INTRODUCTION
Subdural hematomas (SDHs) are subdural blood collections generally associated with acute head trauma, with or without associated fracture, which are concave in shape and approximate the contour of the adjacent cerebral hemisphere convexity [11]. They can be classified clinically and/ or radiologically as acute SDH (ASDH), subacute SDH (SSDH), and chronic SDH (CSDH). The clinical classification of SDH based on clinical history is as follows : acute (onset of trauma up to 3 days), subacute (4 to 20 days) and chronic (greater than 21 days) [16]. Radiologically, usually using computed tomography (CT) scan, ASDH are hyperdense lesions, presumed to have occurred within 2 days of trauma; CSDH are hypodense lesions presumed to have occurred beyond 2 weeks of the trauma; and SSDH are hyperdense to isodense lesions presumed to have occurred between 2 days to 2 weeks of trauma.
CSDH is defined as a liquefied hematoma in the subdural space with a characteristic outer membrane and occurring, if known, at least 3 weeks after head injury [1]. The most common theory of the cause of CSDH is a minor inertial brain injury causing movement of the brain within the skull and tears bridging veins as they traverse the cell layer of the dural border [15]. These CSDHs evolve from ASDH which may represent a spectrum of SDH [12].
The incidence of SDH is 24%. Specifically, the incidence of SSDH which is 0.89%, may have been underestimated due to its clinical imitation by CSDH [14]. The incidence of CSDH on the other hand is not well known but may range from 13 to 39 per 100000 persons [12].
The risk factors commonly implicated in SDH include : increasing age, alcohol consumption, male sex, use of anticoagulant or antiplatelet drugs, Alzheimer’s disease and other neurological diseases associated with brain atrophy, systemic disease associated with brain atrophy (e.g., liver and kidney disease), dialysis, conditions associated with craniocerebral disproportion (after ventriculoperitoneal shunting), conditions associated with low intracranial pressure (lumbar cerebrospinal fluid drainage and spontaneous intracranial hypotension, lumbar puncture, spinal anesthesia), spinal surgery complicated by dural tears [12]. CSDH, for which the mean age at occurrence is in the eighth decade, represents a growing problem in much of the developed world as the population ages. This demographic shift, together with the increasing use of anticoagulants and antiplatelet agents in older patients, complicates the management of these patients [8].
The management of each type varies considerably, with only the ASDH having a definite surgical guideline in the Traumatic Brain Injury Guidelines of The Brain Trauma Foundation [5]. Treatment for CSDH remains surgical; observation is recommended for affected patients with minimal or no symptoms. The three options for surgical drainage are the following : 1) burr hole drainage which can be performed with the patient under local or general anesthesia, usually in the operating room, 2) twist drill craniostomy which is usually performed with the patient under local anesthesia, at the patient’s bedside, and 3) open craniotomy which is done in the operating room [8]. The reoperation rate has been reduced to a range of 10% to 20% [4]. Meanwhile, SSDH has been poorly studied and documented. Surgical drainage may be indicated if SSDH is enlarging, or it becomes symptomatic [2].
This study investigated the surgical outcomes of patients with non-acute SDH among a group of elderly people aged 56 years old and above who were retired military personnel and were deemed physically fit and healthy during their younger active years (20’s to 50’s).
MATERIALS AND METHODS
Study design and time period
The charts reviewed for this study were from January 2016 to April 2019, in a subspecialty general hospital in the Philippines catering to military veterans. There were 35 patients with surgically managed sub-acute and CSDH in this period. However, only 21 of the patients were selected : all were retired military personnel, with ages greater than or equal to the retirement age of 56 years old, presumed previously physically and mentally healthy as required in the military. Data was gathered from hospital records, electronic database, census and charts. The authors retrospectively reviewed clinical and radiologic findings, surgical treatment and outcomes. Furthermore, the Victoriano Luna General Hospital Institutional Review Board (IRB No. 2024-24868) was obtained for this study and was stratified as a minimal risk protocol.
Operational definitions
Mixed-type SDHs (MSDHs)
MSDHs, a term proposed in this study, is defined as a mixeddensity hypointense and hyperintense subdural lesions on CT scan that have bright red blood/fluid intraoperatively, instead of the classic machine/engine oil fluid. Included in this MSDH category are the SSDH which are also mixed density subdural lesions that can coexist with CSDH.
Inclusion and exclusion criteria
The inclusion criteria are as follows : 1) all surgically managed non-acute SDH which are comprised of CSDH and MSDH. a) CSDH which are purely hypodense lesions on CT scan with an engine-oil or machine-oil brownish-red fluid seen intraoperatively, with or without a documented history of trauma more than 3 weeks. b) MSDH which are mixed hypodense and hyperdense subdural lesions on CT scan with non-machine oil fluid intraoperatively (i.e., bright red blood or fluid admixed with small clots) and with or without a history of trauma at 4 to 20 days. 2) Subjects are retired military personnel or veterans 56 years-old or older—the prescribed retiring age of veterans in the Philippines.
The exclusion criteria are as follows: 1) ASDH which are welldelineated intensely hyperdense, crescent-shaped subdural lesions on CT scan with a solid subdural blood clot seen intraoperatively, with onset of trauma up to 3 days. 2) Complicated intracranial pathology; with hematomas (epidural, intraparenchymal) other than a SDH. And 3) medically managed or conservatively managed SDH.
RESULTS
A total of 21 out of the 35 cases were included after application of the inclusion and exclusion criteria. Among the 21 patients, only 16 of their charts were secured and extracted for other information. For the remaining five charts, data were gathered from electronic databases/census. All patients were male. The age ranged from 56 to 90 years old, with a mean age of 69 years old. Eighteen of the patients were greater than 60-year-old, of which, three patients were in their 80s and two were in their 90s. Table 1 below summarizes the demographics and symptomatology observed among the 21 patients in this study.
Fourteen patients were diagnosed preoperatively with CSDH, seven were diagnosed with MSDH. Of the 14 patients with CSDH, postoperatively, nine patients were found to have the classic liquefied engine-oil like fluid (Fig. 1) on evacuation while the other five were found to have bright red fluid on dural opening suggesting a subacute bleed. On the other hand, six of the seven patients diagnosed with MSDH preoperatively were consistent to have bright red fluid output (Fig. 1) on initial evacuation. One respondent was post-operatively diagnosed to have CSDH after showing engine-oil like output. This brought the number of MSDH to 11 patients from the cohort. Table 2 summarizes the operative technique, intraoperative findings and post-op outcomes and diagnosis of the patients.
Of the 14 preoperatively diagnosed CSDH cases, six had a one-burr hole craniotomy with evacuation of hematoma while the other eight had a two-burr hole craniotomy with evacuation of hematoma. Of the seven cases of MSDH, all of which were unilateral, one underwent a formal fronto-temporo-parietal craniotomy with evacuation of MSDH with admixed clots, three underwent a one burr hole craniotomy while three underwent a two burr hole craniotomy.
Nineteen out of the 21 cases (approximately 90.47%) had improved outcomes immediately in the postoperative period while two were mortalities (mortality rate, 9.5%) from medical causes. The causes of the mortalities of the two patients were as follows : 1) acute myocardial infarction and 2) pneumonia with multiple comorbidities.
From the 17 retrieved charts, 10 patients had the Glasgow coma scale (GCS) 15 preoperatively and remained with the same GCS postoperatively. Nine of the aforementioned 10 patients had hemiparesis that improved to normal strength postoperatively. The other seven patients had GCS range of 10 to 14 with two patients improving to GCS 15. The other three patients improved to GCS 13-14. Five of the seven patients who had GCS <15 and survived improved their motor strength to 5/5 from hemiparesis. Of the known risk factors in literature, only three patients out of 17 (17.64%) had use of antiplatelet or anticoagulant (warfarin, aspirin, heparin) without history of trauma.
DISCUSSION
In a study by Tripathy et al. [14] in 2016, SSDH is believed to be a result of subdural effusion in the 1-3-week period. The collection of partly liquefied clot with resorbing blood products is surrounded on both sides by a “neomembrane” of organizing granulation tissue. This undergoes organization, lysis and neomembrane formation and within 2 to 3 days, the initial soft, loosely organized clot of an ASDH becomes organized. Breakdown of blood products and formation of organizing granulation tissue change the imaging appearance of SSDH. These are crescentic fluid collections that are iso to slightly hyperdense in CT scan. However, FLAIR sequence magnetic resonance imaging is the most sensitive sequence for detecting SSDH as the collection is typically hyperintense [14].
A study by Balser et al. [3] evaluated the effectiveness and efficacy of delayed burr hole surgery in relation to reduction of postoperative SDH volume in patients with ASDH. The mean delay to surgery was 13.9±7.5 days which practically coincides with a clinical classification of SSDH or CSDH. The outcome of the study showed that delayed burr hole surgery is generally effective for reduction of SDH volume at the late subacute to chronic stage.
There is no clear consensus regarding appropriate treatment in MSDH and CSDH. Time of trauma onset to burr hole surgery in patients with late subacute or chronic stage maybe important in decreasing recurrence risk [4]. Patients diagnosed with late SSDH or CSDH treatable by burr hole surgery should not be deferred when an operation is required [7]. In this study, the preoperative diagnosis for both CSDH and MSDH are dependent on the pre-operative scans while the final diagnoses are based on the intraoperative findings upon evacuation of the hematoma. In addition, it was observed that nine out of 11 CSDH patients attained the Glasgow outcome scale extended (GOS-E) score of eight while all the respondents in the MSDH group attained the same GOS-E score. This indicates that early surgical intervention in patients with non-acute SDH is beneficial to attain a favorable GOS-E. Moreover, the outcomes of both MSDH and CSDH are comparable with low mortality rate (approximately 9.5%) and immediate postoperative improvement (approximately 90%).
Of the patients in this cohort that had non-acute SDH, only seven had history of trauma. Both MSDH and CSDH are classified under non-acute SDH. They differ on the CT scan appearance, duration of trauma and post-operative findings. MSDH usually appear with mixed density images that range from hypodense to hyperdense lesions that may or may not have history of trauma. On the other hand, classic CSDH have a uniform hypo-to-isodense cresenteric lesion that may be precipitated with a traumatic head injury that occurred at least more than 21 days.
Demographic characteristics
When focusing on non-acute SDH, the data showed a similar mean age at 69 years old which occurs earlier than in the developed world which is on the eighth decade [8]. Majority of patients in this study were 70 or younger; only five of the 21 patients were aged 80-90’s.
Being in a developing country may have contributed to the relatively younger incidence in this population. Among risk factors implicated, only increasing age and male sex have been seen in the data. Another possibility could be that trauma is more frequent in a developing country especially in the nature of military activity. Whether prior military work contributes to earlier development of cerebral atrophy, a risk factor for SDH, can only be hypothesized.
Diagnosis : clinical vs. radiologic
This seeming discordance in preoperative, intraoperative, and postoperative diagnoses as shown in Table 2 may reflect the differences in the time frame between clinical and radiologic classifications. This also raises concern over which classification, clinical or radiologic, should be used. The preoperative diagnosis is crucial since it greatly affects decision making in the urgency and type of surgery. Further mix-up occurs when there are cases that are CSDH with acute to subacute components (Fig. 2). It is important to remember that most patients are unaware or are unable to recall of the onset of trauma, hence the radiologic classification was relied upon in this study, especially when clinical information is lacking or inconsistent. Despite the pre-operative diagnosis being reliant on pre-op CT scan, the final diagnoses were still dependent on the intraoperative findings of non-acute SDH, which was liquefied blood regardless of color of the fluid output.
Management and outcomes
Based on this study, non-acute SDH (CSDH and MSDH) despite its clear differences, both entities are treatable by burr hole surgery. Fig. 3 shows the proposed algorithm elucidated based on the cohort reviewed. Tripathy et al. [14], said that the management of SSDH is often equated clinically with CSDH. In the same study, even ASDH and SSDH have characteristics that superimpose with glaring differences. The differences are as follows : 1) SSDH develops in the elderly with trivial trauma or minor head injury, 2) there is a relatively long periods of clear consciousness, 3) patients have heavy alcohol abuse history with a high risk of hypertension and diabetes, 4) brain CT finding, done 5-7 days after trauma, reveal a mixed density findings, and 5) outcome is poor when there are systemic comorbidities.
Meanwhile, surgical evacuation remains to be the gold standard for treatment of symptomatic CSDH [13]. Various surgical options have been mentioned including twist-drill, burr hole and craniotomy with the less invasive procedure having the greatest recurrence rate. In this current study, the term “burr hole craniotomy” pertains to a burr hole craniostomy with enlargement of the craniostomy site to a size from 1cm to 2.5 cm for larger exposure [9,10]. The data showed one recurrence of the 22 cases, a rate of 4.5%, for any of the procedures which is lower that in literature which is at 8-33% recurrence [6].
In a study of Yokosuka et al. [16], which explores the safety and efficacy of endoscopic approaches, stated that a large craniotomy or craniectomy is the first choice for both ASDH and SSDH. This study mentioned however that burr hole surgery had good outcomes.
The diagnoses were mostly based on the written clinical data and diagnosis, which used radiologic impressions, by the clinician. In other words, official radiologic impressions and results were not necessarily utilized. A correlation with MSDH and CSDH and their corresponding imaging findings (Hounsfield units, thickness, midline shift, etc.) would have added significant information as to the differences between these two seemingly similar entities.
Lastly, a larger cohort could have been observed at longer time interval to further compare the outcomes of the intervention among this population using the GOS-E scale.
CONCLUSION
The classification of MSDH and CSDH as non-acute SDH, whether clinical and radiologic, seems to be an academic exercise for clinicians since, based on the results of this paper; its management and subsequent outcomes are similar. Grouping them under the collective term of non-acute SDH could be an acceptable nomenclature for SDH for which burr hole surgery remains to be a feasible, safe, and effective option for these patients.
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