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Introduction Arachnoid cysts in the brain usually have an indolent course unless complicated by headache, seizures, increasing head circumference, behavioral disturbances, ocular, motor, speech disorders,[1] and sudden cyst changes such as acute cyst expansion, sudden hemorrhage into the cyst, subdural hematoma, or subdural hygroma. Rupture of arachnoid cyst causing subdural hygroma is very rare, with few case reports.[2] We herein present a clinical case, radiology, and discussion of asymptomatic middle cranial fossa arachnoid cyst in a 15-year-old male child who presented with raised intracranial features following a trivial trauma. Case Report A 15-year-old male child presented with complaints of headache, visual blurring, and projectile vomiting for 20 days duration. The child had a history of trivial fall about 10 days prior to onset of headache, with no loss of consciousness. On examination, the child had bilateral florid papilledema and right lateral rectus palsy. There were no other focal deficits or signs of meningeal irritation.

, and projectile vomiting for 20 days duration. The child had a history of trivial fall about 10 days prior to onset of headache, with no loss of consciousness. On examination, the child had bilateral florid papilledema and right lateral rectus palsy. There were no other focal deficits or signs of meningeal irritation. Computed tomography (CT) scan of the brain showed a left middle fossa, Galassi type 3 arachnoid cyst, with bilateral subdural hygroma/hematoma (chronic), bilateral diffuse cerebral edema, and mass effect causing compression of both frontal horns [Figure 1]. Magnetic Resonance Imaging (MRI) of the brain showed bilateral collection in the subdural space, hypo on T1W [Figure 2] and hyper on T2W [Figure 3] images, matching with the intensities of Cerebrospinal Fluid (CSF) with widened Sylvian fissure on the left side and a compressed temporal lobe on the left side, suggestive of arachnoid cyst with subdural hygroma and mass effect. Figure 1 Computed tomography scan plain, axial section showing hypodense region compressing the temporal horn with bilateral subdural hygroma Figure 2 Magnetic resonance imaging brain T1W image showing subdural hypointensity in the temporal region and bilateral convexities compressing temporal and frontal lobes on the left side suggestive of arachnoid cyst with subdural hygroma and mass effect Figure 3 Magnetic resonance imaging brain T2W image showing subdural hyperintensity in the temporal region and bilateral convexities compressing temporal and frontal lobes on the left side suggestive of arachnoid cyst with subdural hygroma and mass effect

Figure 2 Magnetic resonance imaging brain T1W image showing subdural hypointensity in the temporal region and bilateral convexities compressing temporal and frontal lobes on the left side suggestive of arachnoid cyst with subdural hygroma and mass effect Figure 3 Magnetic resonance imaging brain T2W image showing subdural hyperintensity in the temporal region and bilateral convexities compressing temporal and frontal lobes on the left side suggestive of arachnoid cyst with subdural hygroma and mass effect Left pterional craniotomy, evacuation of hygroma, fenestration of cyst into suprasellar cistern, and marsupialisation of the cyst was performed. The patient developed pseudomeningocele, which was managed with lumbar CSF drainage for 5 days and was discharged without any deficits. The postoperative imaging showed resolution of the subdural hygroma with small extradural and subgaleal collection of the CSF [Figure 4]. Figure 4 The postoperative imaging showed resolution of subdural hygroma with small extradural and subgaleal collection of cerebrospinal fluid Discussion Arachnoid cysts are considered intra-arachnoidal in location and account for 1% of the intracranial mass lesions. They can develop anywhere in the cerebrospinal axis but have a predilection toward the middle cranial base. They are usually asymptomatic, but may present with raised intracranial pressure, focal neurologic deficits, or seizures. Being indolent and slowly growing, most of the arachnoid cysts can be managed conservatively, reserving surgical intervention for symptomatic lesions.

a predilection toward the middle cranial base. They are usually asymptomatic, but may present with raised intracranial pressure, focal neurologic deficits, or seizures. Being indolent and slowly growing, most of the arachnoid cysts can be managed conservatively, reserving surgical intervention for symptomatic lesions. Intra-cystic hemorrhage and subdural rupture of the veins running over the surface of the cyst are well described.[23] Subdural rupture of the arachnoid cyst per se,[4–6] either traumatic or spontaneous, is sparingly reported with about 21 cases documented in literature. Even a minor trauma can cause rupture of the cyst as seen in the present case, where the patient fell down while playing, without any loss of consciousness. The gradual seepage of the CSF from the cyst into the subdural space, probably through a “flap- valve” effect,[7] caused a gradual rise in the intracranial pressure. Ruptures are usually asymptomatic in areas other than the cysts in the middle cranial fossa.[8] The procedures described in the literature vary from subgaleal drainage to cystocisternal fenestration. However, immediate operative intervention was warranted in view of raised intracranial pressure and progressive neurologic deterioration. Source of Support: Nil. Conflict of Interest: None declared.