Table of Contents
Intracranial subdural hygroma
Definition
An intracranial subdural hygroma is a collection of cerebrospinal fluid (CSF) that accumulates within the subdural space of the brain. The subdural space is a potential space between the dura mater (the outermost layer of the meninges) and the arachnoid mater (the middle layer of the meninges). A hygroma typically refers to a fluid-filled sac or collection.
In the context of the brain, a subdural hygroma is different from a subdural hematoma. While a subdural hematoma involves the accumulation of blood in the subdural space, a subdural hygroma consists of clear cerebrospinal fluid without the presence of blood. Hygromas are often associated with trauma, particularly mild head injuries, and can develop gradually over time.
The formation of an intracranial subdural hygroma may be related to disruptions in the normal circulation or absorption of cerebrospinal fluid, leading to an accumulation in the subdural space. This condition can be detected through imaging studies such as computed tomography (CT) scans or magnetic resonance imaging (MRI). The management of subdural hygromas depends on the underlying cause and clinical symptoms, ranging from observation to more active interventions, such as drainage or shunting procedures.
Epidemiology
Intracranial subdural hygromas are relatively rare compared to other intracranial pathologies. The epidemiology of subdural hygromas is not extensively studied, and available data might be limited. However, they are more commonly observed in specific populations and situations:
Traumatic Brain Injury (TBI): Subdural hygromas are often associated with mild to moderate traumatic brain injuries. They can occur in the setting of head trauma, particularly in situations where there is acceleration-deceleration injury or shearing forces that lead to disruption of blood vessels or the arachnoid membrane.
Age and Geriatric Population: There is a tendency for subdural hygromas to be more prevalent in older adults, possibly due to age-related changes in the brain's elasticity and increased susceptibility to subdural space alterations.
Chronic Subdural Hematomas (SDH): Subdural hygromas can sometimes develop as a consequence of chronic subdural hematomas. The resolution of a chronic SDH may leave behind a subdural space that fills with cerebrospinal fluid, forming a hygroma.
Underlying Medical Conditions: Individuals with certain underlying medical conditions or co-morbidities, such as brain atrophy, cerebral atrophy, or connective tissue disorders, may be more prone to developing subdural hygromas.
Post-Surgical Cases: Subdural hygromas can occur as a postoperative complication, particularly in neurosurgical procedures involving the subdural space.
Miscellaneous Causes: While less common, subdural hygromas can also arise spontaneously or due to factors such as cerebrospinal fluid (CSF) overproduction or impaired CSF drainage.
It's essential to note that the true incidence and prevalence of subdural hygromas may be underestimated as they can be asymptomatic and go undetected in many cases. The condition may become more recognized with the increased use of advanced neuroimaging techniques and heightened awareness among healthcare professionals.
Kim et al. suggested that increased cerebrospinal space and cerebrospinal fluid pressure may result in compensatory enlargement of head circumference only in the infant period, and the subdural hygroma thickness decreases with age during the infant and toddler phases 1).
Classification
Etiology
Subdural hygromas most commonly occur when events such as head trauma, infections, or cranial surgeries happen in tandem with brain atrophy, severe dehydration, prolonged spinal drainage, or any other event that causes a decrease in intracranial pressure.
Han et al. reviewed the medical records of 229 patients who underwent microsurgical clipping for unruptured intracranial aneurysms (UIA) from 2016 to 2019. Risk factors for SDG and cSDH formation were analyzed.
Male sex, age ≥ 60 years, higher degree of arachnoid dissection, severe brain atrophy, and a large volume of subdural fluid collection (SFC) before discharge were independent risk factors for SDG formation. The risk factors for hemorrhagic conversion from SDG were continuous use or early resumption of antiplatelet drugs (odds ratio (OR): 15.367, 95% CI: 1.172-201.402) and a larger volume of SFC before discharge (OR: 0.932, 95% CI: 0.886-0.980). In the early resumption group, antiplatelet drug was resumed at a mean duration of 7.48 days postoperatively, and hemorrhagic conversion was detected earlier than that in the late resumption or no-use groups (4.09 vs. 7.18 weeks, P = 0.046). Following the receiver operating characteristic analysis, the SFC cutoff volume for hemorrhagic conversion was determined to be 23.55 mL.
These findings can assist clinicians in identifying patients at a high risk of SDG and cSDH formation. Antiplatelet resumption and its timing should be determined with consideration of the risk of cSDH formation as well as individual medical conditions 2)
Clinical features
Clinical features of intracranial subdural hygroma can vary depending on factors such as the size of the hygroma, the rate of fluid accumulation, and the presence of any underlying pathology. In some cases, subdural hygromas may be asymptomatic and discovered incidentally on imaging. However, when symptoms are present, they can include:
Headache:
Mild to moderate headaches are a common symptom. The nature and location of the headache may vary. Dizziness and Imbalance:
Patients may experience feelings of dizziness or imbalance. This can be related to the increased intracranial pressure caused by the accumulation of cerebrospinal fluid (CSF). Changes in Mental Status:
Mild cognitive impairment or changes in mental alertness may occur, particularly in larger hygromas or when associated with other intracranial conditions. Nausea and Vomiting:
Elevated intracranial pressure can lead to nausea and vomiting, especially if the hygroma causes compression of surrounding brain structures. Visual Disturbances:
In some cases, patients may experience visual disturbances, such as blurred vision or changes in visual acuity. This can be due to compression of optic nerve structures. Weakness or Motor Deficits:
Depending on the location and size of the hygroma, there may be weakness or motor deficits, especially if the hygroma compresses adjacent brain regions. Seizures:
Although less common, some patients may present with seizures if the hygroma affects areas of the brain involved in seizure control.
Diagnosis
The diagnosis of intracranial subdural hygroma involves a combination of clinical assessment and imaging studies. Here are the key steps in the diagnostic process:
1. Clinical Assessment:
Patient History: A thorough history-taking is essential to identify any trauma, surgical interventions, or underlying medical conditions that may contribute to the development of a subdural hygroma. Symptoms: Patients may present with symptoms such as headache, dizziness, changes in consciousness, or neurological deficits. The timeline of symptom onset and progression is crucial. 2. Neurological Examination:
A comprehensive neurological examination is performed to assess cognitive function, motor skills, reflexes, and sensory perception.
3. Imaging Studies:
Computed Tomography (CT) Scan: CT scans are often the initial imaging modality used to visualize the brain structures. A subdural hygroma may appear as a hypoattenuating collection, typically without the hyperdensity associated with blood seen in subdural hematomas.
Magnetic Resonance Imaging (MRI): MRI provides detailed images of brain structures and is particularly useful for distinguishing between different types of fluid collections. A subdural hygroma may present as a hyperintense fluid collection on T2-weighted images.
4. Differential Diagnosis:
The clinician considers and rules out other potential causes of fluid collections, such as chronic subdural hematoma, arachnoid cysts, or postoperative collections. 5. Lumbar Puncture (if necessary):
In some cases, a lumbar puncture may be performed to analyze the cerebrospinal fluid (CSF) composition and pressure, helping to rule out conditions such as idiopathic intracranial hypertension. 6. Multidisciplinary Consultation:
Collaboration with neurosurgeons, neurologists, and radiologists is crucial for accurate diagnosis and planning appropriate management. 7. Follow-up Imaging:
Serial imaging studies may be necessary to monitor the evolution of the hygroma and assess response to treatment if intervention is considered. 8. Consideration of Underlying Etiology:
Identifying and addressing the underlying cause, such as trauma, surgery, or an underlying medical condition, is crucial for a comprehensive approach to management. The combination of clinical evaluation and imaging studies is crucial for a precise diagnosis of intracranial subdural hygroma.
Differential diagnosis
Subdural effusion is a more general term that can encompass various fluids, including blood, while subdural hygroma specifically refers to the accumulation of cerebrospinal fluid. The underlying causes and clinical implications may differ based on the specific type of fluid present.
Classically chronic subdural hematoma contains dark “motor oil” fluid that does not clot. When the subdural fluid is clear (CSF), the collection is termed a subdural hygroma.
The various terms used to describe subdural fluid collection—“external hydrocephalus,” “subdural hygroma,” “subdural effusion,” “benign subdural collection,” and “extraventricular obstructive hydrocephalus”—reflect the confusion surrounding the diagnoses of these diseases. Differentiating external hydrocephalus from simple subdural hygroma may be difficult, but the former appears to be a distinct clinical entity separate from the latter.
The diagnosis of intracranial subdural hygroma involves considering various differential diagnoses, as the clinical presentation and imaging findings may overlap with other intracranial conditions. Here are some conditions that may be considered in the differential diagnosis:
Chronic Subdural Hematoma (SDH):
Differentiating Features: Chronic SDH involves the accumulation of blood in the subdural space, and it may have a similar appearance on imaging. However, the presence of blood in SDH distinguishes it from a hygroma.
Subdural Effusion:
Differentiating Features: Subdural effusion refers to the accumulation of serous fluid in the subdural space. The distinction between subdural effusion and hygroma may be subtle, and clinical context and imaging characteristics are crucial for differentiation.
Arachnoid Cyst:
Differentiating Features: Arachnoid cysts are congenital or acquired fluid-filled sacs within the arachnoid membrane. They are typically located in the arachnoid cisterns, and their communication with the subdural space may mimic a hygroma.
Postoperative Fluid Collections:
Differentiating Features: Following neurosurgical procedures, fluid collections may occur in the subdural space. Distinguishing between postoperative collections and hygromas may require considering the patient's surgical history and timing of symptom onset.
Cerebral Atrophy:
Differentiating Features: Cerebral atrophy can lead to an enlargement of the subarachnoid spaces. Differentiating between cerebral atrophy and hygromas may be challenging, and clinical context and imaging characteristics are essential.
Idiopathic Intracranial Hypertension (IIH):
Differentiating Features: IIH is characterized by elevated intracranial pressure without an apparent cause. It may present with similar symptoms, such as headache and visual disturbances. Imaging studies and lumbar puncture for cerebrospinal fluid pressure measurement help differentiate IIH from hygromas.
Other Fluid Collections:
Differentiating Features: Various other conditions can lead to fluid collections in the intracranial space, such as cystic lesions, ventricular abnormalities, or congenital malformations. Specific imaging characteristics and clinical history aid in distinguishing these entities from subdural hygromas. The definitive diagnosis often relies on imaging studies, such as computed tomography (CT) scans or magnetic resonance imaging (MRI), coupled with a thorough clinical evaluation.
Treatment
Case reports from the General University Hospital Alicante
I14387
The patient is an 83-year-old male with Diabetes Mellitus (DM), Hypertension (HTN), Dyslipidemia (DLP), and a long-standing history of active smoking for more than 65 years. He also has a medical history of Benign Prostatic Hyperplasia (BPH), Hyperuricemia, and Chronic Obstructive Pulmonary Disease (COPD). The patient's medications include a combination of antihypertensive, antidiabetic, lipid-lowering, and other medications to manage comorbidities.
The patient presented to the Neurosurgery department following a traumatic brain injury (TBI) sustained from a fall off a chair. The primary complaints included occipital contusion and a reported loss of hearing post-impact. Additionally, the family reported a chronic history of dizziness, increased weakness in the lower limbs, and instability.
Clinical Examination on Admission:
Glasgow Coma Scale (GCS): 15, without neurological focalities.
Evident occipital hematoma.
Diagnostic Imaging:
A cranial CT scan revealed chronic bilateral subdural hygromas. Extra-axial collections were identified on both convexities, measuring approximately 12 mm (right) and 13 mm (left). Noteworthy findings included a hyperdense lamina in the left frontotemporo-parietal cortex, suggesting recent bleeding foci. Furthermore, a focus of subarachnoid hemorrhage was observed in the basal region of the left temporal lobe. No evidence of fractures was identified. The midline was centralized, and the cisterns at the base were unoccupied. Corticocortical atrophy and findings suggestive of mild small vessel ischemic disease were also noted.