Key points

Introduction

Chronic subdural hematomas are a common pathologic condition, especially of the elderly. These lesions can at times be managed medically without surgical intervention if they are small with minimal mass effect and if the lesions are not significantly symptomatic. At other times, they require surgical intervention for symptomatic relief and/or avoiding mortality.

Multiple surgical methods have been described, including bedside twist drill trephination, formal burr hole trephination, craniotomy with resection of neomembranes, and subdural-peritoneal shunt placement. All of these techniques may or may not involve irrigation of the subdural space, and both burr hole and craniotomy techniques may or may not involve temporary postoperative closed-system drainage. Single or double burr hole evacuation with or without postoperative closed-system drainage has been proven to successfully treat these lesions and is the most common method used.

However, hematomas can recur. Recurrence can be defined as any radiologic recurrence, which can be asymptomatic, mild to moderately symptomatic recurrence requiring medical management, or severely symptomatic recurrence requiring surgical evacuation. The rate of clinically significant recurrence that requires surgical evacuation ranges from 7.0% to 26.5% after initial burr hole evacuation with or without postoperative closed-system drainage. Over all types of initial operations, the rate ranges from 2% to 37%. The average time from initial operation to the second one ranges from 6 days to 3.5 weeks after the first operation.

Introduction

Chronic subdural hematomas are a common pathologic condition, especially of the elderly. These lesions can at times be managed medically without surgical intervention if they are small with minimal mass effect and if the lesions are not significantly symptomatic. At other times, they require surgical intervention for symptomatic relief and/or avoiding mortality.

Multiple surgical methods have been described, including bedside twist drill trephination, formal burr hole trephination, craniotomy with resection of neomembranes, and subdural-peritoneal shunt placement. All of these techniques may or may not involve irrigation of the subdural space, and both burr hole and craniotomy techniques may or may not involve temporary postoperative closed-system drainage. Single or double burr hole evacuation with or without postoperative closed-system drainage has been proven to successfully treat these lesions and is the most common method used.

However, hematomas can recur. Recurrence can be defined as any radiologic recurrence, which can be asymptomatic, mild to moderately symptomatic recurrence requiring medical management, or severely symptomatic recurrence requiring surgical evacuation. The rate of clinically significant recurrence that requires surgical evacuation ranges from 7.0% to 26.5% after initial burr hole evacuation with or without postoperative closed-system drainage. Over all types of initial operations, the rate ranges from 2% to 37%. The average time from initial operation to the second one ranges from 6 days to 3.5 weeks after the first operation.

Patient-specific risk factors

Given the high recurrence rate after subdural hematoma evacuation, a thorough understanding of risk factors leading to such recurrence is paramount. Risk factors for subdural hematoma recurrence can be split into 3 groups: first, patient factors, such as age, sex, comorbidities, alcohol abuse, anticoagulant and/or antiplatelet use, brain atrophy, bleeding tendency, or intracranial hypotension; second, subdural hematoma factors, such as hematoma size and location, presence of membranes, and acute versus chronic; and third, surgical factors, such as timing of surgery, single burr hole versus multiple burr holes versus craniotomy, irrigation, and drainage.

Commonly associated risk factors are chronic alcoholism; well-known predisposing factors include shunt procedures leading to intracranial hypotension ( Fig. 1 ), seizure disorders, and impaired coagulation. Oishi and colleagues performed a retrospective review of 116 patients and found in their recurrence group a significantly lower incidence of head injury and significantly lower interval from symptom onset to hospitalization. Jung and colleagues performed a retrospective review of 182 patients and found a significant clinical history risk factor was hemiparesis. Diabetes mellitus trends toward increased recurrence in some studies ; however, it has no significance in others. Yamamoto and colleagues found a higher recurrence rate in the absence of diabetes mellitus.

( A ) Immediate postoperative computed tomography scan after ventriculoperitoneal shunt placement. ( B ) Delayed presentation of bilateral subdural hematomas, trabecular or multi-loculated type on the right. ( C ) After waiting for a short number of days, the subdural hematoma grew more hypodense, appearing as the separated or layered type. The patient then underwent burr hole evacuation. ( D ) Immediately after burr hole evacuation, note the poor brain reexpansion and significant subdural air. ( E ) Recurrence of hematoma, appearing as the homogeneous, hypodense type. ( F ) Repeat burr hole evacuation lead to complete resolution.

Clearly, further studies are needed to delineate medical comorbidities that predispose to recurrence.

Most studies have found no difference in recurrence rate in terms of age, sex, hypertension, heart disease, antiplatelet or anticoagulant use, or cause of hematoma (trauma vs unknown vs after craniotomy).

Radiologic risk factors

Radiographic factors involved in postoperative recurrence rate include hematoma location in convexity versus skull base; internal architecture as proposed by Nakaguchi and colleagues (homogenous density [high, low, or isodense], laminar [mixed density], separated [known as layered] including gradation subtype, and trabecular [multi-loculated] [see Fig. 1 ]); unilateral versus bilateral; midline shift; width of subdural space; subdural hematoma volume; and presence of air.

Poor reexpansion of the brain after hematoma evacuation has been extensively studied as a predisposing factor for recurrence (see Fig. 1 D). Mori and Maeda analyzed 500 cases of burr hole evacuation of subdural hematomas with closed-system drainage and found that brain reexpansion at 1 week occurred in 45% of patients with recurrence and 55% without recurrence ( P <.001). They identified age greater than 70 years, preexisting cerebral infarction, and persistent subdural air as significant correlates of poor brain reexpansion ( P <.001). The presence of substantial subdural air hinders reduction of the cavity created by hematoma evacuation and increases the recurrence rate (see Fig. 1 D).

Poor brain reexpansion is related to high brain surface elastance, which is correlated with greater age, fibrous organization of subdural neomembranes, and impaired cerebral blood flow. Fukuhara and colleagues analyzed the relationship between brain surface elastance and hematoma recurrence by evacuating hematomas via burr holes, placing a Muller ophthalmodynamometer on the brain surface and compressing the brain to 5 mm Hg. They then measured the depth required to reach this pressure (which they defined as the brain elastance). They found that those who had a subdural space greater than 3 mm 1 month postoperatively, relative to those with less than 3 mm, had a significantly higher brain surface elastance (ie, their brain could be compressed to a greater depth until 5 mm Hg pressure was reached). They found some correlation between age and elastance, no correlation between volume of hematoma and elastance, and a tendency for those with high-density hematomas and more symptomatic patients (drowsy and/or neurologic deficit or worse) to be correlated with elastance, although this correlation was nonsignificant. They suggest that high brain elastance leads to poor brain reexpansion and can predispose to recurrence; thus, measuring brain elastance can be a tool to help predict recurrence.

Markwalder and colleagues studied the relationship between subdural pressure, intracranial pressure, and brain reexpansion postoperatively and found that brain reexpansion was promoted by higher subdural (>25 cm H ₂ O) and intracranial pressures and inhibited by a thick fibrotic neomembrane.

With regard to the hematoma’s internal architecture, the recurrence rate is generally lower in the homogeneous type and significantly higher in the separated type, including gradation subtype (see Fig. 1 C, E). Within homogeneous types, the recurrence rate was significantly lower in the low-density subtype relative to other types. Oishi and colleagues found a higher rate of recurrence in patients who had any component of hyperintensity on preoperative computed tomography (CT) scan, suggesting a more acute hematoma, 15.6% versus 1.7% (see Fig. 1 B). The investigators suggest this may be an indication of vulnerable capillaries within a neomembrane, which forms secondary to inflammation induced by the blood itself. Nakaguchi and colleagues theorize that this may be secondary to the limited organization of the younger hematoma (immature fibrosis of the neomembranes or trabeculae). Oishi and colleagues suggest postponing surgical evacuation, unless emergent, until the hematoma appears isodense or hypodense on CT scan. (However, it must be noted that these cases were performed with single burr hole surgery; thus, any acute, clotted blood may have not been evacuated.)

Subdural hematomas can recur ipsilaterally or contralaterally. Thin subdural hematomas on the contralateral side are a high risk of recurrence contralaterally. Bilateral hematomas are significant risk factors for recurrence.

It was also significantly higher with greater midline shift (>5 mm in one study, >10 mm in another) and the presence of acute clots (which were only seen postoperatively in cranial base subdural hematomas). There is a higher correlation of recurrence with maximum width of subdural space greater than 10 mm.

Stanisic and colleagues found that preoperative subdural hematoma volume of less than 115 mL and postoperative volume of less than 80 mL were strongly correlated with no recurrence (94.4% and 97.4% respectively). On the other hand, Huang and colleagues found no significance of hematoma volume on recurrence rate.

Surgical risk factors

As noted previously, there are multiple operative techniques currently used to evacuate chronic subdural hematomas. Weigel and colleagues did a systematic review of literature and compared multiple different techniques, including twist drill craniostomy (hole diameter up to 5 mm), burr hole craniostomy (hole diameter up to 30 mm), and larger openings, such as craniotomies. They found most studies used one of these 3 methods with or without irrigation and with or without postoperative closed-system drainage. Craniotomies had a morbidity rate of 12.3%, mortality rate of 4.6%, and recurrence rate of 10.8%. In contrast, twist drill craniostomies and burr hole craniostomies, respectively, had a morbidity rate of 3.0% and 3.8%, mortality rate of 2.9% and 2.7%, and recurrence rate of 33.0% and 12.1%. The differences in mortality rates were not significant, whereas craniotomy techniques had significantly higher morbidity than twist drill or burr hole techniques; recurrence rates were significantly lower in craniotomy and burr hole techniques relative to twist drill craniostomy techniques. It is important to note that the studies comparing these techniques are not controlled randomized trials and, thus, the patients selected for craniotomy may have been those suspected to have a higher morbidity or probability of recurrence.

Commonly, a closed-system drainage tube is used several days postoperatively. Markwalder and Seiler performed a case series of 21 patients and found progressive clinical improvement when closed-system drainage was used. Wakai and colleagues did a prospective study on 38 patients and also found a lower recurrence rate when closed-system drainage used: 33% versus 5%. Santarius and colleagues did a randomized controlled trial evaluating recurrence rate of subdural hematoma after evacuation with and without drain placement. The trial was stopped early because of a significant benefit of drain placement with 9.3% recurrence with drain and 24% without. Weigel and colleagues also compared twist drill craniostomy with and without drainage and found a significantly lower recurrence rate with drainage.

Kwon and colleagues analyzed 175 patients who underwent burr hole trephination with closed-system drainage for 5 days and found a significantly higher recurrence rate in patients who had less than 200 mL of drainage volume postoperatively relative to those who had more than 200 mL.

Jung and colleagues found no difference in recurrence rate with one versus 2 burr holes or location of drainage tube (none, frontal, occipital, or parietal). Others, on the other hand, have found a significantly lower recurrence rate when the tip of the drainage tube was in a frontal position as opposed to temporal, occipital, or parietal.

Commonly, patients are kept in a flat, supine position postoperatively to decrease the recurrence rate. Abouzari and colleagues evaluated 84 patients who underwent single burr hole trephination for evacuation and irrigation of chronic traumatic subdural hematoma and postoperative closed-system drainage. They randomly assigned the patients into 2 groups: one that was placed in a supine, flat position for 3 days postoperatively and the other placed with the head of the bed elevated to 30° to 40° for the same time frame. They defined recurrence via clinical or radiologic criteria and found a significantly higher rate in those patients sitting with the head elevated relative to those kept flat. However, only one of these recurrences in the former group was significant enough to require reoperation. There were no significant differences in terms of complications from lying flat, such as atelectasis and/or pneumonia. On the other hand, Nakajima and colleagues found no difference in recurrence rates with the same trial design as Abouzari and colleagues.

Some surgeons stress irrigation of the subdural space to remove as much subdural fluid and/or acute clots as possible and replace it with saline or lactated Ringer solution. Lee and colleagues compared 2 groups retrospectively: one in which a subdural catheter was placed via burr hole trephination and saline instilled until the fluid exuded clear and a second group in which a subdural catheter was placed but no irrigation was performed. Both groups underwent postoperative closed-system drainage for at least 48 hours. These investigators found a significantly lower rate of recurrence with irrigation than without in a group who underwent burr hole craniostomy and postoperative closed-system drainage.

Ishibasi and colleagues retrospectively compared a group with burr hole drainage only (in which a single burr hole was placed with postoperative closed-system drainage) to a group with burr hole drainage with irrigation and found a significantly higher recurrence rate in the drainage only group (10.3% vs 2.9%).

On the other hand, Okada and colleagues had the opposite results. These investigators compared 2 groups: irrigation and drainage. The irrigation group had a subdural catheter placed via a burr hole and the hematoma was irrigated until the fluid exuded was clear. The drainage group had a catheter placed in the subdural space and was drained at a slow rate postoperatively. The drainage group had a significantly lower rate of recurrence (5% vs 25%). Kuroki and colleagues also compared 2 groups, one in which a subdural catheter was placed without irrigation and taking care not to introduce air into the subdural cavity and another group in which the subdural space was irrigated and then a catheter was placed (the subdural space was filled with saline on closure with the burr hole at the highest point to introduce as little air as possible). The drainage group without irrigation had a significantly lower rate of recurrence (1.8% vs 11.1%), lower duration of drainage, and faster disappearance of hematoma. Given the conflicting results of irrigation, a randomized controlled trial would be necessary to further elucidate the role of intraoperative irrigation on recurrence rates.

Ram and colleagues and Hennig and Kloster evaluated the significance of postoperative continuous inflow and outflow irrigation and drainage. Ram and colleagues found a significantly lower rate of recurrence with continuous postoperative irrigation. Hennig and Kloster compared 4 groups: burr hole craniostomy with continuous inflow and outflow drainage postoperatively for up to 48 hours, burr hole craniostomy with intraoperative irrigation and postoperative closed-system drainage, burr hole craniostomy with intraoperative irrigation only, and craniotomy. They found a significantly lower rate of recurrence in the continuous drainage group, 2.6%, relative to the other groups (23.8%, 32.6%, 44.4%, respectively). These findings suggest that although intraoperative irrigation has an uncertain impact on recurrence, postoperative continuous irrigation and drainage can lower it.