CSDH is encountered more in elderly patients, commonly preceded by a recent history of head trauma, possibly trivial and unnoticed, usually between 3 to 4 weeks prior to presentation.
It seems the annual incidence of CSDH has been rising steadily over the past years. Lind and colleagues  reported an annual incidence of CSDH of 4.6 per 100,000 in 2003, in contrast to Cousseau and colleagues  who reported an annual incidence of 3.1 per 100,000 in 2001. This could be attributed to the rise in the older population with the medical technology development .
Various types of managements for CSDH are used including both conservative and surgical treatment; while conservative management is usually considered for completely asymptomatic cases, those with a small hematoma or moribund patients with significant co-morbidities, yet the literatures support the agreement that the surgical management is ideal for symptomatic CSDH [20, 26]. Surgical approaches include burr hole craniostomy with or without drainage, twist-drill craniostomy with or without drainage, and craniotomy [6, 9, 21]. However, the ideal surgical technique remains controversial.
Considering the fact that most of the CSDH patients are among the fragile geriatric group, it is preferred to choose both the suitable and at the same time the least invasive technique for surgical intervention aiming at minimizing the surgical manipulations to reduce the incidence of complications, enhance recovery and reduce recurrence rate.
Recently, burr hole craniostomy has been supported in literature as the gold standard for surgical treatment of CSDH, a simple technique having an equivalent outcome as compared to craniotomy, but with significantly lower mortality and morbidity and a shorter hospitalization period .
Our study was conducted on 30 patients with symptomatic unilateral or bilateral chronic unilocular subdural hematoma as confirmed on preoperative CT scan and/or MRI to whom evacuation through single-burr hole craniostomy and closed-system drainage was performed and assessed.
The mean age of our study cases was 67.37 years. Several studies attributes this to the common pathological changes occurring around this age group ; there was a male predominance as of 60% males and 40% female patients. Some studies suggested that the frequently encountered male predominance could be due to the more vulnerability to trauma [5, 15].
On evaluating the clinical outcome in our study, the GCS of the studied cases has shown a statistically highly significant improvement throughout the follow-up intervals (p = 0.001) in comparison to the preoperative values, and a statistically significant value on comparing the preoperative values to those on the first postoperative day (p = 0.024). Similarly, 25 (83.3%) the Markwalder score values significantly improved 1 month after surgery, there was a statistically highly significant improvement regarding the Markwalder score on comparing the preoperative values to those 1 month postoperatively (p = 0.001).
Mersha and colleagues  stated that 95.9% of their study patients had good recovery, GCS 4 or GCS 5, by the end of their follow-up period, and there were 2% deaths. This was similar to another Dakurah and colleagues  study done in Accra, Ghana, where 93.8% had good recovery with a mortality rate of 2.0%.
Also, our study recorded a statistically highly significant improvement on comparing the preoperative motor power of our study cases presented with limb weakness to those recorded 1 month after surgery (p = 0.004).
While our results denoted no statistically significant difference regarding the final study outcome on comparing patients presented with motor weakness to those who had no motor power affection before surgery, Mersha and colleagues  described a statistically significant association between presence of preoperative extremity weakness and postoperative outcome with P-value of 0.042; they also reported a shorter mean hospital stay of 3.68 ± 2.6 days in comparison to our study result of 6.59 ± 2.46 days.
We found also that over 36.7% of the participants had a midline shift between 10 and 15 mm on the preoperative CT scan/MRI, while 13.3% had a midline shift above 15 mm. There was an association between midline shift more than 15 mm and preoperative motor weakness (p = 0.04), however, no statistical significance was noted between other presentations and the midline shift.
The mean operative time in our study was 41.7 min (ranging from 33 to 75 min), which is another advantage for the used approach. This surgical time was close to that recorded by Salama  (35 min), and Guzel and colleagues  (36.4 min).
Our study reported a single case (3.7%) of CSDH recurrence that was successfully managed through a re-do surgery; the overall mortality ratio was 10% including a case that was deceased on the tenth postoperative day following severe chest infection, and another case who had a massive acute non-haemorrhagic brain infarction after initial good recovery following surgery.
Belkhair and Pickett  suggested that using a single-burr hole craniostomy technique is as good as using two burr holes in evacuating CSDH, and the former was not associated with a higher recurrence rate compared to the latter.
Similarly, Han and colleagues  noted a higher recurrence rate in patients managed by two-burr hole craniostomy surgery in comparison to a single-burr hole craniostomy (6.82% and 1.89%, respectively); however, the number of burr holes as a risk factor of CSDH recurrence was not statistically significantly associated with postoperative recurrence rate (p > 0.05).
However, Taussky and colleagues  reported that single burr hole drainage was associated with a statistically significant higher rate of recurrence, a longer mean hospitalization period, and a higher rate of wound infection.
A theoretical explanation for higher recurrence rate of one-burr craniostomy suggested that the residual hematoma fluid contains large concentrations of fibrinolytic factors, inflammatory mediators, and vasoactive cytokines, and the complete evacuation of the CSDH, theoretically more achieved through the flush out of the subdural collection via two burr holes seems to be directly related to the success of surgical procedure .
Yamamoto and colleagues  demonstrated that drainage and irrigation through one burr hole is usually adequate to evacuate the hematoma even in multiple cavities concluding that multiplicity in CSDH mostly does not imply multiple closed cavities and that these cavities were in fact continuous with relatively wide routes of connections.
A single-burr hole craniostomy is hence less invasive method with a shorter operative time in contrast to a two-burr hole craniostomy surgery; however, it is often less efficient in cases of septated or acute (thick) subdural hematoma disallowing adequate evacuation.