Case Description: A 15-year-old healthy boy with a recent history of head trauma experienced headache that gradually worsened over the course of 10 days. He underwent CT and MRI brain scans which revealed the presence of subdural haematoma caused by the rupture of a middle cranial fossa arachnoid cyst. This was accompanied by intracystic haemorrhage. The subdural haematoma was removed, while communication of the cyst with the basal cisterns was also performed. The postoperative course of the patient was uneventful.

Conclusions: The annual haemorrhage risk for the patients with middle cranial fossa cysts remains very low. However, when haemorrhage occurs, in most occasions it can be effectively managed only with haematoma evacuation.

Usually these cysts overlie the sylvian fissure in the middle cranial fossa^1,2. Subdural haematomas, hygromas and intracystic haemorrhage are infrequently encountered complications of AC⁴. We describe a case of a boy with a middle cranial fossa AC associated with intracystic haemorrhage and subdural haematoma as a result of a preceding head trauma.

A 15-year-old developmentally normal, healthy boy presented with a 10-day history of gradually worsening headache accompanied by constant nausea and intermittent vomiting. His recent history was remarkable for head injury occurred during an athletic event. Initially, he experienced mild headache that became more severe and resistant to mild analgesia and bed rest. His level of consciousness was normal without any visual disturbances although funduscopic examination revealed bilateral papilledema. Of note, the patient has not received any drug that could have implicated with hemorrhagic phenomena.

The CT scan of the brain demonstrated subacute subdural haematoma in the right frontotemporal region with intracerebral edema and midline shift. No other space-occupying lesions were identified (Figure 1).

Figure 1. Computed Tomography (CT) scan showing the presence of subdural haematoma in the right frontotemporal region (arrows)

The aforementioned findings were inconsistent with a mild head trauma. Therefore, a MRI examination was ordered which showed the presence of a cystic lesion in the right middle fossa on T1 and T2 weighted sequences with a hyper intense signal inside the cystic cavity on T1 sequence. Additionally, the presence of the subdural collection was confirmed (Figure 2).

Figure 2. Sagittal T1 post contrast Magnetic Resonance Imaging (MRI) scan (a) and T2 sequence MRI scan clearly demonstrating arachnoid cyst, subdural haematoma and intracystic hemorrhage (arrows)

During surgery the subdural haematoma was evacuated and the intracystic blood clots were removed. A wide communication of the cyst with the subarachnoid space was obtained via marsupialisation.

Postoperatively, the clinical symptoms totally resolved. At one year follow-up CT examination there was no evidence of subdural haematoma. Although the size of the cyst had remained unchanged, no mass effect was identified. Hemorrhagic signs were not present inside the cystic cavity. (Figure 3)

Figure 3. Postoperative axial CT scan with contrast enhancement at 1-year. The arachnoid cyst in the right temporal lobe is present with no evidence of intracranial hemorrhage and mass effect (arrow)

Arachnoid cysts are congenital fluid-filled compartments within cerebrospinal fluid (CSF) cisterns and major cerebral fissures, intimately bordered by the arachnoid membrane. The cysts are filled with clear, colourless fluid nearly identical to CSF ⁵. They have been originally described on autopsy reports from the early 19^th century⁶

True arachnoid cysts are congenital. They may develop when alterations of CSF flow during the early phase of subarachnoid space formation lead to rupture of the developing webbed arachnoid. An alternative theory involves splitting of the arachnoid membrane during delamination from the overlying dura. However, the exact mechanism remains speculative⁷.

The first description of an AC with intracystic bleeding or subdural haematoma was described in 1938⁸. The coexistence of an intracranial cyst with intracystic bleeding and subdural haematoma is quite rare. To our knowledge, less than such 40 cases have been confirmed¹.

Arachnoid cysts show a slight predilection for the male sex⁴. They can develop anywhere within the subarachnoid space, intimately related to the cisterns. In the general population, nearly half of cysts occur within the sylvian fissure. It is also known that the supratentorial cysts far outnumber the infratentorial ones⁹. Less common sites of appearance are the suprasellar region, the cerebellopontine angle, the cerebral convexity and the quadrigeminal plate¹⁰.

A majority of the arachnoid cysts are recognized during the first two decades of life. Their natural history and course are poorly understood. Most of them constitute dormant fluid compartments that remain silent for many years. In distinct cases they enlarge producing mass effect on brain structures⁵. Signs related to arachnoid cysts include cranial enlargement, seizures, hydrocephalus and mental retardation¹¹. In middle cranial fossa cysts, headache is the most frequent presenting symptom¹². In rare occasions they can resolve spontaneously¹³.

On Computed Tomography (CT) scan arachnoid cysts appear normally as extra-parenchymal hypo intense without any contrast-medium enhancement. In post traumatic cases however, the borders of isointense AC are not clearly demonstrated. In these patients, cyst location and relationship to adjacent structures is best visualized by T1 weighted sequences. Cyst fluid has normally low attenuation on T1 images and a high signal on T2 sequences which is nearly identical to CSF. However, previous intracystic haemorrhage may change the attenuation values in all image sequences¹⁴.

Intracystic haemorrhage and/or subdural haematoma as a complication of AC may occur spontaneously or after a minor head trauma. They may result from rupture of the intracystic or bridging vessels¹⁵. This could be presumably explained by the presence of unsupported veins that surround the cyst walls. Moreover, the fragile supporting stroma also predisposes to rupture even after a minor injury¹⁵. In some occasions, subsequent re-bleed or osmotic influx of fluid could explain the gradual increase in the subdural or intracystic fluid collection³.

Management decisions balance the imaging findings and the clinical symptoms. Many collections are asymptomatic and are managed conservatively with observation. However, symptomatic patients are candidates for surgery². Sizeable subdural collections with mass effect should be evacuated with application of usual neurosurgical techniques. The optimal cyst manipulation is still under debate. The two most commonly used surgical procedures are cyst peritoneal shunting and cyst fenestration¹⁶. Endoscopic membrane excision has also been used with good outcomes¹⁷. Whatever the choice of the surgical procedure, membranectomy and cyst communication to the basal cisterns must be accomplished¹⁹.

The broad use of CT and MRI has increased the frequency of diagnosed arachnoid cysts as well as the detection of their possible complications. The outcome is generally excellent. The indications for surgical intervention are not clearly defined. Further improvements in neuroendoscopic and surgical techniques are expected to perform a major role in the future.