This article discusses the epidemiology and natural history of chronic subdural hematoma (CSDH), a common disease prevalent in the elderly population. The incidence of CSDH ranges from 1.72 to 20.6 per 100,000 persons per year. Risk factors include advancing age, male gender, and antiplatelet or anticoagulant use. Clinical progression is separated into 3 distinct periods, including the initial traumatic event, the latency period, and the clinical presentation period. The recurrence of CSDH and nonsurgical predictive factors are described in detail to provide a comprehensive understanding of the outcome of this disease.
Key points
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Chronic subdural hematoma (CSDH) is a common disease that is prevalent predominantly in elderly patients.
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The incidence of CSDH ranges from 1.72 to 20.6 per 100,000 persons per year.
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Clinical progression of CSDH has 3 stages: initial formation, latency, and clinical presentation.
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Risk factors for CSDH include advancing age, male gender, and antiplatelet or anticoagulant use.
Introduction and overview
Chronic subdural hematoma (CSDH) is a common disease characterized by the abnormal collection of blood products in the subdural space with a relatively indolent course of disease progression. The overall incidence of CSDH was reported to range from 1.72 to 20.6 per 100,000 persons per year, with an incidence that is significantly higher in the elderly. A trend toward an increase in incidence has been observed, and may be attributed to the overall aging population resulting from an increase in life expectancy. The formation of CSDH remains unclear, and the pathophysiology has been hypothesized to be triggered by inflammatory responses, transformation from acute subdural hematoma, or an increased osmotic oncotic pressure gap between the hematoma and blood vessels. Additionally, subclinical brain injury resulting in minor trauma to bridging veins may also facilitate the chronic accumulation of blood within the hematoma encapsulated by neomembranes.
Manifestations of CSDH are variable, and mainly caused by immediate intracranial compression through expansion of the hematoma. Presenting symptoms include headaches, seizure, mental status changes, weakness, sensory disturbance, dysarthria, gait disturbance, nausea and vomiting, stroke, and coma. In patients presenting with CSDH, 3% to 20% present with comatose status, and severe impairment with brain herniation may occur in 2% of cases. Of note, 10% to 30% of patients were also on anticoagulation or antiplatelet therapy. CSDH can be diagnosed quickly using computed tomography, showing a crescent-shaped mass with a slight hypodensity representing the fluid sac of hematoma encased by the neomembranes. Increased density and heterogeneous density may be noted as a natural progression of the disease or if recent bleeding is present.
Surgical evacuation of the hematoma remains the mainstay of treatment for symptomatic patients with diagnosed CSDH. Access to the hematoma capsule is approached through twist drill openings or burr hole openings; craniotomy is reserved generally for extensive hematoma, and is considered as a second-tier surgical option for most cases. For asymptomatic patients, nonsurgical management is preferred, which includes eliminating precipitant factors such as anticoagulation or antiplatelet medications, correction of underlying coagulopathy, and symptom management. Prognosis after surgical treatment has been favorable in most reported series, with 80% to 90% of treated patients achieving a satisfactory outcome at follow-up, with mortality reported to be low at 0.5% to 4.3%. Noticeably, the recurrence of CSDH may be as high as 70%, but only 10% to 20% of recurred CSDH require reoperation.
Introduction and overview
Chronic subdural hematoma (CSDH) is a common disease characterized by the abnormal collection of blood products in the subdural space with a relatively indolent course of disease progression. The overall incidence of CSDH was reported to range from 1.72 to 20.6 per 100,000 persons per year, with an incidence that is significantly higher in the elderly. A trend toward an increase in incidence has been observed, and may be attributed to the overall aging population resulting from an increase in life expectancy. The formation of CSDH remains unclear, and the pathophysiology has been hypothesized to be triggered by inflammatory responses, transformation from acute subdural hematoma, or an increased osmotic oncotic pressure gap between the hematoma and blood vessels. Additionally, subclinical brain injury resulting in minor trauma to bridging veins may also facilitate the chronic accumulation of blood within the hematoma encapsulated by neomembranes.
Manifestations of CSDH are variable, and mainly caused by immediate intracranial compression through expansion of the hematoma. Presenting symptoms include headaches, seizure, mental status changes, weakness, sensory disturbance, dysarthria, gait disturbance, nausea and vomiting, stroke, and coma. In patients presenting with CSDH, 3% to 20% present with comatose status, and severe impairment with brain herniation may occur in 2% of cases. Of note, 10% to 30% of patients were also on anticoagulation or antiplatelet therapy. CSDH can be diagnosed quickly using computed tomography, showing a crescent-shaped mass with a slight hypodensity representing the fluid sac of hematoma encased by the neomembranes. Increased density and heterogeneous density may be noted as a natural progression of the disease or if recent bleeding is present.
Surgical evacuation of the hematoma remains the mainstay of treatment for symptomatic patients with diagnosed CSDH. Access to the hematoma capsule is approached through twist drill openings or burr hole openings; craniotomy is reserved generally for extensive hematoma, and is considered as a second-tier surgical option for most cases. For asymptomatic patients, nonsurgical management is preferred, which includes eliminating precipitant factors such as anticoagulation or antiplatelet medications, correction of underlying coagulopathy, and symptom management. Prognosis after surgical treatment has been favorable in most reported series, with 80% to 90% of treated patients achieving a satisfactory outcome at follow-up, with mortality reported to be low at 0.5% to 4.3%. Noticeably, the recurrence of CSDH may be as high as 70%, but only 10% to 20% of recurred CSDH require reoperation.
Epidemiology
The incidence of CSDH has only been reported sporadically throughout the years. In a Finnish study conducted by Foelholm and Waltimo in 1967, 64 residents of the city of Helsinki diagnosed with CSDH were included over a 7-year period, rendering an overall incidence of 1.72 per 100,000 persons per year. The authors highlighted a significant increase of incidence of up to 7.35 in the elderly population of 70 to 79 years of age. After this study, Kudo and colleagues examined the incidence of CSDH in the Awaji island of Japan from 1986 to 1988, and concluded an overall incidence rate of 13.1 per 100,000 persons per year, with an incidence of 3.4 in the population under 65 years old and 58.1 in the elderly. A North Wales study by Asghar and colleagues including patients between 1996 and 1999 revealed a lower incidence rate of 8.2 per 100,000 persons per year in patients greater than 65 years of age. In contrast, another Japanese study examining incidence of CSDH between 2005 and 2007 used data from a national registry. The authors reported an increased incidence of CSDH of 20.6 per 100,000 persons per year, with 76.5 in the 70 to 79 age group and 127.1 in the 80 years old age group. Additionally, in a recent study by Balser and colleagues focusing on the veteran population in United States, an overall incidence rate of 79.4 per 100,000 persons per year was observed, with age-standardized rate at 39.4 per 100,000 persons per year.
From these studies, it seems that the incidence of CSDH has been increasing over the years, with the increasing risk of CSDH attributable to the aging population and the increasing prevalence of anticoagulation/antiplatelet medication use in general populations. However, the interpretation of the reported incidence rate should be managed with caution. To date, there are only 2 epidemiologic studies examining overall incidence of CSDH in a relatively closed population with low migration rates—the Finnish study and the Awaji island study in Japan—and a considerable difference in incidence rate has been noted between these 2 studies. Although the difference has been generally explained by increasing incidence of CSDH over the 20-year interval between these 2 studies, the examined populations are heterogeneous, and confounding factors associated with population differences may also modify significantly the risk of CSDH. For instance, the incidence of traumatic brain injury, which is considered one of the precipitating factors for development of CSDH, is generally low in Finland, and may account for the lower rate of CSDH in the Finnish population. According to a nationwide, population-based study in Finland examining total traumatic brain injury from 1991 to 2005, the overall incidence was 101 per 100,000 persons per year, significantly lower than that reported in other countries, including the Netherlands, Estonia, and New Zealand. In the veteran study where traumatic brain injury within the included population is considered highly prevalent, the projected incidence rate of CSDH was reported to be 121.4, which is significantly higher than that of the general population in other studies; conversely, in the same study, the prediction of CSDH incidence was only 17.4 in civilian-based models. Additionally, in a study reported by Baechli and colleagues examining the prevalence of CSDH in a large single-center study in Switzerland during a 7-year interval (1996–2002), the annual incidence remained relatively constant. Therefore, whether the global incidence of CSDH is truly increasing warrants cautious consideration, and the trend of an increased incidence for CSDH should be adjusted for population and environmental differences for accurate interpretation.
Natural history and risk factors
Origin of Chronic Subdural Hematoma
Numerous theories have been proposed regarding the pathogenesis of CSDH. Virchow first related the origin of CSDH to an inflammatory response of the brain in 1857, in which he described a case of “pachymeningitis hemorrhagic interna,” and noted a membranous structure in the inner surface of the dura believed to be the inflammatory origin for hematoma formation. In contrast, Trotter favored a hematoma first etiology and suggested that the role of trauma in the development of CSDH. Putnam and Cushing, recalling a traumatic component in patients from both of their experiences, supported this theory by proposing the cause of CSDH to be originated from “an apparently insignificant trauma to the head,” and indicated that the neomembranes formed in these cases “differs from that of the commonly described pachymeningitis hemorrhagica interna.” In a later review of the topic, Holmes summarized all patients with diagnosis of CSDH in 3 Chicago hospitals between 1914 and 1925, and revealed that trauma is the factor in both cases of intraoperatively confirmed CSDH. The traumatic theory attributed the formation and expansion of hematoma to insignificant or repeated subclinical trauma. The fluid collection was hypothesized to be of vascular origin, either from transformation of asymptomatic acute hematoma, or microbleeding from neoformed vascular structures or torn bridging veins after trauma.
In contrast with theories suggesting the expansion of the hematoma through rupture of vessels, Gardner and Zollinger and their colleagues indicated that increased osmotic oncotic pressure owing to blood product breakdown within the hematoma capsule may be the major underlying mechanism for hematoma enlargement following initial hematoma formation. However, this theory was not supported by later studies by Weir, who noted no difference between the oncotic osmolality of subdural hematoma and cerebrospinal fluid or venous blood. Lee also proposed that certain CSDHs may arise from incomplete resolution of acute subdural hematomas. In more recent studies, transformation of chronic subdural hygromas complicated with repeated ruptures in fragile neovascularized vessels into CSDH is believed to be the major pathway of CSDH formation.
Clinical Progression of Chronic Subdural Hematoma
The clinical progression of CSDH can be generally categorized into 3 periods: the initial period of traumatic event, the latency period of hematoma expansion, and the clinical period of CSDH manifestation. The initial period may present as either 1 or multiple clinical or subclinical traumatic events causing the initial formation of the hematoma, which is referred as the “seed” for CSDH development. Immediately after the initial phase is the latent phase, in which the hematoma matures slowly and increases in volume. The neomembrane formation on the dural side as well as on the arachnoid side facilitated the encapsulation of the hematoma, and was potentially the source of microhemorrhages owing to fragility of vessels formed by extensive neovascularization. The hyperactivation of the fibrinolytic system has also been proposed to play a role in the extension of hematoma. During this period, patients may be asymptomatic, and this may last for weeks to years. After the latency period, progressive decompensation of intracranial capacity occurs as a result of continuous growing of the hematoma capsule, and a constellation of symptoms may appear from increased intracranial pressure. At clinical presentation, approximately 10% to 20% present with seizures, 2% to 15% with coma, and 2% with brain herniation. Of note, less than 1% of all reported cases were discovered incidentally. Without any treatment, few CSDHs have been reported to regress spontaneously, whereas 40% of all patients may eventually recover on medical management without surgical intervention. However, 20% of patients undergoing conservative management experience clinical deterioration and require surgical intervention.
Risk Factors for Chronic Subdural Hematoma
It is evident in the literature that CSDH is not a static disease, and the risk of development, progression, and recurrence of CSDH may be modified significantly by several risk factors. Among all risk factors identified to date, the association of older age with risk of CSDH occurrence has been consistently described by existing literature. Epidemiologic studies reported significant increase in incidence of CSDH in the elderly compared with other age cohorts ; in addition, most CSDH case series also reported their cohort to be composed of patients with advanced age at mean age of 55 to 60 years, with some greater than 70 years of age. The underlying reason for greater prevalence of CSDH among the elderly is not completely understood, but may be attributed to a higher risk of falls in this population. In a study conducted by Baechli and coauthors including 354 consecutive CSDH patients, 69% of all patients were more than 65 year os age, and falls were reported in 77% of the cohort. Although the authors highlighted a trend toward a greater risk of falls in the elderly with a relative risk of 1.11, however, the result did not attain significance.
Male gender was also recognized to be a potential risk factor for CSDH. The Finnish epidemiologic study on the incidence of CSDH demonstrated an overall higher incidence for men over women. This trend was unchanged in the same cohort after stratification by age. Similarly, a male gender predominance of the incidence and prevalence of the disease was also observed in other CSDH studies. The difference in gender distribution of CSDH might not be related to falls; in 1 study, the risk of fall was reported to be similar between the 2 gender groups. However, the authors also noted that male gender may have been more likely to be exposed to injuries or other CSDH-related factors in general. This assumption is corroborated by discovery of CSDH-associated factors with a known male predominance, such as alcohol use and epilepsy. Male gender was also reported to bear a higher rate of recurrence after treatment for CSDH.
Aside from demographic risk factors, anticoagulation or antiplatelet therapy was also considered a risk factor for occurrence, as well as recurrence of CSDH. Because most patients with CSDH were elderly, an increased proportion of patients on anticoagulant agents for the prevention or treatment of systemic diseases is superimposed. Rust and colleagues observed 81 cases of CSDH in 2001 and 2002 within a defined population of 460,000 to 473,252 in Tasmania, Australia. The total number of patients taking warfarin in both years were collected from national insurance database, and the incidence of CSDH in patients on warfarin was noted to be 0.08% to 0.40% per year, compared with 0.002% to 0.010% per year in those without warfarin, rendering a greater than 40 times higher risk of CSDH development in warfarin users. Besides occurrence of CSDH, both anticoagulant and antiplatelet agents were also proposed to be associated potentially with the expansion of hematoma. The association of both medications with recurrence of CSDH was less clear and has been reported to be irrelevant in many studies.
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