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The complication of intracranial hemorrhage after craniotomy is not uncommon. The
statistics of 4992 surgical cases surveyed by Kalfas et al. in 1988 showed that postoperative
hemorrhage occurred in 40 cases, with a postoperative hemorrhage rate of 0.8 %. Those
hemorrhages were mainly intracerebral hematoma (60 %), followed by epidural hematoma
(28 %) and subdural hematoma (7.5 %). In the 40 cases, remote hemorrhage from the
surgical area occurred in seven cases. Intracranial tumor surgery was the main reason
for hemorrhage occurrence, accounting for 56 % of cases, in which meningioma was the
main tumor. In the above cases with remote hemorrhage, remote epidural hemorrhage
was the most rare, and its cause is not yet well understood 9]. Fukamachi et al. statistically reviewed 1105 cases of epidural hematoma after craniotomy
in 1986, including 16 cases of postoperative epidural hematoma, in which 10 cases
underwent hematoma evacuation. These 10 cases included four cases involving hematoma
in the operative field, five cases involving hematoma in an adjacent region, and one
case involving hematoma at a distant site 6]. According to the above statistical analysis of cases with a large sample size, the
occurrence of remote epidural hematoma is rare. In this study, a total of 9178 patients
undergoing intracranial tumor resection in the Department of Neurosurgery, First Hospital
of Jilin University, from January 2000 to December 2012 were reviewed, and postoperative
remote epidural hematoma occurred in 14 cases, with an incidence of 0.15 %. These
data only presented the incidence of postoperative epidural hematoma after intracranial
tumor resection in our center. Therefore, calculations of an accurate incidence rate
will require a multi-center study or a larger scale.

The 14 cases of this study were analyzed and showed that these remote epidural hematomas
could be classified based on their location. The first type includes hematomas that
occur at the adjacent site of the ipsilateral surgical area, but not involving the
surgical area; the second type includes hematomas that occur on the contralateral
side of the surgical area; the third type includes remote epidural hematomas involving
the bilateral sides of the surgical area; and the fourth type includes supratentorial
epidural hematomas with infratentorial surgery. In this study, the first type was
the most common (eight cases), followed by the contralateral type (two cases), the
bilateral type (two cases), and the supratentorial epidural hematoma with infratentorial
surgery (two cases). The mechanism of supratentorial remote epidural hematoma after
intracranial tumor resection is still not fully elucidated, though a variety of hypotheses
have been formulated. Currently, it is commonly accepted that intracranial pressure
is reduced after craniotomy due to the substantial loss of cerebrospinal fluid, thereby
increasing the dural venous transmural pressure and inducing blood vessel rupture
after disorder of the vascular regulation occurs, resulting in epidural hematoma 10]–12]. After the bleeding of the torn blood vessels occurs, the dura is stripped off the
inner skull plate to form a hematoma, while the pressure effect produced by the hematoma
increases the transmural venous pressure, aggravating the bleeding and resulting in
hematoma expansion 13], 14]. Some scholars believe that the stretch in the bridging vein due to the brain tissue
collapse after the loss of cerebrospinal fluid and the coagulation abnormalities in
the patients should also be considered important factors 7], 11]. After reviewing the literature, we found that the occurrence of supratentorial remote
epidural hemorrhage after craniotomy was often complicated with either hydrocephalus
or hydrocephalus shunts. These patients all showed substantial loss of cerebrospinal
fluid after surgery, which supported the above hypothesis 7], 13], 15]–17]. In any mechanism, the low intracranial pressure caused by the surgery is the most
important triggering factor. In a neurosurgery, the surgical region is usually located
in the highest point of the brain so that the ipsilateral dura bears the greatest
transmural pressure, with the maximum stretching intensity of the bridging vein. Therefore,
remote epidural hematomas most likely occur on the ipsilateral side of the surgical
region, which may explain the finding in the present study that, of the 14 cases of
hematomas, eight cases occurred on the ipsilateral side and two cases occurred on
bilateral sides, resulting in a total of 10 remote epidural hematomas on the ipsilateral
side.

According to the above assumption of the postoperative remote epidural hematoma after
intracranial tumor resection, the site of supratentorial hemorrhage usually occurs
in the vicinity of the sinus because the dural veins on the brain convexity are small,
often accompanied with arteries and traveling between two layers of dura; thus, the
risk of hemorrhage is relatively low. The anatomical structure of the dura near the
venous sinus is complex. After the veins on the brain surface merge to form the thick
bridging vein, it transits into the sinus at this location. Additionally, arachnoid
granulations in this area easily induce hemorrhage in these structures after the loss
of a large amount of cerebrospinal fluid, leading to increased dural vein transmural
pressure. This increase tends to occur in younger patients because the adhesion between
the dura and the skull in these cases is not very tight 11], 14]. After reviewing the relevant literature, we found that most postoperative supratentorial
remote epidural hemorrhages after intracranial surgery were located near the sinus,
and the patients were relatively young in age, which supports the above speculation
18], 19]. The average age of the patients in this study was 42 years old, which is also in
line with this age characteristic. However, for the first type of epidural hematoma,
which occurred on an adjacent site of the ipsilateral side, it should be noted that,
in addition to the above assumption, the separation of the surrounding adjacent dura
from the inner skull plate during surgery may also induce epidural hematoma because
the stay suture of the dura surrounding the surgery area prevents the spread of the
hematoma toward the surgical area and thus its extension to distant areas, which may
also explain why some of the first types of epidural hematoma did not involve the
sinus, such as the example shown in Fig. 2. In addition, two patients in this study had histories of multiple tumor resection,
including one case of postoperative remote epidural hematoma on bilateral sides (case
11), whose outcome is believed to be related to the previous multiple surgeries, as
the repeated loss of a large amount of cerebrospinal fluid could aggravate a regulation
disorder of the intracranial vascular system, thus causing remote bilateral epidural
hematoma.

The question of whether an epidural hematoma remote from the surgical region was correlated
with the pathological grade of the resected tumor was also analyzed in this study.
Among the 14 examined cases, three cases involved benign tumors, four cases involved
WHO grade I tumors, and seven cases involved WHO grade II tumors. The benign cases
included two cases of pituitary adenoma and one case of tuberculoma (a type of lesion
that is not included in the WHO pathological grading of central nervous system tumors).
Therefore, this study examined seven cases involving benign and WHO grade I tumors
and seven cases involving WHO grade II malignant lesions. Benign and malignant lesions
each accounted for half of the included cases; thus, remote epidural hematoma appears
to be independent of the resected tumor’s pathological grade. Based on a literature
review, numerous similar remote epidural hematomas have been reported after trauma
surgery or hydrocephalus surgery, and these hematomas were clearly related to reduce
intracranial pressure 11], 12], 20].

Among the 14 cases included in this study, there were five meningioma cases. Thus,
the question of whether remote epidural hematoma occurs particularly frequently in
meningioma cases is also examined in this study. The current consensus is that such
remote epidural hematomas are related to craniotomy-induced decreased intracranial
pressure but are not correlated with meningioma 18], 19]. This hypothesis was supported by a 1986 study by Fukamachi et al., who statistically
analyzed 1105 cases involving craniotomy and found that remote epidural hematoma mainly
occurred in patients with hydrocephalus and/or aneurysm 6]. Recently, in 2015, Chung et al. reported three cases of remote epidural hematoma
after brain tumor surgery, none of which involved meningioma; therefore, this type
of remote hemorrhage appears to be independent of brain tumor type 21].

These postoperative remote epidural hematomas after intracranial tumor resection occur
in the epidural region and show no parenchymal damage except for oppression on the
brain tissue; therefore, timely hematoma evacuation can effectively relieve the oppression
of the hematoma on the brain tissue. In this study, 13 out of 14 cases achieved good
prognoses, with satisfactory results in terms of KPS scores. It should be noted that
these epidural hematomas often progresses rapidly. In the present study, seven cases
(50 %) exhibited rapid disease progress, and cerebral hernias had occurred by the
time the hematomas were found, often within 30 min to 5 h after surgery (nine cases).
GCS scores were used to accurately assess the condition of the postoperative remote
epidural hematoma when exacerbation occurred. Although the vast majority of remote
epidural hematomas in the present study achieved satisfactory results after aggressive
treatment, some cases still show poor prognoses. As an example, for the bilateral
epidural hematoma that occurred in case 11, the disease condition was more dangerous
than that of a unilateral hematoma. Due to the hematoma’s rapid progression, the large
bleeding volume, and repeated surgery, even a bilateral hematoma evacuation failed
to save the patient’s life. Therefore, extra attention should be paid to remote epidural
hematomas occurring on bilateral sides, which might result in poor therapeutic effects.