Evaluation of CSF spaces and types of hydrocephalus
Changes in cerebrospinal fluid volume require careful differential diagnosis, as not every expansion of spaces is true hydrocephalus.
- True hydrocephalus: diagnosed exclusively when the internal reservoirs (ventricles) enlarge, compressing and reducing the external spaces.
- Normal-pressure hydrocephalus (NPH): characterized by enlargement of the ventricles alone, while cerebral sulci remain of normal width.
- Brain atrophy: tissue degenerates, and the freed space is proportionally filled with CSF (both subarachnoid spaces and ventricles expand). Using the term hydrocephalus ex vacuo for this condition is no longer recommended.
- Degenerative pathologies: also cause uniform expansion of all CSF-containing cavities.
Diagnostic puncture in normal-pressure hydrocephalus
A classic example of using lumbar puncture as a diagnostic test is the clinical presentation of NPH in elderly patients. The disease manifests with a specific triad:
- Pelvic disorders: urinary urgency and incontinence (often mistaken for urological problems).
- Motor deficit: gait apraxia (wide-based gait, instability, difficulty lifting feet off the floor).
- Cognitive decline: progressive inattention and forgetfulness.
To confirm the diagnosis, a puncture is performed with the evacuation of a large volume of CSF (about 40 ml). If gait markedly improves and incontinence resolves after the procedure, the diagnosis is confirmed. Cognitive impairment, however, does not resolve. MRI in such patients (T2 and FLAIR sequences) reveals the flow void phenomenon—areas of signal void around the cerebral aqueduct and ventricles due to accelerated CSF pulsation. Radical treatment is achieved via surgical shunting.
Impact of CSF accumulation on different age groups
The clinical presentation of intracranial hypertension (ICH) differs radically depending on the degree of skull ossification.
In infants during the first year of life, sutures and fontanelles are open. This compensates for pressure increases: the head enlarges disproportionately fast, fontanelles tense, and veins engorge. The "setting-sun" sign (upward gaze palsy) is characteristic. As long as expansion reserves are not exhausted, the stage is compensated. In decompensation, acute symptoms arise, including projectile vomiting. CT and MRI are mandatory to rule out subdural hematomas or hygromas.
In adults and older children, the skull is a rigid box. Excess CSF immediately causes:
- Bursting headache and morning vomiting on an empty stomach.
- Meningeal signs and photophobia.
- Papilledema, Parinaud's syndrome, and abducens nerve palsy.
- Depression of consciousness.
Technique for identifying meningeal signs
Irritation of the meninges (including by extravasated blood or inflammatory CSF) triggers reflexive tonic muscle responses. The main diagnostic tests are:
- Nuchal rigidity: the physician cannot passively bring the chin of a supine patient to the sternum due to marked resistance.
- Kernig's sign: a leg flexed at a right angle at the hip and knee cannot be fully extended due to spasm of the leg flexors.
- Brudzinski's signs:
- Upper: when checking for neck rigidity, the patient's legs flex involuntarily.
- Middle: pressure on the pubic symphysis causes hip and knee flexion.
- Lower: attempting to straighten one leg (while testing Kernig's sign) causes the other leg to flex.
- Bechterew's sign: light tapping on the zygomatic arch provokes a pain grimace on the side of percussion.
Disorders of CSF circulation in hemorrhage
Acute vascular events directly affect CSF circulation. For example, rupture of a middle cerebral artery aneurysm causes a subarachnoid hemorrhage (SAH). Patients describe the headache as sudden and "thunderclap".
The pathogenesis is related to extravasated blood elements physically blocking CSF outflow and resorption pathways. As a result, non-communicating (arerorptive) hydrocephalus rapidly develops. On CT scans, blood appears bright (hyperdense) and fills the basal cisterns. Due to reflux, some blood may enter the markedly dilated ventricles. Because blood is denser than CSF, it settles in the posterior horns, forming a clear horizontal level on scans between the dark CSF and the bright sediment. An emergency measure in such cases is the placement of an external ventricular drain.
Briefly: answers to topical questions
At what anatomical spinal level is lumbar puncture performed in adults and children?
In adults, lumbar puncture is performed in the intervertebral space between the fourth and fifth lumbar vertebrae (L4–L5). The anatomical landmark for needle insertion is the spinous process of L4, through which Tuffier's line (the horizontal line connecting the iliac crests) passes. The choice of this level is due to the fact that in adults, the spinal cord terminates higher—at the level of the first or second lumbar vertebra. Information on the anatomical level for puncture in children is not provided in the sources.
Which anatomical structures (layers) does the needle successively pass through during lumbar puncture?
During a lumbar puncture, the needle successively passes through six anatomical layers.
- Skin — the outer integument.
- Lumbar fascia — the connective tissue sheath.
- Supraspinous ligament (lig. supraspinale) — the ligament running along the tips of the spinous processes.
- Interspinous ligament (ligg. interspinalia) — the structure between the spinous processes.
- Ligamentum flavum (ligamentum flavum) — the ligament connecting the vertebral arches.
- Dura mater — the outer meningeal layer of the spinal cord.
After passing through the dura mater, the needle enters the subarachnoid space.
What are the absolute and relative contraindications for lumbar puncture?
Contraindications to lumbar puncture are formulated differently across the sources.
Absolute contraindications:
- Progressive brain edema — due to the high risk of displacement syndrome / cerebellar tonsillar herniation through the foramen magnum.
- Increased bleeding tendency — risk of traumatic ("bloody") tap, which distorts the diagnostic picture.
Also indicated as contraindications to lumbar puncture:
- Infectious process at the puncture site.
- Space-occupying brain lesion.
- Elevated intracranial pressure — high risk of brain herniation upon CSF removal.
- Progressive cerebral edema.
- Herniation syndrome.
- Hemorrhagic diathesis or high risk of its development.
A clear division of all the listed conditions into absolute and relative contraindications is not provided in the sources.
What changes in cerebrospinal fluid laboratory parameters (cytosis, protein, glucose) are characteristic of subarachnoid hemorrhage?
Subarachnoid hemorrhage is characterized by specific changes in the cerebrospinal fluid reflecting the presence of blood in the subarachnoid space.
- Cytosis — pronounced erythrocytic cytosis is detected (e.g., 400 cells/µL with a predominance of erythrocytes).
- Protein — an increased protein level is noted (e.g., up to 0.8 g/L), and the Pandy test is strongly positive (+++).
- Glucose — data on changes in glucose levels in this pathology are absent.
Visually, the CSF is bloody, and after centrifugation or sedimentation, an erythrocyte pellet and xanthochromia of the supernatant are determined.
What complications may arise following a lumbar puncture?
The sources explicitly indicate the following potential complications and risks for lumbar puncture:
- Post-lumbar puncture headache — to reduce its risk, the use of thin spinal needles (25G or smaller), preferably with a pencil-point tip, is recommended.
- Brain herniation / brain displacement — the risk increases in the presence of elevated intracranial pressure, a brain mass lesion, progressive cerebral edema, or herniation syndrome.
- Traumatic tap in the presence of a bleeding diathesis — this can distort the diagnostic picture of the CSF.
Other complications specific to lumbar puncture are not explicitly listed in the provided sources.
Brudzinski's signs are easy to remember by the topography of the stimulus from top to bottom: upper — head flexion, middle — pressure on the pubic symphysis, lower — leg manipulation. The response is always the same — leg flexion.
Class and exam questions
Is the diagnosis of "hydrocephalus ex vacuo" still used today?
No, this term is considered obsolete and is not recommended for use. This condition is more correctly referred to as cerebral atrophy with proportional enlargement of the CSF spaces.
Why doesn't memory improve following a puncture in patients with normal pressure hydrocephalus (NPH)?
Evacuation of 40 ml of CSF temporarily reduces pressure on motor tracts, eliminating gait apraxia and urinary incontinence; however, cognitive impairments are generally irreversible and merely stop progressing with the puncture.
How to differentiate blood from CSF in the ventricles on CT?
Fresh blood has high density and appears bright (hyperdense) on CT, whereas CSF appears dark (hypodense). In hemocephaly, blood settles in the posterior horns due to gravity, forming a clear boundary.
What else to study on this topic
- Methodology and technique of classical lumbar puncture
- CNS developmental anomalies associated with hydrocephalus (Chiari malformation, spina bifida)
- Neurosurgical methods: types of cerebrospinal fluid shunting
- Parinaud syndrome and cranial nerve palsies in intracranial hypertension
- Differential diagnosis of macrocephaly: subdural hematoma and hygroma
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