Abstract
Intracranial Arachnoid Cysts (AC) are thought to be congenital occurring in young patient and diagnosed incidentally in almost cases, which explain the conservative treatment reserved to the majority of cases; at the opposite the Chronic Subdural Hematomas (CSDH) are chronic, acquired and commonly occurred in the elderly patients, hence, requiring surgical treatment.
We report a case of 8-years-old boy with left temporal fossa AC associated to a bilateral CSDH, presenting with a 3-months headache history along with mild head injury. Imaging studies revealed bilateral hygroma with AC on Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) of the brain. The young patient underwent left pterional craniotomy with drainage of the subdural collection which consisted on xantochromic content consisting with CSDH, under the operating microscope, marsupialization of the AC and partial resection of its membrane and fenestration in the basal cisterns. The outcome was favorable. This case pinpoints the importance of considering keeping patients harboring AC even asymptomatic, under close surveillance, which can help preventing certain complications like CSDH.
Keywords
arachnoid cysts, chronic subdural hematoma, mild head trauma
Introduction
The widespread use of CT and MRI notably in the context of mild head trauma has significantly increased the incidence of AC. Their prevalence is estimated at 0.7% to 1.7% of the population [1,2]. AC are thought to be congenital and often encountered incidentally after mild head trauma imaging. They are commonly observed in the middle fossa, mainly on the left side [3,4].
Their clinical presentation depends on their size and location. Small cysts are usually asymptomatic, requiring observation and follow up. However, larger cysts may have a mass effect on neurovascular structures, leading to neurological disturbance. Headaches are the most common symptom which can be accompanied by other symptoms such as dizziness, nausea, vomiting, worsening of mood, mental status changes, ataxia, and seizures
Majority of studies have suggested that AC is a risk factor for CSDH. However, this presentation is rare and their pathogenesis remains hypothetic [5,4]. The most frequently used methods for treating AC are microsurgical fenestration via craniotomy, neuroendoscopic fenestration and cyst peritoneal shunting [6,7]. CSDH is more commonly encountered in the elderly population. Head trauma has been recognized as an important factor in its development [8,9]. We report a patient with bilateral CSDH harboring an AC. Both conditions require surgery if symptomatic to relieve intracranial hypertension.
Case description
An 8-years-old boy was referred to our outpatient department complaining of a severe and progressive headache for 3-months, accompanied by nausea, vomiting, agitation, and drowsiness. There was a history of mild head trauma with unremarkable brain CT (except AC). He was conscious and oriented, with no neurological deficit but the fundus found bilateral papillary edema stage I. The patient was kept under observation and antalgic treatment before undergoing further examination.
The second brain CT one month after the head trauma showed bilateral subdural crescent-shaped collections which were taken for hygroma with left middle fossa AC grade II. Brain MRI one month after, showed a decrease in the size of the hygroma and persistence of the AC (Figure 1). Despite this, there was no relief of headaches and worsening at the fundus which found bilateral papillary edema stage II with ongoing optic atrophy. At admission, the patient was conscience, 15/15 GCS, with left VI cranial nerve palsy.
The surgery was indicated, and then we decided to proceed with left pterional craniotomy as this approach is a workhorse in neurosurgery, allowing at the same time access to the subdural collection and the AC. Upon incision of the dura, a “xantochromic” fluid, consistent with CSDH, was drained related to the subdural collection. The external arachnoid wall was pulled away and the AC was opened and its membrane partially resected, we proceeded to fenestration of the Sylvius fissure and ipsilateral basal cisterns and opto-chiasmatic cistern to connect the AC to them.
Figure 1. One week post head trauma axial and frontal CT scan (A,B) show left temporal AC and no evidence of CSDH. One month post head trauma axial CT scan(C) shows bilateral subdural collection. Axial T1W MRI (D,G), FLAIR MRI (E) T2W MRI (F), sagittal and coronal T2W MRI (H,I) images of an AC (red stars) with bilateral subdural collection (red arrows)
No complications were encountered during the operation. In the immediate postoperative period, the patient was headache free, and neurologically intact even the VI cranial nerve palsy disappeared. Histopathological examination of the cyst wall showed connective tissue lined by meningothelial cells, which was characteristic of AC (Figure 2). Brain CT fellow up showed no evidence of subdural collection and maintaining of AC (Figures 3 and 4).
Figure 2. The histopathological examination shows a cyst wall, which is composed of connective tissue lined by meningothelial cells, diagnostic of AC
Figure 3. Postoperative axial CT scann shows the bilateral removal of the subdural hematoma
Results and discussion
With the advent and accessibility of neuroimaging, there has been an increased incidence of incidental asymptomatic AC. They most frequently occur in the middle fossa, followed by the posterior fossa, convexity, and suprasellar region. Although these lesions are considered congenital, and thought to form due to derangement during arachnoid development, resulting in splitting of the arachnoid membrane with a space filled with CSF, mainly a mesenchymal condensation defect, but the exact pathogenesis is still unclear [10]. The associated subdural hematoma following head trauma are well documented, although the mechanism and exact incidence in the AC are not clearly understood [11,13].
Studies on middle cranial fossa AC evaluate the annual risk for hemorrhage below 0.1%. In a recent study by Wester, the incidence of chronic subdural or intracystic hematomas was reported as 4.6% of all patients with intracranial AC [13,5]. Two mechanisms leading to formation of subdural hemorrhage are suggested. First, the bleeding episode of cyst membrane closely attached to the convexity dura. Second, the disrupt of the bridging veins crossing the parietal cyst membrane [5]. A middle cranial fossa AC is now recognized as one of the causes of CSDH after trauma brain injury, especially in young people. Parsch suggests an approximately 5 times greater prevalence of AC of the middle fossa in patients with CSDH than in the general population [14].
The post-traumatic hemorrhagic complication of a temporal fossa AC is ipsilateral to the cyst. The occurrence of bleeding in the contralateral side as in our cases could be explained by the sudden collapse of the AC causing a sudden shift of the brain, which, along with the force of the trauma, can lead to stretching, and tearing of bridging veins [14,3]. Our patient is incidentally diagnosed for AC associated with bilateral CSDH related to recent history of head trauma. Literature suggests that young age, male gender of patients, middle cranial fossa location, larger cyst size and history of head injury seem to be at the greatest risk of complicated CSDH. Like our patient who harboring all the above criteria [15].
Patients with AC and their families should be aware of the possibility of such complications and advise care to avoid head trauma. The optimal treatment strategy is unanimous. Burr hole and drainage of the hematoma alone, craniotomy with drainage of the clot and excision/fenestration of the cyst. We have opted for the craniotomy in our case on the side of AC and the VI palsy which was left, however some studies suggest that corticosteroids might be beneficial in the treatment of CSDH [2,3,14].
Conclusion
The standard management of AC is conservative as are in majority incidentally detected and asymptomatic. Nevertheless, a minority part of them is symptomatic and life-threatening. Subdural hematoma following head trauma may result from inadequate intracranial cushioning provided by the incompliant AC, which makes bridging veins prone to tear. These rare complications with intracranial AC may increase the intracranial pressure and should be improved only by surgery. Drainage of the hematoma and by the same occasion marsupialization and fenestration of the AC in one side can drain spontaneously the contralateral one.
Conflicts of interest
I declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Financial support and sponsoring
None
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