some patients with early intellectual impairment, there is anxiety and complex intellectual dysfunction, such as paranoia, fantasy and incoherence, and there may also be slow movement and rigidity, resembling Parkinson’s symptoms. Urinary incontinence is very urgent in some patients, but most patients exhibit hypoesthesia of urinary perception or urinary movements, and fecal incontinence is rare. The other category is sporadic with no obvious etiology. The main pathological changes of the disease are enlargement of the ventricular system, adhesions and occlusion of the subarachnoid space on the convex surface or floor of the brain. The most common etiology is subarachnoid hemorrhage, followed by intracranial tumors and also familial normal cranial pressure hydrocephalus.
Paget’s disease sometimes produces extensive subarachnoid obstruction of the subarachnoid space at the base of the brain. Meningeal infections, such as tuberculous meningitis, tend to produce arachnoid adhesions in the later stages of the lesion; traumatic subarachnoid hemorrhage and intracranial surgical bleeding into the subarachnoid space can produce hydrocephalus. Recently, it has been suggested that stenosis of the midbrain aqueduct is also a more common etiology.
A definitive diagnosis can usually be made based on the history, clinical manifestations, and imaging ancillary examinations.
Other ancillary examinations.
1, imaging examination: cranial CT examination is an important means of normal cranial pressure hydrocephalus examination, which can determine the degree of ventricular enlargement and cortical atrophy and the cause of hydrocephalus, and at the same time, it is also a means to observe the postoperative shunt effect and complications. The typical CT scan shows ventricular enlargement with no significant cortical atrophy, while MRI images can observe smaller intracranial lesions from sagittal, coronal and horizontal aspects and are superior to CT. Low signal changes in T1-weighted images around the ventricles can indicate a progressive trend of hydrocephalus.
2.Nuclide cerebral pool imaging: injected into the subarachnoid space by lumbar puncture with radionuclide, and observed by photographing the brain and ventricles as they enter. The most commonly used is iodine 131 labeled human serum protein (RISA), and recently indium-diethylaminepentaacetic acid (DTPA) is used as a marker, about 500UC is injected into the subarachnoid space and scanned at 4h, 24h, 48h and 72h for observation.
Three types of scans could be seen.
(1) Normal type: the radionuclide is in the convex surface of the brain and does not flow into the ventricles.
(2) Normal cranial pressure hydrocephalus: radionuclide enters the ventricles and stays there, and the convex surface of the brain cannot be shown for 72h.
(3) Mixed type: most patients have this type, i.e. both ventricles and convexity of the brain can be shown on staging scans. Since radionuclide scan has no definite relationship to judge the effect of shunt, this examination is not very helpful to evaluate normal cranial pressure hydrocephalus, and is not commonly used clinically at present.
3, other examinations: cranial plain film generally does not have chronic cranial hypertension signs; EEG can be seen persistent extensive slow waves; in patients with normal cranial pressure hydrocephalus 131 can show a reduction in cerebral blood flow, cerebral angiography lateral image can be seen in the anterior cerebral artery extraordinarily straight, the middle cerebral artery lateral cleft point outward displacement. In the presence of cerebral atrophy, the distance between the small vessels and the intracranial plate is widened in the capillary phase, and pneumoencephalography shows enlargement of all ventricles and different degrees of brain pools, which are no longer commonly used in the clinical examination of hydrocephalus.
Determination of shunt indications
(1) Evaluation of clinical symptoms.
Walking instability is an important indication to evaluate the effect of shunt. Those whose gait instability precedes mental retardation respond well to shunt surgery, while those whose mental retardation alone is the main symptom have a poor shunt effect. It has been suggested that 74% of those with walking instability recover after shunting and that walking instability is an essential condition for the indication of shunting for normal cranial pressure hydrocephalus, and 87,5% of patients have significant recovery of symptoms after shunting. Some authors have also taken ventricular enlargement and gait instability as the criteria for shunt, and 83% of the patients could achieve good results after shunt.
(2) Cranial pressure measurement.
Patients with normal cranial pressure hydrocephalus who have several lumbar puncture pressure measurements at the upper limit of normal value, and those who have fluctuating increase in cranial pressure after 24h continuous monitoring or those who have improvement in patient’s symptoms after lumbar puncture fluid release, have more obvious effect after shunt. There are reports that continuous monitoring of intracranial pressure with frequent B-wave activity and 24h B-wave activity of more than 50% can significantly improve the symptoms after shunt.
(3) Lumbar spine perfusion test.
A tee tube is connected to the lumbar puncture, and the two ends of the tube are connected to a pressure continuous tracer and a syringe, and saline is injected into the lumbar subarachnoid space at a rate 2 times the normal secretion of cerebral crest fluid (about 1,5 ml per minute), and the pressure rise is not higher than 20 mmH2O per minute at normal time, while the pressure rise of normal cranial pressure hydrocephalus is higher than this value due to the obstruction of the subarachnoid space at the base of the brain and the decreasing absorption function. Lumbar puncture perfusion is also used to predict the effect of shunt surgery while doing ventricular drainage. The method is to do lateral ventricular puncture placement to determine the initial pressure of cerebral crest fluid outflow, and then perfuse saline into the lumbar puncture with this pressure value, if the resistance of cerebral crest fluid outflow is greater than 12,5 ml per minute per mmHg, then shunt surgery can have better effect.
(4) CT scan of the skull.
The cerebral sulcus becomes shallow, the cerebral gyrus narrows, and the subarachnoid space is not wide, while the effect after shunt is obvious in those with obvious ventricular enlargement and severe periventricular edema.