CASE REPORT

Subdural Hemorrhage in a Military Aviator
Gordon G. Cable

BACKGROUND:

The occurrence of any intracranial bleeding is highly significant from an aeromedical risk perspective and potentially
career-ending for a military aviator. Where it arises from head trauma, there is always concern regarding ongoing risk of
post-traumatic epilepsy.

CASE REPORT:

A 26-yr-old male military aviator with persistent headache was found to have small right frontal and parietal subacute
subdural hematomas, most likely precipitated by minor head trauma and possibly exacerbated by other concurrent
physiological stressors. The hematomas resolved with conservative management and the aviator made a full recovery.

DISCUSSION:

The association between traumatic subdural hematomas and the occurrence of post-traumatic epilepsy is well documented, and this, together with the possibility of recurrent bleeding, must be considered the significant aeromedical
risks. However, this case presents an unusual situation of small subdural hematomas in isolation with no other features
suggestive of significant traumatic brain injury. Relevant medical literature was found to be substantially lacking, and no
other similar case reports of aviators could be found. An aeromedical decision-making process is discussed in relation to
returning the aviator to flying duties in a restricted capacity.

KEYWORDS:

head injury, post-traumatic epilepsy, aeromedical decision-making, intracranial hematoma.
Cable GG. Subdural hemorrhage in a military aviator. Aerosp Med Hum Perform. 2016; 87(6):575–579.

A

subdural hematoma (SDH) is a collection of blood riding rollercoasters.4,22 In some cases they are considered
between the dura and the arachnoid
layers around
hypothesized causes such as increased
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brain and is the most common type
of traumatic
intra- Medical
intravenous
pressure (forced exhalation against a closed glottis,
Delivered
Ingenta
cranial mass lesion.14 Acute subdural hematomas (ASDH)
are by lifting
heavy weights) and intracranial hypotension (as seen in
14
those less than 72 h old. They are seen commonly in cases of
acute dehydration).20 Natural and iatrogenic volume deplesevere traumatic brain injury (TBI) where there have been tion has been found to be prevalent in elderly subjects prehigh-energy acceleration forces.10 A subdural hematoma that senting spontaneous CSDH;24 however, no association has
is not associated with an underlying brain injury is sometimes
been found with heat-related hypohydration and changes in
termed a simple or pure subdural hematoma. Subacute sub- brain volume which might lead to intracranial hypotension.21
dural hematomas (SSDH) present from 3 to 20 d after acute In younger patients, alcoholism is a more likely association.14
injury,1,18 and should also be suspected with a history of head
SDH associated with TBI carries with it a risk of posttrauma. These are a rarer entity and much less is known about
traumatic epilepsy (PTE). PTE is a recurrent seizure disorder due
them, but they seem to be associated with lower rates of mortal- to brain injury following trauma, and in 90% of cases this presity and morbidity.10 Chronic subdural hematomas (CSDH)
ents within 2 yr of the initial injury.2 Unfortunately, EEG is not
tend to be a disease of the very young and the very old, but useful for predicting the likelihood of PTE developing in any
are relatively rare in young adults.12 CSDH develop over the given patient.11 The seminal paper by Annegers et al.3 in 1998
course of weeks.14 In younger patients they are likely to be a
the RAAF Institute of Aviation Medicine, RAAF Base Edinburgh, South Australia,
much smaller size due to normal brain volume and thinner From
Australia.
subdural space, with head trauma and a defect of hemostasis This manuscript was received for review in February 2016. It was accepted for publication
the most common causes in this group.15 Both SSDH and in March 2016.
Address correspondence to: Gordon G. Cable, P.G.Dip.Av.Med., FACAsM, Royal
CSDH have been linked to seemingly trivial or noncontact
Australian Air Force Institute of Aviation Medicine, RAAF Base Edinburgh, South
forms of head trauma where the mechanism underlying the
Australia 5070, Australia; gordon.cable1@defence.gov.au.
subdural hemorrhage may be unclear. Examples include nonReprint & Copyright © by the Aerospace Medical Association, Alexandria, VA.
contact martial arts and vigorous dance,8 bungee rides,6 and
DOI: 10.3357/AMHP.4570.2016
Aerospace Medicine and Human Performance Vol. 87, No. 6 June 2016   575

SUBDURAL HEMORRHAGE IN AN AVIATOR—Cable

defined severe traumatic brain injury as being characterized by nonexistent or unhelpful, and no other similar case reports of
brain contusion, intracranial hematoma, or loss of consciousness
aviators could be found. A first-principles discussion of the
(LOC) or post-traumatic amnesia (PTA) more than 24 h; moderaeromedical decision-making process and analysis, as far as
ate brain injury was characterized by LOC or PTA of 30 min to possible, of the aeromedical risks based on available literature
24 h or skull fracture; and mild traumatic brain injury was charis presented.
acterized by absence of fracture and LOC or PTA less than 30 min.
The difference in PTE risk between the mild and severe categoCASE REPORT
ries of TBI is substantial. In the first 12 mo after injury, Annegers
reports a standardized incidence ratio for PTE of 3.1 (1.0–7.2)
The patient was a 26-yr-old Air Force Airborne Electronics
for mild and 95.0 (58.4–151.2) for severe traumatic brain injuAnalyst and crewmember of the P3-C Orion maritime patrol
ries. For the severe group an increased risk was found to persist beyond 10 yr post-injury. The univariate ratio of PTE arising aircraft. This is a large multicrew, multi-engine turboprop aircraft with low levels of 6Gz exposure. He had been previously
from SDH only was calculated to be 9.8 (3.6–27.1), with brain
fit
and well, on no prescribed or self-medication, in particular
contusion alone and SDH alone being the strongest risk factors.
anticoagulants.
He had no family history of epilepsy, intracraA more recent retrospective population-based study by Yeh et al.
nial
aneurysm,
or
bleeding.
found that the risk of PTE after TBI was significantly higher than
In
mid-June
2015,
the patient embarked on a European holia control population of non-TBI patients, even in those with mild
day,
including
a
7-d
cruise on a small passenger vessel. The
head injury, and persisted in both mild and severe TBI groups for
weather
during
the
trip
was considered unusually hot for the
25
4 yr. The adjusted hazard ratio calculated for subdural hemortime
of
year,
above
30°C.
The patient was physically very active
rhage was 4.1 (CI 2.2–7.4) compared to brain contusion.
during
the
holiday,
but
endeavored
to maintain fluid intake in the
Studies that categorize subdural hematomas by requirement
warm
conditions.
His
consumption
of alcohol was moderate and
for surgical intervention have found that those requiring neuroconsistent
with
that
of
young
man
on vacation with friends. A
surgical evacuation carry the greatest risk of late seizure (cumulathorough
review
of
the
history
revealed
no significant head
tive 27.8–44% by 2 yr) compared to no surgery (15.3–19% by
trauma
or
fall;
however,
the
patient
recalled
that
at the beginning
5,19
2 yr), but it is clear that that the nonoperated groups still show
of
the
sailing
cruise
on
27
June,
he
was
involved
in a drinking
a significant cumulative incidence. Studies assessing the risk of
game
in
a
pub
that
involved
wearing
an
old
military-style
metal
developing PTE commonly cite the presence of blood in brain
helmet
while
being
struck
with
considerable
force
on
the
top
of
tissue as the underpinning pathophysiology. For example, in the
the
head
by
the
bartender
with
the
full
shot
glass.
case of cerebral contusion, extravasated blood is hemolyzed,
The cruise progressed uneventfully, except for bumping his
resulting in the deposition of hemoglobin in the neuropil. Liberhead
against an upper bunk. He considered it to be a mild
ated iron from hemoglobin and transferrin is sequestered as
bump,
with no bruising or swelling or headache, and thought
hemosiderin, which has been found to be a prominent histopathnothing
more of it. He could recall no other episodes of either
23
ological feature of PTE. Iron in the tissues is toxic due to the
contact
or
noncontact head trauma, such as vigorous shaking.
formation of oxygen free radicals andIP:
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peroxidation. Pres5.188.216.223
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ence or absence of hemosiderin on brain MRI
may, therefore,
be
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used to guide prognosis and assessment of risk.
Recurrence of bleeding in the future must also be considered. The reported incidence in the literature of 9–33% relates
mostly to surgically treated SDH, ignoring the fact that many
SDH patients are treated conservatively. Schmidt et al. conducted a retrospective cohort study of 10,158 patients with
SDH and found that the vast majority of recurrences occurred
within the first 12 mo, after which the risk was very modest.17
The 1-yr cumulative risks were 17.7% and 10.4% for surgically
and conservatively treated patients, respectively. The overall
risk of recurrence increased from 14% at 1 yr to only 15% at
5 yr. Predictors for recurrence included male gender, older age,
alcohol addiction, surgical treatment, trauma, and diabetes.
The occurrence of any intracranial bleeding is highly significant from an aeromedical risk perspective and potentially careerending for a military aviator. Where it arises from head trauma,
there is always concern regarding the ongoing risk of posttraumatic epilepsy. This paper reports an unusual case of multiple small subdural hemorrhages arising from seemingly minor
head trauma in a young and otherwise fit aviator. The medical
literature directly relevant to this case was found to be either
Fig. 1. MRI showing right frontal subdural hematomas.
576  Aerospace Medicine and Human Performance Vol. 87, No. 6 June 2016

SUBDURAL HEMORRHAGE IN AN AVIATOR—Cable

significant enough to result in a hemorrhage other than bumping his head on the bunk bed. By 4 August the headache had
resolved and MRI/MRA showed no vascular abnormalities or
other underlying lesion, with almost complete resolution of the
subdural blood. The patient was assessed by a neurologist on
18 August, who found no focal neurological signs and felt the
mechanism of injury could be related to a combination of dehydration, alcohol intake, and minor head trauma tearing a small
intracerebral vein. On the basis of a normal EEG, he felt
the risk of seizure activity was negligible, as was the risk of a
recurrent subdural. The neurosurgeon expressed a similar
opinion. Medical investigations excluded coagulopathic disorders and alcohol-related issues. INR, APTT, and platelets were
normal. LFTs and CDT were normal with an AUDIT score of 5
(low risk). The aviator’s case was presented to the RAAF Institute of Aviation Medicine for a waiver at 6 mo following the
initial injury.
DISCUSSION
There are two problems in determining the aeromedical risk
in this case with any precision. Firstly, there is a definitional
problem in categorizing the injury as mild, moderate, or
In the days following disembarkation, he continued to consevere. It is an unusual presentation of a small SDH in isolasume a moderate amount of alcohol daily and, while traveling
tion with no other features typical of closed head injury of
by train for 7 h in hot conditions, felt he became quite dehysufficient severity to cause subdural bleeding, such as LOC,
drated with limited access to water.
During the day of 6 July, 9 d after the drinking game, he PTA, skull fracture, or, most importantly, intracerebral connoticed the onset of a mild dull right parietal headache, which tusion. Nonetheless, the presence of intracranial hematoma
became persistent although never severe, rated generally at places him into the severe category according to Annegers’ oft
quoted reference, noting that SDH is generally considered to
2 out of 10 on a visual analog pain scale. It was not associated
be a significant independent risk factor for late seizures folwith photophobia, phonophobia, nausea, or vomiting, although
it was exacerbated by bending down and head-shaking. At the lowing head injury.3,7 Consistent with that, the U.S. Air Force
classify
degree of head injury as severe based on
conclusion of the vacation he returned
to Australia on On:
9 July
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the presence
of SDH and would disqualify for between 2 and
and finally sought medical advice about the
persistentAerospace
headache Medical
Delivered
yr depending on role. Airborne Mission Systems crew are
on 12 July. A CT head scan ordered on 14 July was
initially by 5Ingenta
eligible for early waiver at 2 yr post severe TBI.13 The U.S.
reported as normal; however, retrospective review much later
by a neurologist reported the presence of a “small acute subdu- Navy would permanently disqualify any aviator with any hisral hematoma.” The headache was still present a week later so a tory of intracranial bleeding.16
Secondly, available literature pertinent to this patient was
further MRI brain scan was arranged on 21 July which revealed
found to be imperfect or nonexistent. The majority of the literahyperintense foci overlying the right frontal and parietal lobes
ture relevant to ASDH and SSDH involves moderate to severe
to a maximal radial depth of 3.5 mm, consistent with small subhead trauma and, in the majority of cases, the SDH requires
acute subdural hemorrhages, as shown in Fig. 1 and Fig. 2.
On 23 July, 17 d after symptom onset, he was reviewed by surgical evacuation, which is understood to increase the risk of
PTE substantially.5 The energy of impact is enough to cause
a neurosurgeon, who found him to be neurologically intact
cerebral contusion in 83% of patients with ASDH, axonal injury
despite the presence of the SDH. Conservative management
was advised. He felt the bleed had occurred as a result of dehy- in many, and, therefore, damage to underlying brain parendration and/or minor trauma, although at that time the patient chyma.10 So the risk of PTE estimated in many studies is not
did not report the drinking game and did not report any trauma really relevant to this case, where the energy of impact was relatively low and no surgical interTable I. Risk of PTE Less Than 12 mo and 1–4 yr Post-Injury (Based on Annegers et al.3).
vention was required.
,12 MO
1-4 YR
Applying the strict definitions of TBI to this case, the
SIR* (CI)
SEIZURE RISK %
SIR (CI)
SEIZURE RISK %
presence of SDH categorizes the
Mild TBI
3.1 (1.0–7.2)
0.19 (0.06–0.44)
2.1 (1.1–3.8)
0.55 (0.07–0.23)
Severe TBI
95.0 (58.4–151.2)
5.8 (3.6–9.2)
16.7 (8.4–32.0)
1.02 (0.51–2.01)
injury as “severe” and aeromedical risk can then be calculated
* Standardized incidence ratio.
Fig. 2. MRI showing right parietal subdural hematoma.

Aerospace Medicine and Human Performance Vol. 87, No. 6 June 2016   577

SUBDURAL HEMORRHAGE IN AN AVIATOR—Cable

drop to within aeromedically
acceptable thresholds, as does
the risk of recurrent bleeding.
HR† (CI)
SEIZURE RISK %
HR (CI)
SEIZURE RISK %
Even within the initial 12-mo
Mild TBI
9.01(5.99–13.5)
0.55 (0.36–0.82)
5.20 (3.02–8.94)
0.32 (0.12–0.54)
window, given his normal role
Severe TBI
23.9 (18.9–30.2)
1.46 (1.15–1.84)
7.08 (4.73–10.6)
0.43 (0.29–0.65)
†
in a multicrew aircraft with minHazard ratio.
imal exposure to acceleration
from the available population data. However, mitigating factors
forces and his isolated SDH with no other features consistent
include that the acceleration force was relatively small and with significant TBI, his absolute risk while flying was still
insufficient to cause cerebral contusion, there were no hemosidconsidered to be low. Therefore, it was recommended that this
erin deposits reported in the brain substance, and the SDH
aviator be restricted to his normal multicrew operations and
resolved fully without surgical treatment. Using Annegers’ data
also restricted geographically to flights of short duration within
and using a population risk of single unprovoked seizure of 61 Australia until 12 mo post-injury to mitigate the risk of recurper 100,000 person-years (0.061% per year),9 Table I examines rence and of PTE, and to expedite his access to acute medical
the risk of PTE for both mild and severe TBI at less than 12 mo care in the unlikely event it is required. Thereafter consideration
post-injury and from 1–4 yr post-injury. It can be seen that for could be given to a return to unrestricted flying after a progress
severe head injury, within 12 mo of injury the risk of seizure is MRI. While the annualized risk of seizure may be higher than
approximately 5.8% (3.6 to 9.2%). This drops to 1.02% (0.51– the background population risk, the risks associated with this
2.10%) 1 to 4 yr after injury. SDH alone carries a rate ratio of 9.8
injury are thought to be small and mitigated by the patient’s
(3.6–27.1) after TBI, giving a overall risk of seizure of 0.6%
multicrew role.
(0.22–1.65%) per year.3
Using the data from Yeh et al.,25 even mild head injuries
carry a risk of PTE out to 4 yr post-injury. Table II uses this
ACKNOWLEDGMENTS
data to examine annualized risk. Here the risk of PTE after
severe TBI is approximately 1.46% (1.15–1.84%) in the first
Author and affiliation: Gordon G. Cable, P.G.Dip.Av.Med., FACAsM, Royal
Australian Air Force Institute of Aviation Medicine, RAAF Base Edinburgh,
year, but drops to 0.43% (0.29–0.65%) after 1–2 yr. The hazard
ratio of PTE associated specifically with SDH they found to be South Australia, Australia.
4.98, giving an annual risk of 0.3% per year. Therefore, it can
be seen in these tables that the mean annualized risk of seizure
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