eMedicine Specialties > Radiology > Brain/Spine

Arachnoid Cyst

Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, Consultant Radiologist and Honorary Professor, North Manchester General Hospital Pennine Acute NHS Trust, UK
Ian Turnbull, MB, ChB, MD, DMRD, FRCR, Lecturer, Department of Radiology, University of Manchester; Consulting Neuroradiologist, Hope Hospital, Salford, Manchester and North Manchester General Hospital, UK; Riyadh Al-Okaili, MBBS, Interventional/Therapeutic and Diagnostic Neuro-Radiologist, King Abdulaziz Medical City; Sumaira MacDonald, MBChB, PhD, MRCP, FRCR, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute; Khalid Mahmood, MBBS, FCPS, Locum Appointment Training Specialist Registrar, Department of Radiology - Paediatric, Royal Liverpool (Alder Hey) Children's Hospital

Updated: Sep 21, 2009

Introduction

Background

Arachnoid cysts are benign cysts that occur in the cerebrospinal axis in relation to the arachnoid membrane and that do not communicate with the ventricular system. They usually contain clear, colorless fluid that is most likely normal cerebrospinal fluid; rarely, they contain xanthochromic fluid. Most are developmental anomalies. A small number of arachnoid cysts are acquired, such as those occurring in association with neoplasms or those resulting from adhesions occurring in association with leptomeningitis, hemorrhage, or surgery. They constitute approximately 1% of intracranial masses; 50-60% occur in the middle cranial fossa. Cysts in the middle cranial fossa are found more frequently in males than in females; they occur predominantly on the left side. Most arise as developmental anomalies. A small number of arachnoid cysts are associated with neoplasms.

T2-weighted sagittal MRI image (see Image below for axial view) of the brain in a 28-year-old woman with an incidental finding of a superior cerebellar cistern arachnoid cyst (arrow).

T2-weighted axial MRI image (see Image above for sagittal view) of the brain in a 28-year-old woman with an incidental finding of a superior cerebellar cistern arachnoid cyst (arrow).

Arachnoid cysts also occur within the spinal canal; in such cases, arachnoid cysts or arachnoid diverticula may be located subdurally or in the epidural space, respectively. Spinal arachnoid cysts are commonly located dorsal to the cord in the thoracic region. A cyst in this location is usually secondary to a congenital or acquired defect and is situated in an extradural location. Intradural spinal arachnoid cysts are secondary to a congenital deficiency within the arachnoidal trabecula, especially in the septum posticum, or are the result of adhesions resulting from previous infection or trauma. Microscopic examination shows that their walls are formed from a splitting of the arachnoid membrane, with an inner and outer leaflet surrounding the cyst cavity.¹

Arachnoid cysts often are an incidental finding on imaging. Usually, arachnoid cysts are asymptomatic; this is true even of cysts that are quite large. The most commonly associated clinical features are headache, calvarial bulging, and seizures; focal neurologic signs occur less frequently. Controversy surrounds the treatment of arachnoid cysts. Some clinicians advocate treating only patients with symptomatic cysts, whereas others believe that even asymptomatic cysts should be decompressed to avoid future complications. The most effective surgical treatment appears to be excision of the outer cyst membrane and cystoperitoneal shunting.

Recent studies

Algin et al measured the sensitivity and specificity of intraventricular arachnoid cysts (IV-ACs) and their communication with CSF spaces using phase-contrast cine magnetic resonance imaging (PC-MRI) and compared the PC-MRI findings with those on MR cisternography (MRC) in 21 patients. The sensitivity and specificity of PC-MRI in identifying communications between IV-ACs and the CSF were 100% and 54%, respectively. In 7 IV-ACs, there was no communication detected on PC-MRI, and in 14 cases, a pulsatile CSF flow was seen into the IV-ACs. All the IV-ACs that were determined as noncommunicating on PC-MRI were corroborated on MRC. Six cases in which a communication was shown on PC-MRI were not corroborated on MRC. MRC revealed a total of 8 communicating and 13 noncommunicating IV-ACs in the 21 patients.²

Spacca et al studied 40 patients retrospectively (cases from 2001-2007) who had undergone endoscopic fenestration for middle fossa arachnoid cysts to identify indications for treatment and clinical and neuroradiologic results. In 29 patients, the cyst was reduced or it disappeared completely, and there were no deaths or significant morbidity associated with the endoscopic fenestration procedure. In 4 patients, further surgical treatment was required, and posttraumatic intracystic bleeding occurred in 4 patients after surgery. From their experience, the authors concluded that endoscopic fenestration was as effective and as safe as microsurgical fenestration and cyst shunting while being less invasive. They note, however, that the risk of hemorrhage may not be reduced.³

Pathophysiology

Cystic lesions localized within the arachnoid membrane may be classified according to the location along the neural axis or by the histologic composition of the cyst wall, which is either arachnoid connective tissue or glioependymal tissue. Distribution of these 2 types of cysts differs along the neural axis. The cysts located along the cerebral convexity and in the spinal cord are mostly arachnoid, whereas cysts found in the supracollicular or retrocerebellar region may be either arachnoid or glioependymal cysts.

Microscopic examination of arachnoid cysts shows that the walls are formed from a splitting of the arachnoid membrane, with an inner and outer leaflet surrounding the cyst cavity. The cyst wall consists of fibrous connective tissue slightly denser than normal arachnoid tissue; occasionally, hyaline changes occur. No epithelial lining is present. The outer wall of the cyst adheres loosely to the dura. The cyst wall is devoid of blood vessels; inflammation or hemorrhage seldom occurs.

Arachnoid cysts usually occur in association with normal arachnoid cisterns; such cysts are congenital, arising from arachnoid clefts and arachnoid duplications. Glioependymal cysts are rare; only a few instances of interhemispheric glioependymal cysts are known. Glioependymal cysts may be associated with agenesis of the corpus callosum, heterotopia, and other dysplasias.

Arachnoid cyst expansion most likely occurs when intracranial pulsation pushes CSF through defects (which behave like valves); CSF then becomes entrapped in arachnoid locations. Less likely, expansion occurs when the cyst wall excretes fluid, perhaps along an osmotic gradient. The cysts may be unilocular or loculated by septations. The wall of the cyst is usually smooth. Most cysts are filled with clear, colorless fluid of low protein content that is comparable to that of CSF. In a few cysts, the protein content is elevated.

In gross appearance, glioependymal cysts are usually indistinguishable from arachnoid cysts; however, their microscopic appearances vary. Glioependymal cysts have epithelial lining and may bear cilia. When the epithelial lining is lacking, glial tissue is seen to line the lesion. Glioependymal cysts are believed to derive from displaced neuroectodermal tissue. Histologic classification is only of systematic interest and has little bearing on prognosis.

Acquired arachnoid cysts may develop following surgery, trauma,⁴ subarachnoid hemorrhage, or neonatal infections; they occasionally occur in association with extra-axial neoplasm. Arachnoid cysts associated with tumors develop as a consequence of CSF loculation surrounded by arachnoid scarring, with expansion resulting from osmotic filtration or via a ball-valve mechanism. These acquired arachnoid cysts have been described variably as acquired, secondary, or leptomeningeal cysts. The reason arachnoid cysts grow and come to occupy space is far from clear. No inner lining is present through which active transport can take place. Neurosurgeons have observed ostia with pulsating fluid in exposed cysts, suggesting a hydrodynamic flap-valve or ball-valve mechanism. Cine MRI has shown abnormal fluid flow in intradural spinal arachnoid cysts presenting with cord compression.

A common location is in the floor of the middle cranial fossa, particularly anteriorly and parasagittally in the interhemispheric fissure. Most cysts are unilateral, smoothly rounded, and adhere loosely to the dura. Arachnoid cysts may indent deeply into the hemisphere or invaginate into major fissures, displacing and flattening the underlying cortex. Compression severe enough to cause tissue necrosis is exceptional. Other locations of arachnoid cysts include the suprasellar/chiasmatic site (cysts in this location may cause endocrinopathy); the cerebellopontine angle (11%); the quadrigeminal plate cistern (10%); in relationship with the vermis (9%); and in the prepontine/interpeduncular cistern (3%). Patients with spinal arachnoid cysts may become symptomatic because of local cord displacement/cord compression. Typically, this occurs at the midthoracic level; less frequently, it occurs at the lumbosacral or sacral level.

In juveniles, epidural arachnoid cysts often are associated with kyphoscoliosis. Spinal arachnoid cysts form elongated membranous sacs of CSF dorsal to the cord. Some cysts have no connection to the dura, whereas others communicate with the subarachnoid space via a thin stalk penetrating the dura. Arachnoid cysts are associated with myelodysplasia in cases of spinal dysraphism.

Presentation

Demographics

• Arachnoid cysts constitute 1% of intracranial masses; 50-60% occur in the middle cranial fossa.
• Morbidity and mortality depend on the location of the arachnoid cyst and on the occurrence of complications, such as acute mass effect by intracystic hemorrhage or the development of a subdural hygroma/hematoma.^5,6 The exact incidence of mortality and morbidity from an arachnoid cyst is not known. Arachnoid cysts may cause occlusive hydrocephalus by compression of the fourth ventricle.^7,8
• The male-to-female ratio is 4:1.
• Patients of any age may present with a symptomatic arachnoid cyst.^9,10

Anderson and Landing¹⁵ and Aicardi and Bauman⁹ described the clinicopathologic features of supratentorial cysts in infancy. Neither a history of antecedent trauma nor the clinical features of preceding cranial trauma was noted in the infants. The infants had a tense fontanelle and widened cranial sutures. Craniomegaly was present either diffusely or with localized protrusion, with transillumination and thinning of the calvarium, as noted on skull radiographs.

In symptomatic patients, clinical features depend on the location of the arachnoid cyst. Cysts of the middle cranial fossa (50%) may compress the tip of the temporal lobe, displacing it in the occipital direction. Cysts of the middle cranial fossa have been linked to ipsilateral chronic subdural hematomas. Rarely, such cysts may communicate with the subdural space, forming a slitlike extension over the hemispheric surface.³

Arachnoid cysts are found in several syndromes, but data are not sufficient to indicate whether the association is typical or fortuitous. Arachnoid cysts may be associated with Cockayne syndrome and Menkes syndrome. Ependymal cysts are common in oral-facial-digital syndromes. Patients with spinal arachnoid cysts may develop symptoms associated with local cord displacement or cord compression. Typically, spinal arachnoid cysts occur at the midthoracic level; less frequently, they occur at the lumbosacral or sacral level. Epidural arachnoid cysts often are associated with kyphoscoliosis in juveniles. Arachnoid cysts also are associated with myelodysplasia in cases of spinal dysraphic lesions. Pain produced by intraspinal arachnoid cysts typically is aggravated by the Valsalva maneuver, which increases pressure within the cyst.

Spinal arachnoid cysts are generally misdiagnosed, because symptoms are often nonspecific. Often, the cysts are an incidental finding on MRI. Asymptomatic cysts do not require intervention, regardless of their size. Cysts that cause symptoms from cord compression are best evaluated with MRI; they should be surgically excised, if possible.^16,17,18,2

Preferred Examination

MRI is the diagnostic procedure of choice because of its ability to demonstrate the exact location, extent, and relationship of the arachnoid cyst to adjacent brain or spinal cord. Myelography and CT myelography remain of diagnostic value, especially for cases that are not definitive on MRI.

Plain radiographic findings are nonspecific and have little to offer in the diagnosis of arachnoid cysts, although changes in skull contour may be detected on skull radiographs performed for other indications, such as trauma.

Cranial ultrasonography is an important diagnostic tool during the first year of life. Although symptomatic arachnoid cysts are comparatively rare in infants, ultrasound is useful as a noninvasive imaging technique with high yield in the detection and characterization of cystic masses.

Although angiography may show associated anomalies of venous drainage and the relationship of the lesion to normal vasculature, which may be useful for surgical planning, in practice, angiography is rarely performed, because CT angiography or magnetic resonance angiography provides the same information noninvasively.

Every effort must be made to reliably detect arachnoid cysts, because most arachnoid cysts are an incidental finding and most patients are asymptomatic. Arachnoid cysts must be differentiated from the more serious cystic intracranial and intraspinal tumors. In cases involving larger arachnoid cysts, consideration should be given to the use of serial scans, because such cysts may enlarge over time; patients with such cysts may become candidates for surgery.

Limitations of Techniques

Skull radiographic findings cannot be relied upon because the signs are nonspecific. Arachnoid cysts may be confused with several intracranial cysts of various etiologies (see Differentials, below). The confusion is much more likely to occur with CT. CT attenuation values and signal intensities of arachnoid cysts parallel those of CSF, and difficulties may be encountered in cases of hemorrhagic cysts.

The most important differentiation to make is between arachnoid cysts and epidermoid cysts; MRI diffusion-weighted images (DWIs) make differentiating the 2 masses easier. Some arachnoid cysts contain proteinaceous fluid or blood; in such cases, signal loss on DWIs may not be marked, which may pose diagnostic problems. Also, tissue contrast with fluid-attenuated inversion recovery (FLAIR) imaging is similar to that with a T2-weighted image, but FLAIR shows no signal arising from the CSF. Thus, unlike with epidermoid cysts, arachnoid cysts containing CSF demonstrate a suppressed (low) signal on FLAIR.

Differential Diagnoses

Epidermoid, Brain
Hydatid cyst

Other Problems to Be Considered

Epidermoid cyst
Dermoid cyst
Supracollicular cysts — All causes of hydrocephalus
Cerebellopontine angle cysts — Acoustic neuroma and epidermoid cysts
Intracerebral cysts — Cerebral abscess, cystic tumors, and parasitic cysts
Basal midline cysts — Midline cysts associated with agenesis of corpus callosum and other causes of hydrocephalus
Posterior fossa cysts — Dorsal cyst associated with holoprosencephaly, Dandy-Walker cyst, and vein of Galen aneurysm

Deep invagination of an arachnoid cyst into the cerebral hemisphere may simulate porencephaly to such an extent that it has been termed pseudoporencephaly. However, the inferior aspect of the arachnoid cyst shows a displaced but otherwise normal cerebral cortex, whereas in porencephaly, the surrounding cortex and white matter are abnormal.

Chronic subdural hygromas usually are located subdurally rather than in the subarachnoid space; they are often bilateral and are flat or lentiform in profile. Hygromas compress but do not invaginate sulci or fissures.

Intraspinal cysts

• Cystic loculations in adhesive arachnoiditis (often multiple; other features of arachnoiditis may be evident)
• Epidural acquired arachnoid cysts secondary to penetrating trauma or surgery
• Meningoceles (most common in the lumbosacral region; readily identified in association with spina bifida)
• Cysts of dorsal nerve root ganglia (observed in 8-24% of autopsies, although not in children)
• Extradural ganglion cysts (presumably arising from bursae of the vertebral joints; seen in elderly patients)
• Tarlov cysts (perineural cysts of sacral or coccygeal nerve roots arising between the layers of connective tissue covering the nerve roots; communication between the cyst and subarachnoid space may be present)

Radiography

Findings

Intracranial

• Forward bowing of the anterior cranial wall of the middle cranial fossa and elevation of the sphenoidal ridge have been reported findings on skull radiographs of patients with arachnoid cysts of the middle cranial fossa.
• In infants, craniomegaly associated with widening of the fontanelle and thinning of the calvarium may be observed.

Spinal

• The spinal canal may be widened.
• Erosion of the pedicles may occur.

Accuracy

• Plain radiographs have low sensitivity in the diagnosis of arachnoid cysts and contribute little to the diagnosis.

Imaging pearls

• Forward bowing of the anterior cranial wall of the middle cranial fossa and elevation of the sphenoidal ridge are difficult to assess; occasionally, patients with these features may be difficult to differentiate from normal patients. Changes seen in other conditions, such as neurofibromatosis type I, may mimic these changes.
• In infants, craniomegaly associated with widening of the fontanelle and thinning of the calvarium may be a normal variant and may be associated with other intracranial pathology.
• In cases involving spinal canal widening and erosion of the pedicles, the differential diagnosis is wide and includes spinal cord tumors.

Computed Tomography

Unenhanced CT scan of the head in a 26-year-old man with a history of seizures since childhood (same patient as in Image below). The scan shows a large left frontoparietal cyst with a mass effect. The cyst was resected, and histologic analysis confirmed an arachnoid cyst.

Unenhanced CT scan of the head in a 26-year-old man with a history of seizures since childhood (same patient as in Image above). The scan shows a large left frontoparietal cyst with a mass effect. The cyst was resected, and histologic analysis confirmed an arachnoid cyst.

Findings

Intracranial

• Typically, in cases of arachnoid cysts, the subarachnoid space is compressed by a cystic structure that may be unilocular or septate. The size of such structures varies. The septa may not always be visible (see Images above and Images 3-4 in Multimedia Section).
• The subjacent brain shows minimal mass effect.
• On CT scans, arachnoid cysts are characterized by sharp, nonenhancing borders; they are isodense to CSF.
• On a bone window, remodeling of the skull may be evident.
• Arachnoid cysts seldom calcify.
• On CT cisternography, arachnoid cysts may be seen to have a smooth outer surface, in contradistinction to epidermoid cysts, which typically have an irregular outer surface that is likened to the surface of cauliflower. With respect to cyst filling, CT cisternography yields mixed results. Some cysts fill with contrast immediately; with others, either filling is delayed or no filling occurs.
• Noncommunicating and slow-filling cysts are regarded as true arachnoid cysts, whereas communicating cysts are regarded as diverticula of the subarachnoid space.
• It has been proposed that noncommunicating cysts expand either as the result of a ball-valve mechanism or because of fluid secretion by the cyst wall, perhaps along an osmotic gradient.

Spinal

• On CT scanning, spinal arachnoid cysts may not be sufficiently characterized to preclude the need for further imaging. CT scanning of the spine is useful in establishing the differential diagnosis of nondiscogenic radiculopathy; it addition, it demonstrates bone detail well.

Imaging pearls

• Intracranial arachnoid cysts may be an incidental finding on CT scans.
• In asymptomatic patients, no further investigation is required.
• CT cisternography yields mixed results, with some cysts filling with contrast and others showing no filling.
• Although CT scanning of spinal arachnoid cysts may not be sufficiently characterized to preclude further imaging, CT scanning of the spine is useful in establishing the differential diagnosis of nondiscogenic radiculopathy. 
• It demonstrates bone detail well.
• CT myelography remains of diagnostic value, especially in cases in which a diagnosis of arachnoid cysts is not made with MRI.
• There is a wide differential diagnosis for both intracranial and intraspinal cystic lesions, and arachnoid cysts have several mimics. In particular, with hemorrhagic arachnoid cysts, difficulties are encountered when the cyst contents are no longer isodense to CSF.

Magnetic Resonance Imaging

T2-weighted sagittal MRI image (see Image below for axial view) of the brain in a 28-year-old woman with an incidental finding of a superior cerebellar cistern arachnoid cyst (arrow).

T2-weighted axial MRI image (see Image above for sagittal view) of the brain in a 28-year-old woman with an incidental finding of a superior cerebellar cistern arachnoid cyst (arrow).

Axial T2-weighted MRI image through the midbrain, showing a right middle cranial fossa homogeneous lesion (same lesion as in Image below) with CSF signal intensity and no perceptible wall or internal complexity. There is associated remodeling of the adjacent sphenoid bone and brain displacement. These imaging features are typical of an arachnoid cyst.

Axial T2-weighted MRI image through the body of the lateral ventricles, showing superior extension of a right middle cranial fossa lesion (same lesion as in Image above). The lesion is homogeneous, with no perceptible wall, no internal complexity, and CSF signal intensity. There is associated remodeling of the adjacent calvarium and brain displacement. These imaging features are typical of an arachnoid cyst.

Prenatal coronal T1-weighted MRI images through the middle cranial fossa, showing a left temporal fossa homogeneous lesion (postnatal images of same patient shown in Images below) with CSF signal intensity and no perceptible wall or internal complexity. There is associated displacement of adjacent brain. These imaging features are typical of an arachnoid cyst.

Postnatal coronal T2-weighted MRI images through the middle cranial fossa, showing a left temporal fossa homogeneous lesion (prenatal images of same patient shown in Images above and below) with CSF signal intensity and no perceptible wall or internal complexity. There is associated remodeling of adjacent calvarium, brain displacement, and a midline shift. These imaging features are typical of an arachnoid cyst.

Postnatal coronal T1-weighted MRI images through the middle cranial fossa, showing a left temporal fossa homogeneous lesion (prenatal images of same patient shown in Image above) with CSF signal intensity and no perceptible wall or internal complexity. There is associated remodeling of adjacent calvarium, brain displacement, and a midline shift. These imaging features are typical of an arachnoid cyst.

Findings

Intracranial

• On MRI, arachnoid cysts appear as well-defined nonenhancing intracranial masses that are isointense to CSF (see Images above and Images 1-2, 5-11 in Multimedia Section).
• Diagnostic confusion occasionally arises between arachnoid cysts and epidermoid cysts. The 2 masses may have similar characteristics on T1-weighted and T2-weighted images, and neither shows enhancement with gadolinium. However, arachnoid cysts follow CSF signals on all sequences—in particular, on the FLAIR sequence—in contradistinction to epidermoid cysts. DWIs allow easier differentiation of the 2 masses.
• Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans.
  • NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.
• As a result of the CSF contents of arachnoid cysts, the signal intensity on DWI is low.
• Epidermoid cysts tend to have a high signal on DWI.
• Some arachnoid cysts contain proteinaceous fluid or blood. In such cases, signal loss on DWI may not be marked; this may pose diagnostic problems when using DWI.
• FLAIR imaging demonstrates tissue contrast similar to that of T2-weighted images, but FLAIR shows no signal arising from the CSF. Therefore, FLAIR demonstrates a suppressed (low) signal in arachnoid cysts that contain CSF; in epidermoid cysts, that signal is typically higher.
• A large cisterna magna (mega cisterna magna) occasionally may be confused with an arachnoid cyst. Mega cisterna magna may represent a normal variant (intact cerebellum and vermis), but it may be associated with Dandy-Walker syndrome, either full blown or a variant in which the vermis is either completely or partially absent. Both mega cisterna magna and arachnoid cysts show CSF characteristics on T1-weighted, T2-weighted, DWI, and FLAIR sequences. However, whereas an arachnoid cyst may demonstrate mass effect with an en bloc displacement of the cerebellum and vermis, normal-variant mega cisterna magna demonstrates no mass effect, and the cerebellum and vermis remain intact.

Spinal

• MRI of spinal arachnoid cysts demonstrates an oval, sharply demarcated extramedullary mass that may cause local displacement, spinal cord compression, or both.
• The cyst is usually hyperintense to CSF on T2-weighted sequences because of the relative lack of CSF pulsation artifacts.^19,20,21,22

Accuracy

• MRI is the diagnostic procedure of choice in the detection of both intracranial and intraspinal arachnoid cysts because of its potential to demonstrate the exact location of the cysts, their extent, and their relationship to the brain and spinal cord.

Imaging pearls

• The most important mimic of an arachnoid cyst is an epidermoid cyst. 
• Arachnoid cysts may usually be distinguished from epidermoid cysts using DWIs.
  • However, some arachnoid cysts may contain proteinaceous fluid or blood, and signal loss on DWI may not be marked; this may pose diagnostic problems when using DWI. In such cases, a CT myelogram or cisternogram may be used. Occasionally, a large cisterna magna is difficult to differentiate from an arachnoid cyst because the 2 masses have similar signal characteristics on T1-weighted, T2-weighted, DWI, and FLAIR sequences.

Ultrasonography

Findings

Imaging pearls

• Cranial ultrasonography is an important diagnostic tool during the first year of life; it is limited by the closure of the anterior fontanelle, which normally occurs in full-term infants 9-18 months of age.
• In infants, arachnoid cysts are rarely symptomatic.
• Ultrasound is a noninvasive imaging modality that has a high yield in the detection and characterization of cystic masses.
• Intracranial cysts and ventriculomegaly also may be detected and characterized by transcranial ultrasound through a burr hole.²³

Angiography

Findings

Imaging pearls

• Findings on angiography indicate that there is a higher incidence of an absence of the middle cerebral vein in patients with arachnoid cysts of the middle fossa, as compared with the general population.
• Angiographic findings indicate that among patients with arachnoid cysts of the middle fossa, there is a decrease in drainage of the middle cerebral vein into the cavernous sinus on the side of the cyst.

Multimedia

Media file 1: T2-weighted sagittal MRI image (see Image below for axial view) of the brain in a 28-year-old woman with an incidental finding of a superior cerebellar cistern arachnoid cyst (arrow).

Media file 2: T2-weighted axial MRI image (see Image above for sagittal view) of the brain in a 28-year-old woman with an incidental finding of a superior cerebellar cistern arachnoid cyst (arrow).

Media file 3: Unenhanced CT scan of the head in a 26-year-old man with a history of seizures since childhood (same patient as in Image below). The scan shows a large left frontoparietal cyst with a mass effect. The cyst was resected, and histologic analysis confirmed an arachnoid cyst.

Media file 4: Unenhanced CT scan of the head in a 26-year-old man with a history of seizures since childhood (same patient as in Image above). The scan shows a large left frontoparietal cyst with a mass effect. The cyst was resected, and histologic analysis confirmed an arachnoid cyst.

Media file 5: Axial T2-weighted MRI image through the midbrain, showing a right middle cranial fossa homogeneous lesion (same lesion as in Image below) with CSF signal intensity and no perceptible wall or internal complexity. There is associated remodeling of the adjacent sphenoid bone and brain displacement. These imaging features are typical of an arachnoid cyst.

Media file 6: Axial T2-weighted MRI image through the body of the lateral ventricles, showing superior extension of a right middle cranial fossa lesion (same lesion as in Image above). The lesion is homogeneous, with no perceptible wall, no internal complexity, and CSF signal intensity. There is associated remodeling of the adjacent calvarium and brain displacement. These imaging features are typical of an arachnoid cyst.

Media file 7: Coronal T1-weighted MRI image through a brain lesion (same lesion as in Images 5-6, 8), showing homogeneity of the lesion, lack of a perceptible wall, lack of internal complexity, and CSF signal intensity. There is associated remodeling of the adjacent calvarium and brain displacement. These imaging features are typical of an arachnoid cyst.

Media file 8: Sagittal fluid-attenuated inversion recovery (FLAIR) weighted image through a brain lesion (same lesion as shown in Images 5-7), showing homogeneity of the lesion, lack of a perceptible wall, lack of internal complexity, and CSF signal intensity. There is associated remodeling of the adjacent sphenoid bone and brain displacement. These imaging features are typical of an arachnoid cyst.

Media file 9: Prenatal coronal T1-weighted MRI images through the middle cranial fossa, showing a left temporal fossa homogeneous lesion (postnatal images of same patient shown in Images below) with CSF signal intensity and no perceptible wall or internal complexity. There is associated displacement of adjacent brain. These imaging features are typical of an arachnoid cyst.

Media file 10: Postnatal coronal T2-weighted MRI images through the middle cranial fossa, showing a left temporal fossa homogeneous lesion (prenatal images of same patient shown in Images above and below) with CSF signal intensity and no perceptible wall or internal complexity. There is associated remodeling of adjacent calvarium, brain displacement, and a midline shift. These imaging features are typical of an arachnoid cyst.

Media file 11: Postnatal coronal T1-weighted MRI images through the middle cranial fossa, showing a left temporal fossa homogeneous lesion (prenatal images of same patient shown in Image above) with CSF signal intensity and no perceptible wall or internal complexity. There is associated remodeling of adjacent calvarium, brain displacement, and a midline shift. These imaging features are typical of an arachnoid cyst.

References

1. Van Tassel P, Cure JK. Nonneoplastic intracranial cysts and cystic lesions. Semin Ultrasound CT MR. Jun 1995;16(3):186-211. [Medline].

2. Algin O, Hakyemez B, Gokalp G, Korfali E, Parlak M. Phase-contrast cine MRI versus MR cisternography on the evaluation of the communication between intraventricular arachnoid cysts and neighbouring cerebrospinal fluid spaces. Neuroradiology. May 2009;51(5):305-12. [Medline].

3. Spacca B, Kandasamy J, Mallucci CL, Genitori L. Endoscopic treatment of middle fossa arachnoid cysts: a series of 40 patients treated endoscopically in two centres. Childs Nerv Syst. Jul 24 2009;[Medline].

4. Orrison WW, Hanson EH, Alamo T, Watson D, Sharma M, Perkins TG, et al. Traumatic brain injury: a review and high-field MRI findings in 100 unarmed combatants using a literature-based checklist approach. J Neurotrauma. May 2009;26(5):689-701. [Medline].

5. Bilginer B, Onal MB, Oguz KK, Akalan N. Arachnoid cyst associated with subdural hematoma: report of three cases and review of the literature. Childs Nerv Syst. Jan 2009;25(1):119-24. [Medline].

6. Pillai P, Menon SK, Manjooran RP, Kariyattil R, Pillai AB, Panikar D. Temporal fossa arachnoid cyst presenting with bilateral subdural hematoma following trauma: two case reports. J Med Case Reports. Feb 9 2009;3:53. [Medline].

7. Szucs A, Várady P, Pestality P, Dániel F, Lalit N, Kenéz J. Occlusive hydrocephalus caused by a fourth ventricle arachnoid cyst. Ideggyogy Sz. Jan 30 2008;61(1-2):54-8. [Medline].

8. Bonde V, Muzumdar D, Goel A. Fourth ventricle arachnoid cyst. J Clin Neurosci. Jan 2008;15(1):26-8. [Medline].

9. Aicardi J, Bauman F. Supratentorial extracerebral cysts in infants and children. J Neurol Neurosurg Psychiatry. Jan 1975;38(1):57-68. [Medline].

10. Utsunomiya H, Yamashita S, Takano K. Midline cystic malformations of the brain: imaging diagnosis and classification based on embryologic analysis. Radiat Med. Jul 2006;24(6):471-81.

11. Ashker L, Weinstein JM, Dias M, Kanev P, Nguyen D, Bonsall DJ. Arachnoid cyst causing third cranial nerve palsy manifesting as isolated internal ophthalmoplegia and iris cholinergic supersensitivity. J Neuroophthalmol. Sep 2008;28(3):192-7. [Medline].

12. Cayli SR. Arachnoid cyst with spontaneous rupture into the subdural space. Br J Neurosurg. Dec 2000;14(6):568-70. [Medline].

13. Kivrak AS, Koc O, Emlik D, Kiresi D, Odev K, Kalkan E. Differential diagnosis of dumbbell lesions associated with spinal neural foraminal widening: Imaging features. Eur J Radiol. May 14 2008;[Medline].

14. Voyadzis JM, Bhargava P, Henderson FC. Tarlov cysts: a study of 10 cases with review of the literature. J Neurosurg. Jul 2001;95(1 Suppl):25-32. [Medline].

15. Anderson FM, Landing BH. Cerebral arachnoid cysts in infants. J Pediatr. Jul 1966;69(1):88-96. [Medline].

16. Hughes G, Ugokwe K, Benzel EC. A review of spinal arachnoid cysts. Cleve Clin J Med. Apr 2008;75(4):311-5. [Medline].

17. Tsutsumi S, Kondo A, Yasumoto Y, Ito M. Asymptomatic huge congenital arachnoid cyst successfully treated by endoscopic surgery--case report. Neurol Med Chir (Tokyo). Sep 2008;48(9):405-8. [Medline].

18. Zeng L, Feng L, Wang J, Li J, Wang Y, Chen J, et al. Comparative study on two surgical procedures for middle cranial fossa arachnoid cysts. J Huazhong Univ Sci Technolog Med Sci. Aug 2008;28(4):431-4. [Medline].

19. Kollias SS, Bernays RL. Interactive magnetic resonance imaging-guided management of intracranial cystic lesions by using an open magnetic resonance imaging system. J Neurosurg. Jul 2001;95(1):15-23. [Medline].

20. Hu XY, Hu CH, Fang XM, Cui L, Zhang QH. Intraparenchymal epidermoid cysts in the brain: diagnostic value of MR diffusion-weighted imaging. Clin Radiol. Jul 2008;63(7):813-8. [Medline].

21. Secer HI, Anik I, Celik E, Daneyemez MK, Gonul E. Spinal hydatid cyst mimicking arachnoid cyst on magnetic resonance imaging. J Spinal Cord Med. 2008;31(1):106-8. [Medline].

22. Herman-Sucharska I, Urbanik A. [MRI of fetal central nervous system malformations]. Przegl Lek. 2007;64(11):917-22. [Medline].

23. Slovis TL, Canady A, Touchette A, Goldstein A. Transcranial sonography through the burr hole for detection of ventriculomegaly. A preliminary report. J Ultrasound Med. Apr 1991;10(4):195-200. [Medline].

24. Krings T, Lukas R, Reul J, et al. Diagnostic and therapeutic management of spinal arachnoid cysts. Acta Neurochir (Wien). 2001;143(3):227-34; discussion 234-5. [Medline].

25. Martin AJ, Jarosz JM, Thomas NW. The strange association of pneumosinus dilatans and arachnoid cyst: case report and review of the literature. Acta Neurochir (Wien). 2001;143(2):197-201. [Medline].

Keywords

arachnoid cyst, glioependymal cyst, meningeal cyst, intra-arachnoid cerebrospinal fluid–containing cysts, intracranial mass, leptomeningitis, arachnoid diverticula, spinal arachnoid cysts, intradural spinal arachnoid cysts, agenesis of corpus callosum, kyphoscoliosis, myelodysplasia, spinal dysraphism, intracystic hemorrhage, subdural hygroma, subdural hematoma, calvarial bulging, intracranial hypertension, craniomegaly, developmental delay, visual loss, precocious puberty, seizures, focal neurologic signs, temporal lobe agenesis, supratentorial cysts, chronic subdural hematomas, pneumosinus dilatans of sphenoid sinus, Cockayne syndrome, Menkes disease, spinal cord displacement, spinal cord compression, epidural arachnoid cysts

Contributor Information and Disclosures

Author

Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, Consultant Radiologist and Honorary Professor, North Manchester General Hospital Pennine Acute NHS Trust, UK
Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR is a member of the following medical societies: American Association for the Advancement of Science, American Institute of Ultrasound in Medicine, British Medical Association, British Society of Interventional Radiology, Royal College of Physicians, Royal College of Physicians and Surgeons of the United States, Royal College of Radiologists, and Royal College of Surgeons of England
Disclosure: Nothing to disclose.

Coauthor(s)

Ian Turnbull, MB, ChB, MD, DMRD, FRCR, Lecturer, Department of Radiology, University of Manchester; Consulting Neuroradiologist, Hope Hospital, Salford, Manchester and North Manchester General Hospital, UK
Disclosure: Nothing to disclose.

Riyadh Al-Okaili, MBBS, Interventional/Therapeutic and Diagnostic Neuro-Radiologist, King Abdulaziz Medical City
Riyadh Al-Okaili, MBBS is a member of the following medical societies: American College of Radiology
Disclosure: Nothing to disclose.

Sumaira MacDonald, MBChB, PhD, MRCP, FRCR, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute
Sumaira MacDonald, MBChB, PhD, MRCP, FRCR is a member of the following medical societies: British Medical Association, Royal College of Physicians, and Royal College of Radiologists
Disclosure: Nothing to disclose.

Khalid Mahmood, MBBS, FCPS, Locum Appointment Training Specialist Registrar, Department of Radiology - Paediatric, Royal Liverpool (Alder Hey) Children's Hospital
Disclosure: Nothing to disclose.

Medical Editor

Lucien M Levy, MD, PhD, Director of Neuroradiology, Professor of Radiology, Department of Radiology, George Washington University Medical Center
Lucien M Levy, MD, PhD is a member of the following medical societies: American Cancer Society, American College of Radiology, American Heart Association, American Medical Association, American Roentgen Ray Society, American Society of Neuroradiology, and Radiological Society of North America
Disclosure: Nothing to disclose.

Pharmacy Editor

Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand
Disclosure: Nothing to disclose.

CME Editor

Robert M Krasny, MD, Resolution Imaging Medical Corporation
Robert M Krasny, MD is a member of the following medical societies: American Roentgen Ray Society and Radiological Society of North America
Disclosure: Nothing to disclose.

Chief Editor

James G Smirniotopoulos, MD, Professor of Radiology, Neurology, and Biomedical Informatics, Chairman, Department of Radiology and Radiological Sciences, Uniformed Services University of the Health Sciences
James G Smirniotopoulos, MD is a member of the following medical societies: American College of Radiology, American Roentgen Ray Society, American Society of Head and Neck Radiology, American Society of Neuroradiology, American Society of Pediatric Neuroradiology, Association of University Radiologists, and Radiological Society of North America
Disclosure: Nothing to disclose.

Related eMedicine topics

Neoplasms, Spinal Cord

Arachnoiditis

Trisomy 18

MR Imaging, Temporal Bone

Precocious Puberty

© 1994- by Medscape.
All Rights Reserved
(http://www.medscape.com/public/copyright)