Intracranial pressure definition and physiology.
1.Intracranial pressure refers to the pressure in the cranial cavity, and the pressure of cerebrospinal fluid is commonly used clinically to indicate the intracranial pressure, which is 70-200 mmH2O in normal adults.
2.The main contents of the cranial cavity are cerebrospinal fluid, blood and brain tissue. Under normal conditions, the volume of the cranial cavity is compatible with the total volume of the contents it contains and keeps the appropriate pressure in the cranial cavity.
3, The total volume of the three intracranial contents in the normal state is basically constant, and the volume of any one or two of the three substances increases, and the other two or one decreases compensatorily to balance the intracranial pressure.
Hypocranial pressure syndrome is a group of rare syndromes with intracranial pressure <60mmH2O, which can be divided into spontaneous hypocranial pressure syndrome and secondary hypocranial pressure syndrome.
Diagnostic points.
The main manifestation of intracranial pressure below 30-60mmH2O – positional headache.
Low cranial pressure headache: headache or headache significantly worsens within 15min of taking upright position, and headache disappears or relieves low cranial pressure syndrome within 30min of lying down position.
I. Secondary hypocranial pressure syndrome can be caused by clear causes.
1, excessive leakage of cerebrospinal fluid due to lumbar puncture, head and neck trauma and surgery, ventriculoperitoneal shunt, etc.
2, dehydration, diabetic ketoacidosis, uremic syndrome, severe systemic infection, meningoencephalitis, hyperventilation and hypotension can reduce the production of cerebrospinal fluid.
Second, the concept of spontaneous hypocranial pressure syndrome.
Spontaneous hypocranial pressure syndrome SIH was first described by German neurosurgeon Schaltenbrand in 1938. The syndrome is rare, without a history of trauma or lumbar puncture, and the duration of SIH varies from a few weeks to a few months, with a predilection for women. It is more frequent in women than in men, with a ratio of 3:1, and the age of onset is mostly 20-40 years.
The main clinical feature is postural headache, which generally has a good prognosis and often resolves spontaneously, but cases of combined subdural hematoma leading to emergency surgery have also been reported, so attention should be paid in the diagnosis and treatment of SIH.
III. Spontaneous hypocranial pressure syndrome – pathogenesis Three possible pathogenic mechanisms of SIH.
1, Excessive underproduction of CSF (impaired secretion).
2, excessive absorption of CSF (absorption disorder).
3, leakage of CSF due to small tears in the cerebral (spinal) membranes.
It has also been suggested that choroid plexus dysfunction will lead to a possible hypocranial pressure and cerebral and meningeal congestion due to CSF underproduction: so far, the only evidence supporting this theory is the increased CSF protein and erythrocyte content in SIH patients.
Spontaneous hypocranial pressure syndrome – clinical manifestations I. Postural headache The headache is severe in sitting or standing position, but it is quickly relieved or disappears when lying down. The headache is variable in location and is distending, pulling, drilling or pulsating pain.
4. Pathogenesis
1. The protective “water cushion” buffering effect of cerebrospinal fluid on the brain and spinal cord is weakened or disappeared, and the brain tissue sinks due to gravity, so that the dura mater, arteries, veins and nerves at the base of the brain are pressed on the uneven skull base, especially the anterior and posterior skull concavities are more obvious, and the pain-sensitive tissues at the base of the skull are stretched.
2. compensatory dilation of meningeal vessels
The pressure difference between the intracranial and spinal cord cavities increases, and the brain tissue is displaced downward. 2. Auditory symptoms: auditory hypersensitivity, hearing loss, tinnitus. 3. Visual symptoms: visual field defects, diplopia, transient dark haze, nystagmus, and nystagmus are seen in 30% of cases. 4. Symptoms are in the posture-related spontaneous hypocranial pressure syndrome
V. Laboratory tests Lumbar puncture.
CSF pressure below 70 mm H2O, mild leukocytosis, increased protein content, red blood cells may be mildly increased Spontaneous hypocranial pressure syndrome – imaging manifestations.
VI. CT
1, Most of the reported SIH patients have normal cranial CT.
A few patients have narrowing of the lateral ventricles, third ventricle, fourth ventricle, basal pool and cortical sulcus, but this is a temporary reversible phenomenon, probably related to cerebral edema, which disappears after the clinical symptoms disappear.
Subdural hematoma is present in about 10% of patients.
The absence of enhancement of the meninges on enhancement scans is related to the low sensitivity of CT.
MR
1. Dural thickening: T2WI shows a slightly high signal dura that is mildly and widely uniformly thickened.
Abnormal enhancement of the meninges: It is characterized by diffuse linear enhancement of the meninges of the cerebral convexity and the cerebellar curtain, and significant enhancement of the ventricular choroid plexus, which is most obvious in the dural sinus.
3. Displacement of brain structures: more than half of the patients may have subungual herniation of the cerebellar tonsils; ventral pressure of the brainstem to the slope, compression and displacement of the cerebral bridge and mesencephalon, narrowing or occlusion of the anterior pontine pool; distortion or downward displacement of the optic cross; downward displacement of the opening of the midbrain aqueduct; disappearance of the suprasellar pool and compression of the pituitary gland. The above phenomena are collectively referred to as “hypophysis”.
4.Subdural fluid and subdural hematoma: About 10% of patients can have subdural fluid. The thickness of the subdural fluid is usually < 1 cm, and there is no occupational effect.
VIII. Imaging manifestations.
MR scan shows: dural thickening and a small amount of subdural fluid bilaterally.
MR enhancement shows: diffuse linear enhancement of the meninges. （Mechanism of occurrence: Monro-Kellie hypothesis: the sum of brain tissue volume, cerebrospinal fluid volume and intracranial blood volume is constant. The volume of cerebrospinal fluid decreases at low cranial pressure, while the volume of brain tissue remains relatively constant. Therefore, the increase in intracranial blood volume is dominated by compensatory expansion of the venous system, which can only be seen in the dura mater and venous sinuses.
MR manifestations.
1, the substantia nigra is deformed by compression, and the pool becomes smaller.
2. Subdural fluid accumulation, shortening of the long diameter and widening of the transverse diameter of the midbrain.
3. The abdomen of the cerebral bridge is flattened by slope compression, the angle between the large cerebral vein and the straight sinus is 33°, the suprasellar pool disappears, and the pituitary gland is compressed and flattened.
Spontaneous hypocranial pressure syndrome – differential diagnosis 1. Differentiation of meningeal reinforcement infection or inflammation metastatic meningeal carcinoma 2. Differentiation of Chiari malformation high cranial pressure spontaneous hypocranial pressure syndrome – treatment 1. position: head low and feet high position to antagonize the effect of gravity 2. drink water, static drip 0. 45%~0. 9% saline 1500-2500ml/d3. 2500ml/d3, anti-choroid plexus vasospasm: preferred prostaglandin E1 and Nimotone4, hormone: can have negative feedback regulation of the nervous system, immune system5, intrathecal injection of saline and dexamethasone and other drugs6, cerebral vasodilator: commonly used CO2 inhalation, usually mixed with 5% CO2 and 95% O2, 5-10 ml per hour inhalation, for post-traumatic, post-operative low cranial pressure It has good effect on post-traumatic and post-operative low cranial pressure, with vasodilatation, reducing vascular resistance and increasing CSF secretion.
7.Epidural blood patch therapy: that is, injecting autologous venous blood into the epidural space, the amount of blood injected is about 12-20 ml. It is very effective for SIH.
8.Epidural space injection of normal saline When encountering young women in the clinic, postural headache can be relieved by itself, please do not ignore spontaneous hypocranial pressure syndrome.