Patient's question:
My baby has extra-axial cerebrospinal fluid. My baby is 100 days old, can smile, and will coo when someone teases him. However, when doing prone exercises, his head is unstable, and occasionally he can lift it up for a moment but quickly lies down to rub his hands. At the hospital, a CT scan diagnosed him with "extra-axial cerebrospinal fluid" and "motor developmental delay." Is it serious? Findings from the CT scan: Arcuate, water-like density shadows were observed beneath the inner table of the skull on both frontal and temporal regions. The lateral fissure and anterior longitudinal fissure were widened on both sides. No abnormal density foci were seen in the cerebral parenchyma; the third ventricle and both lateral ventricles showed no abnormalities. The midline structures were central. The cranial sutures were not closed. Intelligence test results: Gesell - Operational ability DQ 55, Object ability DQ 9Doctor's answer:
Hello! Your child's motor development is delayed, but it can improve through rehabilitation training. However, it is essential to strengthen the training and not stop it due to the child's crying, as this could do more harm than good and delay the child's recovery. Below is an article written by Dr. Yang Guanying from the First People's Hospital of Foshan, hoping it will be helpful to you:A Brief Discussion on External Hydrocephalus in Infants and Young Children
In our daily work, we often encounter parents of infants and young children with traumatic or hypoxic-ischemic encephalopathy who bring in head CT or MRI scans from other hospitals for consultation. The diagnosis of subdural effusion, brain atrophy, or external hydrocephalus (EH) is based on the observation of symmetrical widening of the subarachnoid space in the frontal or frontoparietal lobes on CT or MRI, causing great concern and fear. Upon further inquiry, we find that the children often have only minor scalp injuries or no symptoms at all, and their growth and development are normal. It is clear that the condition is not caused by subdural effusion, brain atrophy, or hydrocephalus.
Therefore, we provide a detailed explanation to the parents about the causes, prognosis, and other relevant aspects of EH. Most parents then realize it was a false alarm, thank us, and leave with their children happily.
Symmetrical widening of the subarachnoid space (extra-axial space) in the frontal or frontoparietal lobes during infancy and early childhood within a certain range can be a normal physiological phenomenon.
Criteria for Normal Subarachnoid Space Width:
- The width between the cerebral cortex surface and the inner table of the skull in the frontal region is normally 0–4 mm.
- The width of the anterior part of the longitudinal fissure is normally 0–5 mm.
Some studies suggest that the extra-axial space in infants and newborns is relatively wide and follows a pattern of narrowing → widening → narrowing. Newborns have no periventricular spaces or sulci visible, only a narrow longitudinal fissure.
In infants aged 2–12 months, the extra-axial space (subarachnoid space) can be significantly widened, most notably between 2–6 months. By around 2 years of age, most periventricular spaces and sulci disappear, leaving only a relatively narrow longitudinal fissure.
Some authors propose that the widened extra-axial space is due to a temporary imbalance in cerebrospinal fluid (CSF) production and absorption during development, as well as faster skull growth compared to brain tissue after birth. Additionally, as white matter myelination occurs, the brain's water content decreases rapidly from birth to 6 months, leading to a reduction in brain volume. Subsequently, neurocytes proliferate again, increasing brain volume. These factors may contribute to the widening of the extra-axial space, which then gradually narrows—a physiological change.
Thus, diagnosing hydrocephalus based on a widened subarachnoid space in the frontal or frontoparietal lobes within a normal range is incorrect.
When the symmetrical subarachnoid space (extra-axial space) in the frontal or frontoparietal lobes of infants and newborns exceeds the normal physiological range, while other areas are not widened or only slightly widened, it is diagnosed as external hydrocephalus (EH).
Criteria for Abnormally Widened Subarachnoid Space:
- The width between the cerebral cortex surface and the inner table of the skull in the frontal region is greater than 5 mm.
- The width of the anterior part of the longitudinal fissure is greater than 6 mm.
EH is classified as either primary or secondary. Most scholars believe that EH only occurs in infants with open fontanelles, as open sutures are a necessary condition for its development. Temporary reduced CSF absorption, combined with increased CSF secretion by the choroid plexus, can lead to transient communicating hydrocephalus. The hydrocephalus causes intracranial hypertension, but since infants' fontanelles and sutures are not yet closed, the pressure can be relieved through sutural widening and fontanelle bulging, reducing symptoms.
Secondary EH can be caused by various factors, such as hypoxic-ischemic encephalopathy, intracranial hemorrhage, purulent meningitis, hyperbilirubinemia, or prematurity. If the cause cannot be identified, it is classified as idiopathic EH.
Idiopathic external hydrocephalus generally has a good prognosis. Most cases resolve within 2–3 months, and the fluid is fully absorbed by 2–3 years, making it a benign self-limiting condition. No special treatment is needed for asymptomatic children; regular follow-ups should be scheduled, and the condition naturally resolves after fontanelle closure, leaving no long-term sequelae.
Given the potential impact of X-ray radiation on infants, CT scans should not be performed too frequently. It is recommended to repeat them once every 6–12 months.
For secondary EH, treatment depends on the underlying cause and clinical presentation. Mild cases may resolve spontaneously, similar to idiopathic EH. Asymptomatic or occasionally discovered cases may not require treatment. Most children will recover after the cause is addressed, without the need for special interventions to avoid unnecessary suffering for the child and financial burdens for parents.
Severe cases may lead to brain atrophy, and some infants may develop mild neurodevelopmental delays (e.g., psychomotor retardation, transient seizures, behavioral problems, emotional disorders, or even cerebral palsy) between 2 months and 2 years. Therefore, aggressive treatment is necessary for more severe cases of EH.
When the symmetrical subarachnoid space (extra-axial space) in the frontal or frontoparietal lobes is widened in infants and young children, the main differential diagnoses on imaging are subdural effusion and brain atrophy:
1. Subdural Effusion
- Subdural effusion is usually unilateral, becoming bilateral only if asymmetrical.
- The subdural space appears as a "crescent-shaped" hypodense area on the inner side of the skull, with adjacent cerebral surfaces compressed, flattened, and sulci shallow. There is a mass effect.
- Since the arachnoid membrane lies between the dura mater and the inner skull, when the subarachnoid space widens, the arachnoid membrane moves closer to the inner skull. On enhanced scans, point-like vascular shadows (veins) can be seen within the space, adjacent to the inner skull. In contrast, in subdural effusion, the arachnoid membrane is pushed inward, and the vascular shadows are farther from the inner skull.
2. Brain Atrophy
- The widened subarachnoid space is diffuse, not limited to the frontal region, and the interhemispheric fissure is also widened across the entire fissure.
- It is often accompanied by varying degrees of ventricular enlargement.
- CT shows thinning of brain tissue, reduced density, and generalized deepening of sulci, indicating a decrease in brain tissue quantity and quality, with a poor prognosis. Neurological abnormalities and intellectual disabilities are common sequelae.