Spontaneous rupture of an arachnoid cyst in an adult: illustrative case

Abstract

BACKGROUND

Arachnoid cysts are common intracranial mass lesions frequently discovered as incidental findings on radiographic imaging. It is routine practice to monitor these lesions as a large majority remain stable. Although traumatic cyst rupture is a known risk, it is rare for patients to present with spontaneous rupture.

OBSERVATIONS

The authors report the case of a 32-year-old patient who required emergent neurosurgical intervention for spontaneous rupture of a left hemispheric arachnoid cyst.

LESSONS

Patients with ruptured arachnoid cysts can present with vague, nonspecific symptoms that may delay diagnosis. If not diagnosed and treated promptly, arachnoid cyst rupture can progress to a neurosurgical emergency as the subdural collection may cause extensive mass effect and even cerebral herniation.

Intracranial arachnoid cysts are relatively common lesions characterized as intra-arachnoidal fluid-filled cysts, which often present as incidental findings on imaging obtained for unrelated reasons.¹ Most remain stable without ever causing clinical symptoms during the person’s lifetime. However, according to a large study by Al-Holou and colleagues,¹ approximately 5% of patients with intracranial arachnoid cysts are symptomatic, and sellar and suprasellar cysts are more likely to be symptomatic than those in other locations. Headaches are the most common presentation for symptomatic patients, although arachnoid cysts may also cause hydrocephalus, neuropathies, seizures, cognitive complaints, and other focal neurological deficits.^1,2 Rarely, arachnoid cysts can present as a neurosurgical emergency due to cyst rupture with subsequent intracystic hemorrhage or subdural hematoma causing mass effect or a rapid rise in intracranial pressure.^1,3 Few documented reports of spontaneous arachnoid cyst hemorrhages exist as this predominantly occurs following head trauma.^1,4 In this report, we describe a patient who presented with vague signs and symptoms initially attributed to a presumed viral infection. The patient’s symptoms progressively evolved into a neurosurgical emergency, with imaging revealing an arachnoid cyst that had spontaneously hemorrhaged, causing significant mass effect. The patient required emergent surgical intervention for evacuation of the hematoma causing uncal herniation and concurrent fenestration of the cyst.

Illustrative Case

A 32-year-old male with no initially known significant past medical history first presented to the emergency department with 3 days of generalized headache, sore throat, nausea, and self-reported fever. Influenza A test was positive, and he was discharged with a plan for supportive therapy. He presented to another emergency department 3 days later with ongoing headache and nausea with subtle lethargy, which was thought to be related to a viral infection, and he was discharged home again with a plan for supportive management. After 3 more days, he presented again to the initial emergency department with worsening headache and significant lethargy, now minimally responsive in bed. On initial examination at this presentation, the patient had a Glasgow Coma Scale (GCS) score of 9 with eyes remaining shut, was able to say his name, and was localizing in his upper extremities and withdrawing in his lower extremities, more briskly on his left side than his right side. At this point, his pupils were both 3 mm in diameter and reactive, although somewhat sluggish on the left.

Emergent computed tomography (CT)/CT angiography was performed (Fig. 1) demonstrating a mixed-density loculated extra-axial collection extending along the left cerebral convexity and into the left middle cranial fossa with a maximal length of 5 cm and maximal width of 2 cm with smooth remodeling of the superjacent frontal and temporal calvaria. This lesion was causing a 9-mm midline shift to the right with effacement of the left lateral ventricle, entrapment of the right lateral ventricle, and uncal herniation. Differential diagnoses included hemorrhagic meningioma versus hemorrhagic intrinsic tumor, including a low-grade glioma versus a ruptured arachnoid cyst. After returning to the emergency department from the CT scanner, the patient’s exam was noted to have declined further, now with a GCS score of 6 with no verbal responses and withdrawing rather than localizing In his right upper extremity. Furthermore, he had developed anisocoria with his right pupil 3 mm in diameter and his left pupil 5–6 mm in diameter. Hypertonic saline, mannitol, and corticosteroids were administered, after which his left pupil returned to 3-mm diameter and his GCS score increased to 8. Given his worsening poor exam and large mass lesion with brain shift, he was taken for an emergent left-sided craniotomy.

FIG. 1.

Longitudinal patient imaging. Axial (upper) and coronal (lower) baseline MRI from 8 years prior to presentation as well as CT scans from various points in the patient’s clinical course.

Intraoperatively, an apparent intracystic hemorrhage of a large left middle fossa arachnoid cyst was identified (Fig. 2A). The intracystic hematoma was removed when possible, and the cyst membrane was fenestrated (Fig. 2B). The specimen was sent for permanent pathology, which ultimately was consistent with thickened leptomeninges with a histiocytic infiltrate and focally abundant neutrophils (Fig. 3). A subdural hematoma overlying the left frontoparietal convexity was seen to be contained within a thickened membrane, and it was also evacuated (Fig. 2A).

FIG. 2.

A: Intraoperative photograph after opening the dura with a left frontotemporal arachnoid cyst with leakage of intracystic hemorrhagic products (a), left frontoparietal subdural hemorrhage with thick surrounding membrane (b), and patient’s left temporal lobe (c). B: Intraoperative photograph after intracystic hemorrhage evacuation and cyst fenestration with evacuated cyst with fenestration indicated by suction tip (a); left frontoparietal subdural hemorrhage (b), which was evacuated Orientation: A (anterior), S (superior), P (posterior), I (inferior) shortly afterwards; and patient’s left temporal lobe (c).

FIG. 3.

Surgical specimen pathology. A: Immunostaining for SSTR2 demonstrating a thin lining of leptomeninges (arrows) attached to a thick membrane composed of granulation tissue. B: Hematoxylin and eosin (H&E) staining illustrating the presence of acute hemorrhagic products (arrow) as well as hemosiderin deposition (arrowhead) indicative of remote hemorrhage. C and D: H&E staining revealing granulation tissue with small foci of extramedullary erythropoiesis (arrow). Original magnification ×10 (A and C) and ×20 (B and D).

Immediate postoperative CT scanning (Fig. 1) showed a hypodense collection within the cavity of the evacuated and fenestrated cyst with small-volume hyperdense layering, an extra-axial hyperdense collection under the craniotomy flap, and persistent rightward midline shift. On short-interval surveillance CT scans, the hyperdensity within the cyst cavity was found to increase slightly and then redistribute. The collection under the craniotomy flap was found to be stable.

On postoperative day (POD) 1, the patient’s neurological exam remained guarded, with equal and reactive pupils, a GCS score of 8, not opening eyes, groaning, and localizing in upper extremities. No seizures were found on continuous bedside electroencephalography. His exam steadily improved and, by POD 2, he had a GCS score of 15, was following commands in all extremities, was oriented to self only, and had mild weakness in his left arm. A CT scan on POD 7 (Fig. 1) showed an improving midline shift with stable hyperdensities under the craniotomy flap and in the cyst cavity. Over the course of his hospitalization, the patient’s clinical exam continued to improve, and he was discharged home on POD 11 neurologically intact, aside from mild balance and cognitive deficits. A follow-up CT scan on POD 34 (Fig. 1) demonstrated near resolution of the previously noted hyperdense collections and midline shift. By the patient’s last follow-up visit, on POD 50, he had returned to work. He reported occasional left-sided paresthesias but was otherwise neurologically intact with full strength and no subjective cognitive changes.

Upon retrospective collection and review of external medical records after the patient’s surgery, it was found that the patient’s left-sided arachnoid cyst had been incidentally discovered 8 years prior at an unaffiliated outside hospital in the setting of workup for nasal sinus discomfort (Fig. 1).

Discussion

Observations

Arachnoid cysts are extra-axial, intra-arachnoid collections of cerebrospinal fluid (CSF) occurring anywhere along the cerebrospinal axis.^1,5 With an estimated prevalence of 1.4%, they are among the most frequently encountered intracranial mass lesions.¹ Many arachnoid cysts are congenital (primary) and thought to occur from failure of embryonic meninges to fuse during sylvian fissure development.^5,6 Less common are acquired (secondary) arachnoid cysts, which arise from splitting of the arachnoid membrane following trauma, surgery, or infection.^5,6 The process by which CSF accumulates in the cyst is uncertain, but hypothesized mechanisms include the unidirectional inflow of CSF (ball-and-valve mechanism) or the internal production of CSF-like fluid by cells lining the cyst wall.^3,7

The vast majority of arachnoid cysts are asymptomatic and discovered incidentally on radiographic imaging obtained for an unrelated reason—appearing as well-circumscribed, extra-axial simple cystic lesions. There is often evidence of chronicity, such as thinning of the superjacent calvaria and absent edema within the surrounding brain parenchyma despite substantial mass effect.⁷ On magnetic resonance imaging (MRI), arachnoid cysts demonstrate T2 hyperintensity that is isointense to CSF and completely suppressed on fluid-attenuated inversion recovery (FLAIR) sequences. Unlike dermoid or epidermoid cysts, they exhibit no restricted diffusion on diffusion-weighted imaging.⁷

While most arachnoid cysts are benign, indolent lesions that remain clinically asymptomatic for the entirety of a patient’s lifespan,^1,7 an estimated 5% become clinically apparent and present with signs and symptoms of increased intracranial pressure and mass effect such as headache, focal neurological deficits, and seizures.^1–3,8 Rarely, they can cause significant and urgent clinical problems, most notably cyst rupture, characterized by rupturing of blood vessels around the cyst wall or tearing of bridging veins within the cyst cavity.^1,9,10 The risk of rupture is estimated to be less than 0.04% per year and is typically provoked by physical exertion or after a traumatic insult.^1,2,4,6,8,11 Spontaneous cyst ruptures, as seen in this patient, are exceedingly rare. According to a recent report, only 57 cases of spontaneous rupture have been documented in the literature.¹⁰ The mechanism of action of spontaneous rupture is uncertain, but a proposed mechanism is that the influx of intravascular blood in the cranial space during Valsalva maneuvers pushes CSF into the arachnoid cyst from the subarachnoid space. Eventually, the cyst wall tears from the increasing intracystic pressure.^12–14 In this case, it is interesting to note the patient’s recent history of influenza, as coughing may have led to cyst rupture.

The most frequent radiological signs of a posttraumatic or spontaneous arachnoid cyst rupture are chronic subdural hematomas or subdural hygromas.¹⁰ Subacute subdural hematomas are also reported, albeit less frequently.¹⁰ Acute subdural hematomas seem to be exceptionally rare, with only 2 documented reports.^8,10,11

When ruptured arachnoid cysts present with active bleeding, they can constitute a neurosurgical emergency, especially when the patient is in the process of herniating. In these scenarios, as in our patient’s case, it is critical that the patient’s condition be diagnosed and acted upon in a rapid manner. Treatment involves hematoma evacuation to relieve mass effect and cyst fenestration to mitigate chances of re-rupture and re-accumulation. Surgery is typically curative, but recurrences have been reported. Additional complications after surgical decompression include hydrocephalus, subdural hematomas, intraparenchymal hemorrhage, cerebral edema, infection, and seizures.^1–5,15 Patients should be followed and monitored with imaging at appropriate time intervals. There is no consensus in the literature due to the rarity of surgery for ruptured cysts, but we follow the general principle of near-term and longer-term imaging and neurological assessment to monitor for any symptomatic cyst recurrence and/or growth. Similar to interval imaging previously described,¹⁶ our practice is to obtain an MRI at 1 month, 3 months, and 1 year postoperatively.

Patients with arachnoid cyst rupture commonly present with nonspecific symptoms, most frequently headache, nausea, and vomiting, which can cause delays in diagnosis.² For instance, although our patient’s clinical course resulted in a good outcome, he had multiple encounters with the medical system before his pathology was recognized and addressed. Our patient’s diagnosis may have been delayed in part due to unawareness of his history of an incidental arachnoid cyst. Although his cyst had been discovered 8 years prior, the patient was not able to communicate this to the treatment team on account of his obtunded state at the time of presentation. This highlights the value of integrated health record systems, as it is possible that, with more readily available medical records, his history of an arachnoid cyst may have been recognized earlier by providers, and he might have undergone imaging and subsequent treatment sooner. It also underscores the importance of effectively communicating diagnoses to patients and their families. It is possible that language presented a barrier, as the patient and his family were primarily Spanish-speaking. Studies have demonstrated that immigrant and nonnative English-speaking patients disproportionately experience inadequate diagnostic, prognostic, and treatment comprehension.¹⁷ This case exemplifies the critical need for physicians to ensure patient comprehension, especially in immigrant patients for whom English is not the primary language.

Lessons

Although arachnoid cysts are typically incidental phenomena, they can rarely rupture spontaneously and cause intracystic and subdural hemorrhage that may require prompt diagnosis and neurosurgical intervention. It is important to be mindful of this potentially significant, albeit rare, entity in differential diagnosis formulations.

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: Jones, Nanda, Stemmer-Rachamimov. Acquisition of data: Jones, Nanda, Stemmer-Rachamimov. Analysis and interpretation of data: Jones, Nanda, Stemmer-Rachamimov. Drafting of the article: Jones, Leavitt, Nanda, Stemmer-Rachamimov. Critically revising the article: Jones, Leavitt, Nanda, Dunn. Reviewed submitted version of the manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Jones.