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.
More on Arachnoid Cyst |
| Overview: Arachnoid Cyst |
 Imaging: Arachnoid Cyst |
| Multimedia: Arachnoid Cyst |
| References |
| Further Reading |
| « Previous Page | Next Page » |
References
Van Tassel P, Cure JK. Nonneoplastic intracranial cysts and cystic lesions. Semin Ultrasound CT MR. Jun 1995;16(3):186-211. [Medline].
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].
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].
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].
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].
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].
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].
Bonde V, Muzumdar D, Goel A. Fourth ventricle arachnoid cyst. J Clin Neurosci. Jan 2008;15(1):26-8. [Medline].
Aicardi J, Bauman F. Supratentorial extracerebral cysts in infants and children. J Neurol Neurosurg Psychiatry. Jan 1975;38(1):57-68. [Medline].
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.
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].
Cayli SR. Arachnoid cyst with spontaneous rupture into the subdural space. Br J Neurosurg. Dec 2000;14(6):568-70. [Medline].
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].
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].
Anderson FM, Landing BH. Cerebral arachnoid cysts in infants. J Pediatr. Jul 1966;69(1):88-96. [Medline].
Hughes G, Ugokwe K, Benzel EC. A review of spinal arachnoid cysts. Cleve Clin J Med. Apr 2008;75(4):311-5. [Medline].
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].
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].
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].
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].
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].
Herman-Sucharska I, Urbanik A. [MRI of fetal central nervous system malformations]. Przegl Lek. 2007;64(11):917-22. [Medline].
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].
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].
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].
Further Reading
Related eMedicine topics
Neoplasms, Spinal Cord
Arachnoiditis
Trisomy 18
MR Imaging, Temporal Bone
Precocious Puberty
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
