Keywords
subdural hygroma - traumatic brain injury - cerebrospinal fluid - hydrocephalus
Palavras-chave
higroma subdural - traumatismo crânio-encefálico - líquor - hidrocefalia
Introduction
Subdural hygroma is an accumulation of cerebrospinal fluid (CSF)-like fluid in the
subdural space. Macroscopically, it may be either limpid or xanthochromic and slightly
dyed with blood, but on a conventional computed tomography (CT), it appears very similar
to CSF.[1] The following terms have been used as synonyms: subdural effusion, benign subdural
collection, subdural hygroma, traumatic serous meningitis, external hydrocephalus,
and obstructive extraventricular hydrocephalus. This heterogeneity of nomenclature
reflects the controversies regarding the pathophysiologic mechanisms that lead to
its occurrence.[2]
[3]
Subdural hygroma is a common epiphenomenon after a traumatic brain injury (TBI), but
it may also occur after brain surgeries, with different treatment implications. Some
authors believe that a traumatic lesion tears the dura–arachnoid interface, creating
a valve mechanism that forces and traps the CSF into the subdural space.[4] A CSF circulation imbalance should be also accounted for the hygroma origin.[5] In fact, various mechanisms may be responsible for hygromas in different ages, considering
the age predisposition to have an enlarged subdural space.[6]
In children, the pathophysiology of subdural collections is different, and some confusion
exists regarding childhood subarachnoid space enlargement conditions and benign subdural
effusion.[7] This is the reason why subdural collections in children are considered differently
from those of the adults.
Most subdural hygromas are managed conservatively. When necessary, surgical treatment
of hygroma is performed, depending on the cause. A simple external or peritoneal drainage
would generally be advocated in symptomatic cases or in cases with progressive mass
effect on CT scans. A ventricular shunt may be needed when there is a CSF circulation
imbalance.[8]
In this study, we describe the epidemiological features of subdural hygroma in a prospective
case series.
Methods
This is an observational prospective study conducted at a hospital in the city of
Botucatu, SP, Brazil. Patients who had a subdural hygroma diagnosed using the CT scan
were enrolled from January of 2011 to December of 2013. The board of local Ethics
Committee on Research approved the project (CEP 3747/2010), and the patients or family
members signed the informed consent.
All patients from our neurosurgery department who presented a subdural hygroma of
any etiology during their follow-up period were included. Patients with other subdural
collections (such as chronic or acute subdural hematomas and subdural empyemas) were
excluded. Children were also excluded.
Data were collected focusing on sex, age, trauma mechanism or other neurosurgical
intervention, presence of small subdural effusion and subarachnoid hemorrhage and
score on the Glasgow coma scale (GCS) upon admission, time interval from admission
to diagnosis of hygroma, and hygroma treatment.
Results
A total of 17 patients were included; 14 of them were males (82.4%) and 3 females
(17.6%). The mean age was 58.6 ± 20.1 years. Traumatic brain injury (TBI) was the
main mechanism for the occurrence of subdural hygroma (13 patients, 76.5%). Among
these patients, five (38.5%) had been involved in a road traffic accident, four (30.8%)
had fallen from height, and the other four had been beaten. A small subdural effusion
on the initial CT scan was observed in 6 out of 13 patients with TBI (46.2%) and subarachnoid
hemorrhage was observed in 4 (30.8%). Two of the TBI patients (15.5%) had transient
hydrocephalus.
Three patients (17.6%) had the hygroma after a craniotomy, which had been performed
due to other reasons (brain tumor resection, aneurysm clipping, and decompressive
craniectomy). One patient (5.9%) developed the hygroma after a chronic subdural hematoma
drainage, and another patient, after a ventricle–peritoneal shunt.
In our case series, two patients (11.8%) were diagnosed with hygroma through a CT
scan performed to investigate other diseases, and hence considered as incidental hygromas.
[Fig. 1] shows the distribution of cases based on the mechanism of the subdural hygroma.
Fig. 1 Distribution of patients with subdural hygroma based on the developmental mechanism
(n = 17).
The mean time interval between hospital admission and diagnosis of subdural hygroma
was 6.1 ± 5.6 days. When considering patients with TBI only, the mean interval was
still the same. The mean GCS score upon admission was 9.8 (±3.8).
Four patients (23.5%) required a subdural-peritoneal shunt because of deteriorating
clinical condition and enlarged hygroma in subsequent CT scans. All of these patients
were from the TBI group and were victims of road traffic accidents. [Fig. 2] shows a case that needed a shunt.
Fig. 2 Evolution from a small subdural effusion (A) to a subdural hygroma (B); after treating
with a ventricle–peritoneal shunt (C).
Discussion
Subdural hygroma is a common epiphenomenon after head injuries. Despite the benign
course of the majority of cases, some patients may present symptoms from mass effect
and intracranial hypertension.
The first description that explains the occurrence of hygroma was provided by Naffziger,
in 1924. He believed that CSF crosses a breach in the arachnoid membrane.[9] This mechanism explains quite well the hygromas following head injuries and neurosurgeries,
which were the main causes for hygroma in the present series.
However, we also observed incidental hygromas, especially in elderly patients. A possible
explanation for this finding is the understanding that subdural hygromas and hematomas
belong to the same spectrum of disease[10] in which brain atrophy plays a key role.[11]
[12] Previously, subdural hygromas have been observed to change their density on CT or
magnetic resonance imaging (MRI) scans depending on the time, appearing as a subdural
hematoma, and to finally resolve spontaneously.[13]
In patients with head injury, the recognition of early small subdural effusion on
initial CT exam should alert to the risk of evolution to a subdural hygroma.[14] In our series, it took ∼ 6 days from the initial CT to the new CT with a definite
diagnosis of subdural hygroma. Among the four patients who required a surgical intervention
in our series, two had a small subdural effusion on initial CT. Therefore, clinical
condition deteriorations in TBI patients can also be explained by a hygroma with mass
effect.
Another concern in managing subdural hygromas is the concomitance of associated hydrocephalus.
Zanini et al proposed a pathogenesis-based classification that considers the presence
of mass effect and hydrocephalus.[5] In patients with subdural hygroma and hydrocephalus, there is an association of
CSF influx to the subdural space and CSF absorption impairment.[5] Although Zanini et al did not observe hygromas with mass effect and hydrocephalus,
Tsuang et al did; they then proposed that hygromas with mass effect and hydrocephalus
should have drainage and a ventricle shunt.[8]
If identifying hydrocephalus is pivotal in managing subdural hygromas, a variety of
case series has shown progressive extra-axial collections associated with craniectomy,
even with treated hydrocephalus. In fact, subdural hygromas are also common after
a decompressive craniectomy.[15] In patients who underwent craniectomy, were treated for hydrocephalus, and had progressive
extra-axial collection, early cranioplasty is the optimal choice for the collection
resolution.[16]
Conclusions
Based on the analysis of our series, lesions in the dura–arachnoid interface may have
accounted for the majority of cases, as TBI and craniotomy were the main causes of
the subdural hygromas. The findings of incidental hygromas in elderly patients and
their development after performing a ventricular shunt demonstrate that brain atrophy
also plays a significant role in the subdural hygroma formation.
