AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

INTRODUCTION

Section 2 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

Background

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

Arachnoid cysts also occur within the spinal canal, in which 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.

Arachnoid cysts often are an incidental finding on imaging, and usually, patients are asymptomatic even if the cyst is quite large. The most commonly associated clinical features are headache, calvarial bulging, and seizures, with focal neurologic signs occurring less frequently. Controversy surrounds the treatment of arachnoid cysts. Some clinicians advocate treating only patients with symptomatic cysts, while others believe that even in asymptomatic patients, 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.

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, while 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, with hyaline change at times. No epithelial lining is present. The outer wall of the cyst adheres loosely to the dura. The cyst wall is devoid of blood vessels, and changes of inflammation or hemorrhage seldom occur.

Arachnoid cysts usually occur in association with normal arachnoid cisterns, and 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 because of intracranial pulsation pushing CSF through defects (which behave like valves) to become entrapped in arachnoid locations or, less likely, because of fluid secretion by the cyst wall 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. A few cysts may contain elevated protein content. Gross appearances of glioependymal cysts usually are 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, subarachnoid hemorrhage, or neonatal infections and can 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 due to 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 become space occupying 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. Recently, 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—in particular, anteriorly and the parasagittal location in the interhemispheric fissure. Most cysts are unilateral, smoothly rounded, and adhere loosely to the dura. Arachnoid cysts can 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 (which may produce endocrinopathy), the cerebellopontine angle (11%), the quadrigeminal plate cistern (10%) in relationship to the vermis (9%), and 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 and, less frequently, at the lumbosacral or sacral level.

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

Frequency

United States

Arachnoid cysts constitute 1% of intracranial masses, with 50-60% occurring in the middle cranial fossa.

Mortality/Morbidity

Morbidity and mortality depend on the location of the arachnoid cyst and complications, such as acute mass effect by intracystic hemorrhage or the development of a subdural hygroma/hematoma. The exact incidence of mortality and morbidity from an arachnoid cyst is not known.

Sex

The male-to-female ratio is 4:1.

Age

Patients who are symptomatic for arachnoid cysts can present at any age.

Clinical Details

Arachnoid cysts often are an incidental finding on imaging, and patients usually are asymptomatic even if the cyst is quite large. The most common associated clinical features include headache, calvarial bulging, intracranial hypertension, craniomegaly, developmental delay, visual loss, precocious puberty, and seizures, with focal neurologic signs occurring less frequently. Arachnoid cysts are known to rupture into the subdural space or undergo intracystic hemorrhage.

Anderson and Landing¹ and Aicardi and Bauman² described the clinicopathologic features of supratentorial cysts in infancy. Neither a history of antecedent trauma nor the clinical features of preceding cranial trauma were noted in the infants. The infants had a tense fontanellle 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. Middle cranial fossa cysts have been linked to ipsilateral chronic subdural hematomas. Rarely, they may communicate with the subdural space, forming a slitlike extension over the hemispheric surface.

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

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, and although symptomatic arachnoid cysts are comparatively rare in infants, ultrasound provides a noninvasive imaging technique with high yield in the detection and characterization of cystic masses.

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

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 Differential Diagnosis, below). The confusion is much more likely to occur with CT. CT attenuation values and signal intensities parallel those of CSF, but difficulties may be encountered in cases of hemorrhagic cysts.

The most important differentiation to make is between arachnoid and epidermoid cysts; MRI diffusion-weighted images (DWIs) make differentiating the 2 masses easier. Some arachnoid cysts may contain proteinaceous fluid or blood, and 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.

DIFFERENTIALS

Section 3 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

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 and often are bilateral and 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 and readily identified by associated 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)

RADIOGRAPH

Section 4 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

Findings

Intracranial

• Forward bowing of the anterior cranial wall of the middle cranial fossa and elevation of the sphenoidal ridge have been reported on skull radiographs in 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.

Degree of Confidence

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

False Positives/Negatives

Forward bowing of the anterior cranial wall of the middle cranial fossa and elevation of the sphenoidal ridge are difficult to assess and occasionally may be difficult to differentiate from normal. Other conditions, such as neurofibromatosis type I, can mimic these changes.

In infants, craniomegaly associated with widening of the fontanelle and thinning of the calvarium may be a normal variant and associated with other intracranial pathology.

Spinal canal widening and erosion of the pedicles has a wide differential diagnosis, including spinal cord tumors.

CT SCAN

Section 5 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

Findings

Intracranial

• Arachnoid cysts typically show compression of the subarachnoid space by a cystic structure that may be unilocular or septate and of variable size, although the septa may not always be visible.

• The subjacent brain shows minimal mass effect.

• On CT scans, arachnoid cysts are characterized by sharp nonenhancing borders and are isodense to CSF.

• On a bone window, remodeling of the skull may be evident.

• Arachnoid cysts seldom calcify.

• CT cisternography can show a smooth outer surface in arachanoid cysts, 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, with some cysts filling with contrast immediately and others showing either delayed contrast accumulation or no filling.

• 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

• 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 and demonstrates bone detail well.

Degree of Confidence

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 and demonstrates bone detail well. CT myelography remains of diagnostic value, especially for arachnoid cysts that are not definitive on MRI.

False Positives/Negatives

There is a wide differential diagnosis for both intracranial and intraspinal cystic lesions, and arachnoid cysts have several mimics. Difficulties are encountered particularly with hemorrhagic arachnoid cysts when the cyst contents are no longer isodense to CSF.

MRI

Section 6 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

Findings

Intracranial

• On MRI, arachnoid cysts appear as well-defined nonenhancing intracranial masses that are isointense to CSF.



• Diagnostic confusion occasionally may arise 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 recently 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. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. 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 troublemovingorstraightening 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 may contain proteinaceous fluid or blood, and signal loss on DWI may not be marked, which 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, whereas that signal is typically higher in an epidermoid cyst.



• 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 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 and/or spinal cord compression.



• The cyst is usually hyperintense to CSF on T2-weighted sequences because of the relative lack of CSF pulsation artifacts.

Degree of Confidence

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 localization, extent, and relationship of the arachnoid cyst to the brain and spinal cord.

False Positives/Negatives

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

ULTRASOUND

Section 7 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

Findings

Cranial ultrasonography is an important diagnostic tool during the first year of life and is limited by the closure of the anterior fontanelle, which normally occurs in full-term infants aged 9-18 months. Although infants with arachnoid cysts rarely are symptomatic, ultrasound provides a noninvasive imaging technique with a high yield in the detection and characterization of cystic masses. Intracranial cysts and ventriculomegaly also can be detected and characterized by transcranial ultrasound through a burr hole.

ANGIOGRAPHY

Section 8 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

Findings

Angiography in patients with middle fossa arachnoid cysts, as compared to the general population, shows a greater incidence of absence of the middle cerebral vein or decreased drainage of the middle cerebral vein into the cavernous sinus on the side of the cyst.

INTERVENTION

Section 9 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

Medical/Legal Pitfalls

• Every effort must be made to reliably detect arachnoid cysts because most arachnoid cysts are an incidental finding and patients are asymptomatic. Differentiation must be made from the more serious cystic intracranial and intraspinal tumors. Larger arachnoid cysts should be considered for serial scans because they may show progressive enlargement, and patients may become candidates for surgical consideration.

MULTIMEDIA

Section 10 of 11  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

Media file 1:  T2-weighted sagittal MRI image (see Image 2 for axial view) of the brain in a 28-year-old woman with an incidental finding of a superior cerebellar cistern arachnoid cyst (arrow).
	View Full Size Image
Media type:  MRI

Media file 2:  T2-weighted axial MRI image (see Image 1 for sagittal view) of the brain in a 28-year-old woman with an incidental finding of a superior cerebellar cistern arachnoid cyst (arrow).
	View Full Size Image
Media type:  MRI

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 4). The scan shows a large left frontoparietal cyst with a mass effect. The cyst was resected, and histologic analysis confirmed an arachnoid cyst.
	View Full Size Image
Media type:  CT

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 3). The scan shows a large left frontoparietal cyst with a mass effect. The cyst was resected, and histologic analysis confirmed an arachnoid cyst.
	View Full Size Image
Media type:  CT

Media file 5:  Axial T2-weighted MRI image through the midbrain, showing a right middle cranial fossa homogeneous lesion (same lesion as in Images 6-8) 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.
	View Full Size Image
Media type:  MRI

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 shown in Images 5, 7-8). 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.
	View Full Size Image
Media type:  MRI

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.
	View Full Size Image
Media type:  MRI

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.
	View Full Size Image
Media type:  MRI

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 10-11) 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.
	View Full Size Image
Media type:  MRI

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 Image 9) 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.
	View Full Size Image
Media type:  MRI

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 9) 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.
	View Full Size Image
Media type:  MRI

REFERENCES

Section 11 of 11

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Angiography
• Intervention
• Multimedia
• References

1. Anderson FM, Landing BH. Cerebral arachnoid cysts in infants. J Pediatr. Jul 1966;69(1):88-96. [Medline].
2. Aicardi J, Bauman F. Supratentorial extracerebral cysts in infants and children. J Neurol Neurosurg Psychiatry. Jan 1975;38(1):57-68. [Medline].
3. Cayli SR. Arachnoid cyst with spontaneous rupture into the subdural space. Br J Neurosurg. Dec 2000;14(6):568-70. [Medline].
4. Friede RL. Meningeal cysts. In: Developmental Neuropathology. Berlin: Springer-Verlag;1989:209-19.
5. 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].
6. 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].
7. 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].
8. 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].
9. 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.
10. Van Tassel P, Cure JK. Nonneoplastic intracranial cysts and cystic lesions. Semin Ultrasound CT MR. Jun 1995;16(3):186-211. [Medline].
11. 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].

Article Last Updated: Apr 3, 2007