Cerebral Hygroma: Causes, Symptoms, Risks, and Treatment

What is Cerebral Hygroma?

A cerebral hygroma, also called a subdural hygroma, is an abnormal collection of cerebrospinal fluid (CSF) within the skull, located at the level of the meninges in the subdural space: the region between the dura mater (outermost meningeal layer) and the arachnoid membrane (middle layer).

The most common underlying condition leading to cerebral hygroma is the chronic evolution of a subdural hematoma. Essentially, hygroma represents a chronic complication of blood accumulation between the meninges.

Recent epidemiological data estimate that cerebral hygroma occurs in approximately 5–20% of closed head trauma cases, that is, head injuries that do not involve severe lacerations or skull fractures.

Other, non-traumatic causes of cerebral hygroma include:

• Collapse of the CSF-containing ventricular cavities
• Complications of neurosurgical procedures
• Marked cerebral atrophy
• Therapeutic hyperventilation
• Severe dehydration or excessive use of diuretics

The clinical presentation is predominantly neurological and may include:

• Progressive headache unresponsive to common analgesics
• Nausea and vomiting
• Lethargy and confusional state
• Memory disturbances and speech difficulties
• Shortness of breath
• Syncope, loss of balance, and difficulty walking
• Raised intracranial pressure

Diagnosis relies on clinical history and neurological examination, confirmed by contrast-enhanced CT scan, which also allows differentiation from other cerebrovascular conditions with a similar clinical picture.

Treatment options include:

• Watchful waiting is appropriate only for small, asymptomatic hygromas, which frequently undergo spontaneous reabsorption.
• Surgical drainage: indicated for larger, symptomatic hygromas with significant neurological compromise.

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Anatomy Overview

The meninges are three thin membranes that envelop and protect the structures of the central nervous system (CNS), covering both the brain and the spinal cord.

Their functions extend beyond mechanical protection: the meninges also provide metabolic support to the CNS and regulate the passage of toxic substances and drugs through a structure known as the meningeal barrier, a functional extension of the blood-brain barrier concept.

The three meningeal layers, from outermost to innermost, are:

Between the arachnoid and pia mater lies the subarachnoid space, a virtual cavity through which cerebrospinal fluid (CSF) circulates. CSF performs several critical functions:

• Mechanical protection: cushions the brain and spinal cord against physical trauma.
• Metabolic regulation: facilitates the exchange of nutrients and metabolic waste products between the brain and the bloodstream.
• Intracranial pressure regulation: maintains stable pressure within the cranial vault.

The subdural space, located between the dura mater and the arachnoid, is not normally present as a real anatomical space. It only becomes clinically relevant when pathological processes (such as bleeding or CSF accumulation) create a separation between these two layers.

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Causes

A cerebral hygroma is a collection of CSF that may sometimes appear xanthochromic (yellowish), particularly when it develops as a consequence of leptomeningeal hemorrhage. In such cases, the hemoglobin pigment from red blood cells is progressively converted into bilirubin, giving the fluid its characteristic yellow tint. Hemoglobin levels in associated blood work may also reflect this process.

Pathogenesis

The most widely accepted pathophysiological model proposes the following sequence of events:

1. Arachnoid membrane tear: An initial laceration of the arachnoid mater allows a modest leakage of blood and CSF into the subdural space.
2. One-way valve mechanism: A critical second step involves establishing a unidirectional flow. This flow continuously allows CSF to enter the subdural space but prevents it from flowing back out.
3. Progressive accumulation: Small quantities of CSF accumulate over time when drainage is inadequate. This gradual buildup eventually forms a clinically evident hygroma.

In the majority of cases, hygroma develops as a complication of a subdural hematoma, typically chronic rather than acute. The hematoma becomes surrounded by a newly formed pseudocapsule, within which:

• An increasing oncotic pressure develops.
• This pressure draws CSF into the cavity.
• The pseudocapsule acts as a semipermeable membrane, trapping fluid inside.
• Over time, progressive CSF accumulation dilates the capsule. This process forms a true cerebral hygroma, which is a collection of CSF mixed with small amounts of blood.

Risk Factors

Cerebral hygroma most commonly develops following:

• Subdural hematoma (especially chronic), which itself arises from moderate-to-severe head trauma due to:

  • Road traffic accidents
  • Falls from height (accidental or intentional)
  • Physical assault or combat
  • Contact sports with repeated head impacts (boxing, martial arts)
  • Sports with risk of head collisions (football, rugby)

• Collapse of CSF-containing ventricular cavities

• Complications of neurosurgical procedures

• Marked cerebral atrophy (particularly in elderly patients)

• Therapeutic hyperventilation

• Dehydration or hypernatremia (elevated sodium levels in blood)

• Excessive use of diuretics

• Rarely: chronic cough or vigorous Valsalva maneuvers in elderly patients

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Symptoms and Clinical Course

The clinical evolution of a cerebral hygroma is highly variable.

In many cases, the hygroma remains small and asymptomatic. It does not produce notable neurological deficits and may undergo spontaneous reabsorption. Even small hygromas, however, can sometimes cause irritation of adjacent brain tissue, producing mild symptoms.

When the fluid collection grows significantly over time, it can produce a clinically significant mass effect. This compression may affect surrounding brain structures. The resulting neurological picture depends on the location and size of the hygroma.

Common Symptoms

• Progressive headache: gradual onset, worsening over time, and resistant to standard analgesics.
• Nausea and vomiting, which may include projectile vomiting of central origin in severe cases with raised intracranial pressure.
• Fatigue and general malaise.
• Global cognitive deterioration.
• Lethargy: difficulty maintaining wakefulness or excessive drowsiness.
• Confusional state with disorientation in time and space.
• Memory and language disturbances (including aphasia).
• Movement disorders and impaired locomotion.
• Dyspnea or severe respiratory disturbances, particularly when brainstem respiratory centers are compromised.
• Syncope, loss of balance, and ataxia may occur if the cerebellum is involved.
• Irreversible coma and death: these are the outcomes in the most severe cases, when intracranial hypertension leads to cerebral herniation.

Important: Symptoms typically emerge days to weeks after a head injury and may be insidious in onset, particularly in elderly patients. Any progressive worsening of headache, cognitive function, or level of consciousness after head trauma warrants immediate medical evaluation.

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Complications

Cerebral hygroma carries a variable but generally favorable prognosis, as spontaneous remission with complete reabsorption is common, even without active treatment.

Prognostic factors include:

• Patient age (elderly patients tend to have worse outcomes)
• History of prior subdural hematoma
• Traumatic vs. non-traumatic origin and severity of the causative event
• Baseline clinical conditions and comorbidities
• Speed of diagnosis and treatment

Mortality can reach up to 28% in the most severe cases, and is primarily correlated with the severity of the precipitating head trauma, associated brain injuries, and the size of the hygroma.

Intracranial Hypertension

The most serious complication of cerebral hygroma, though fortunately rare, is raised intracranial pressure (ICP), which represents a true neurological emergency. This condition demands immediate surgical decompression.

As the hygroma enlarges, it progressively compresses brain structures within the rigid confines of the skull. If ICP exceeds critical thresholds, cerebral herniation may occur. This is a catastrophic event that is almost invariably fatal when it involves vital brainstem centers.

Signs and symptoms of raised ICP superimposed on those of hygroma include:

• Severe, sudden-onset headache
• Projectile vomiting without preceding nausea (central-type vomiting)
• Papilledema is optic disc swelling that can be seen during a fundoscopic examination
• Focal neurological deficits, such as facial palsy or brachiocrural paralysis (which affects the upper and lower limbs on one side), may occur

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Diagnosis

Clinical Presentation

Most patients with cerebral hygroma present to the emergency department days after sustaining head trauma, often brought in by a caregiver or family member who reports progressive changes in mental status, worsening headache, nausea, and vomiting. Only rarely do patients present in a comatose state at initial evaluation.

Medical History

A thorough medical history is the essential first step, aiming to reconstruct the full clinical picture:

• History of closed head trauma in the days preceding symptom onset.
• Pre-existing conditions and risk factors for chronic subdural hematoma (e.g., arterial hypertension, coagulation disorders).
• Prior neurosurgical procedures.
• Current medications, particularly anticoagulants or antiplatelet agents that significantly increase bleeding risk, should be carefully reviewed.

Physical and Neurological Examination

A complete neurological examination allows the physician to objectively document:

• Level of consciousness and orientation
• Cognitive function
• Motor and sensory deficits
• Cerebellar signs (balance, coordination, gait)
• Signs of raised intracranial pressure (papilledema, cranial nerve palsies)

Diagnostic Investigations

The following investigations are typically performed:

Contrast-enhanced CT of the brain, performed urgently, is the cornerstone of diagnosis. It typically demonstrates:

• A crescent-shaped hypodense (dark) collection in the subdural space, which is characteristic of a hygroma.
• Evidence of the hygroma as an evolutionary complication of a prior subdural hematoma.
• In rare cases, a first-time finding of hygroma without a prior history of hematoma or trauma.

Differential Diagnosis

Cerebral hygroma must be carefully distinguished from other conditions that can produce a similar clinical and radiological picture:

• Acute or chronic subdural hematoma
• Ischemic stroke
• Intracerebral hemorrhage
• Subarachnoid hemorrhage
• Brain abscess
• Primary brain tumor or secondary brain metastases

The contrast-enhanced CT scan plays a pivotal role in this differential diagnosis, as the imaging characteristics of each condition differ significantly.

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Treatment

Initial Stabilization

The initial management of a symptomatic cerebral hygroma involves a multimodal approach aimed at:

• Stabilizing vital parameters
• Optimizing hydration status and electrolyte balance
• Treating any underlying comorbid conditions

Conservative Management

For small, asymptomatic or mildly symptomatic hygromas, surgical intervention is not required. Spontaneous reabsorption within a few weeks is observed in the majority of cases. However, these patients require:

• Hospital admission for close clinical and instrumental monitoring
• Serial CT scans (e.g., every 30 days) to track radiological evolution
• Neurosurgical follow-up after discharge

The majority of cerebral hygromas resolve spontaneously within 3 months of diagnosis.

Pharmacological Support

The following medications may be used as supportive therapy:

• Antihypertensives help reduce arterial blood pressure and lower vascular stress.
• Analgesics: used for headache and pain control.
• Mannitol, an osmotic diuretic, is used to reduce intracranial pressure and prevent cerebral herniation.
• Blood transfusions and blood products, particularly in cases of acute anemia caused by associated bleeding.

Surgical Treatment

Surgical intervention is reserved for severe cases with:

• Large hygroma volume
• Significant neurological deficits
• Signs or risk of raised intracranial pressure
• Failure of conservative management

The procedure involves surgical drainage of the CSF collection, achieved through one or more burr holes in the skull, with placement of a drain to decompress the adjacent brain structures. The goal is rapid decompression to prevent further neurological damage.

Post-operative recovery requires careful monitoring and follow-up imaging to ensure adequate resolution and detect any recurrence.

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Key Takeaways

• A cerebral hygroma is a CSF collection in the subdural space, most commonly a complication of a chronic subdural hematoma following head trauma.
• It affects approximately 5–20% of closed head trauma patients.
• Symptoms are primarily neurological and range from progressive headache and confusion to coma in the most severe cases.
• Contrast-enhanced CT scan is the gold standard for diagnosis and differential diagnosis.
• Many hygromas resolve spontaneously within 3 months; larger, symptomatic cases require surgical drainage.
• Raised intracranial pressure is the most feared complication and constitutes a neurological emergency.
• Any worsening neurological symptom following head injury should prompt immediate medical evaluation.

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Sources and Bibliography

• Mutani R, Lopiano L, Durelli L, Mauro A, Chiò A. Il Bergamini di Neurologia. Turin: Libreria Cortina Torino.
• Yamashima T, Friede RL. Post-traumatic subdural hygroma. Acta Neuropathol. 1984;64(2):160–166. https://doi.org/10.1007/BF00695979
• Lee KS. The pathogenesis and clinical significance of traumatic subdural hygroma. Brain Inj. 1998;12(7):595–603. https://doi.org/10.1080/026990598122359
• Park SH, Keum DI, Hwang JH, et al. Traumatic Subdural Hygroma: Proposed Pathogenesis and Management. J Korean Neurosurg Soc. 2008;44(6):408–412. https://doi.org/10.3340/jkns.2008.44.6.408
• Zanini MA, Resende LA, Freitas CC, Yamashita S. Traumatic subdural hygromas: proposed pathogenesis based upon CT characteristics. Arq Neuropsiquiatr. 2008;66(3A):525–528. https://doi.org/10.1590/S0004-282X2008000400013
• National Institute of Neurological Disorders and Stroke (NINDS). Traumatic Brain Injury Information Page. Available from: https://www.ninds.nih.gov/health-information/disorders/traumatic-brain-injury
• Servadei F, Nasi MT, Giuliani G, et al. CT Findings and Clinical Evolution of Acute Traumatic Subdural Haematomas and Subdural Hygromas. Acta Neurochir. 1998;140:107–112. https://doi.org/10.1007/s007010050074