A subdural hygroma (SDG) is a collection of

cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless Extracellular fluid#Transcellular fluid, transcellular body fluid found within the meninges, meningeal tissue that surrounds the vertebrate brain and spinal cord, and in the ventricular system, ven ...

(CSF), without blood, located under the dural membrane of the brain. Most subdural hygromas are believed to be derived from chronic

subdural hematomas A subdural hematoma (SDH) is a type of bleeding in which a collection of blood—usually but not always associated with a traumatic brain injury—gathers between the inner layer of the dura mater and the arachnoid mater of the meninges surroun ...

. They are commonly seen in elderly people after minor trauma, but can also be seen in children following infection or trauma. One of the common causes of subdural hygroma is a sudden decrease in pressure as a result of placing a ventricular shunt. This can lead to leakage of CSF into the

subdural space The subdural space (or subdural cavity) is a potential space that can be opened by the separation of the arachnoid mater from the dura mater as the result of trauma, pathologic process, or the absence of cerebrospinal fluid as seen in a cadaver. ...

especially in cases with moderate to severe

brain atrophy Cerebral atrophy is a common feature of many of the diseases that affect the brain. Atrophy of any tissue means a decrement in the size of the cell, which can be due to progressive loss of cytoplasmic proteins. In brain tissue, atrophy describes ...

. In these cases, symptoms such as mild fever, headache, drowsiness and confusion can be seen, which can be relieved by draining this subdural fluid.

Etiology and Pathophysiology

Subdural hygromas require two conditions in order to occur. First, there must be a separation in the layers of the

Meninges In anatomy, the meninges (; meninx ; ) are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in the subarachnoid spac ...

of the brain. Second, the resulting subdural space that occurs from the separation of layers must remain uncompressed in order for CSF to accumulate in the subdural space, resulting in the hygroma. The

arachnoid mater The arachnoid mater (or simply arachnoid) is one of the three meninges, the protective membranes that cover the brain and spinal cord. It is so named because of its resemblance to a spider web. The arachnoid mater is a derivative of the neural cr ...

is torn and

(CSF) from the

subarachnoid In anatomy, the meninges (; meninx ; ) are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in the subarachnoid sp ...

space accumulates in the subdural space. Hygromas also push the subarachnoid vessels away from the

inner table of the skull The calvaria is the top part of the skull. It is the superior part of the neurocranium and covers the cranial cavity containing the brain. It forms the main component of the skull roof. The calvaria is made up of the superior portions of the f ...

. Subdural hygroma can appear in the first day, but the mean time of appearance is 9 days on

CT scan A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or ...

. Subdural hygroma does not have internal membranes that can easily rupture like

subdural haematoma A subdural hematoma (SDH) is a type of bleeding in which a collection of blood—usually but not always associated with a traumatic brain injury—gathers between the inner layer of the dura mater and the arachnoid mater of the meninges surroun ...

, but hygroma can sometimes occur together with hemorrhage to become hematohygroma. Subdural hygromas most commonly occur when events such as head trauma, infections, or cranial surgeries happen in tandem with

, severe dehydration, prolonged spinal drainage, or any other event that causes a decrease in intracranial pressure. This provides the basis for why subdural hygromas more commonly occur in infants and elderly; infants have compressible brains while elderly patients have a greater amount of space for fluid to accumulate due to brain atrophy from age.

Signs and symptoms

Most subdural hygromas are small and clinically insignificant. A majority of patients with SDG will not experience symptoms. However, some commonly reported but nonspecific symptoms of SDG that have been reported include headache and nausea. Focal neurologic deficits and seizures have also been reported but are nonspecific to SDG. Larger hygromas may cause secondary localized mass effects on the adjacent brain

parenchyma upright=1.6, Lung parenchyma showing damage due to large subpleural bullae. Parenchyma () is the bulk of functional substance in an animal organ such as the brain or lungs, or a structure such as a tumour. In zoology, it is the tissue that ...

, enough to cause a neurologic deficit or other symptoms. Acute subdural hygromas can be a potential

neurosurgical Neurosurgery or neurological surgery, known in common parlance as brain surgery, is the medical specialty that focuses on the surgical treatment or rehabilitation of disorders which affect any portion of the nervous system including the brain, s ...

emergency, requiring decompression. Acute hygromas are typically a result of head trauma—they are a relatively common posttraumatic lesion—but can also develop following neurosurgical procedures, and have also been associated with a variety of conditions, including dehydration in the elderly,

lymphoma Lymphoma is a group of blood and lymph tumors that develop from lymphocytes (a type of white blood cell). The name typically refers to just the cancerous versions rather than all such tumours. Signs and symptoms may include enlarged lymph node ...

and

connective tissue disease Connective tissue diseases (also termed connective tissue disorders, or collagen vascular diseases), are medical conditions that affect connective tissue. Connective tissues protect, support, and provide structure for the body's other tissues a ...

Diagnosis

In CT scan, subdural hygroma will have same density as the normal CSF. Meanwhile, in MRI, subdural hygroma will have same intensity with CSF. If

iodinated contrast Iodinated contrast is a form of water-soluble, intravenous radiocontrast agent containing iodine, which enhances the visibility of vascular structures and organs during radiography, radiographic procedures. Some pathologies, such as cancer, have p ...

is administered during CT scan, the hygroma will produce high density because of the contrast at 120 kVp. However, at 190 kVp, hygroma with contrast will have intermediate density. In the majority of cases, if there has not been any acute trauma or severe neurologic symptoms, a small subdural hygroma on the head CT scan will be an incidental finding. If there is an associated localized

mass effect ''Mass Effect'' is a military science fiction media franchise created by Casey Hudson. The franchise depicts a distant future where humanity and several alien civilizations have colonized the galaxy using technology left behind by Elder race, a ...

that may explain the clinical symptoms, or concern for a potential chronic SDH that could rebleed, then an MRI, with or without neurologic consultation, may be useful. It is not uncommon for chronic subdural hematomas (SDHs) on CT reports for scans of the head to be misinterpreted as subdural hygromas, and vice versa.

Magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to generate pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and ...

(MRI) should be done to differentiate a chronic SDH from a subdural hygroma, when clinically warranted. Elderly patients with marked cerebral atrophy, and secondary widened subarachnoid CSF spaces, can also cause confusion on CT. To distinguish chronic subdural hygromas from simple brain atrophy and CSF space expansion, a

gadolinium Gadolinium is a chemical element; it has Symbol (chemistry), symbol Gd and atomic number 64. It is a silvery-white metal when oxidation is removed. Gadolinium is a malleable and ductile rare-earth element. It reacts with atmospheric oxygen or moi ...

-enhanced MRI can be performed. Visualization of cortical veins traversing the collection favors a widened subarachnoid space as seen in brain atrophy, whereas subdural hygromas will displace the cortex and cortical veins.

Treatment

Most subdural hygromas that are asymptomatic do not require any treatment. Some might opt to perform a simple burr-holes to alleviate intracranial pressure (ICP). Occasionally a temporary drain is placed for 24-48 hours post op. In recurrent cases a

craniotomy A craniotomy is a surgery, surgical operation in which a bone flap is temporarily removed from the Human skull, skull to access the Human brain, brain. Craniotomies are often critical operations, performed on patients who are suffering from brain ...

may be performed to attempt to locate the location of the CSF Leak. In certain cases a shunt can be placed for additional drainage. Great caution is used when choosing to look for the CSF leak due to them generally being difficult to spot.

References

*Taveras, Juan M. et al., eds. ''Radiology: Diagnosis, Imaging, Intervention''. 1994- ; ch. 37: 9-13. *''Brain Inj'' 1998 Jul;12(7):595-603. *McCluney KW, Yeakley JW, Fenstermacher MJ, et al. «Subdural hygroma versus atrophy on MR brain scans: "the cortical vein sign"». AJNR ''Am J Neuroradiol'' 1992;13: 1335–39.

External links

* https://thejns.org/focus/view/journals/neurosurg-focus/26/6/article-pE8.xml {{DEFAULTSORT:Subdural Hygroma Neurological disorders