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OBSTETRIC RADIOLOGY Table of Contents   
Year : 2007  |  Volume : 17  |  Issue : 2  |  Page : 69-70
Signs: The "Keyhole" sign in antenatal ultrasound

Dept. of Radiodiagnosis, Rural Medical College, Pravara Institute of Medical Sciences, Loni, India

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How to cite this article:
Aironi V D, Gandage S G, Kashyape R S, Vyas V R. Signs: The "Keyhole" sign in antenatal ultrasound. Indian J Radiol Imaging 2007;17:69-70

How to cite this URL:
Aironi V D, Gandage S G, Kashyape R S, Vyas V R. Signs: The "Keyhole" sign in antenatal ultrasound. Indian J Radiol Imaging [serial online] 2007 [cited 2021 Feb 28];17:69-70. Available from:

   Case Report Top

A 22-years-old woman with a 28 - weeks pregnancy came for her first antenatal ultrasound (USG) check up. On examination of the fetal head, a midline and deeply situated, interhemispheric, spherical, anechoic cyst extending from the thalami to a tubular channel was seen, resembling a "keyhole" [Figure - 1],[Figure - 2]. This cystic intracranial lesion showed high frequency Doppler signals on color Doppler examination [Figure - 3],[Figure - 4]. There was no ventriculomegaly and no other congenital defect in the fetus.

This keyhole sign is pathognomonic of an arteriovenous malformation (AVM) arising from the vein of Galen. The cyst represents the aneurysmal vein of Galen and the tubular channel represents the straight sinus. These two structures collectively look like a keyhole.

   Discussion Top

The "keyhole sign" is a gray scale usg 0 finding. The vein of Galen aneurysm is actually an intracranial AVM involving the vein of Galen. [1],[2],[3] It is detected on antenatal USG, usually after 32 weeks of gestation. A color Doppler examination reveals high velocity pulsatile arterial flow in the lesion. [1],[3],[4],[5],[6],[7]

A vein of Galen AVM may lead to congestive heart failure in the first week of life and in many; the correct diagnosis is made only at this time or at autopsy. [3] With widespread use of antenatal USG, most cases of vein of Galen AVM are currently detected in utero. [3]

The differential diagnosis includes choroid plexus cyst, tumor, a high riding III ventricle in agenesis of the corpus callosum, dorsal cyst in holoprosencephaly and porencephalic cyst. [1] These conditions can be excluded by color Doppler, which reveals absence of color flow in all these lesions. [1] In agenesis of the corpus callosum, radiating sulci can be seen extending away from the dilated high-riding third ventricle. [1]

A vein of Galen AVM may be associated with hydrocephalus due to compression of the aqueduct of Sylvius and resultant macrocephaly. [1] Associated porencephalic cysts may be seen due to decreased blood supply to the brain as result of the AV shunt. [1] The fetus may develop hydrops fetalis as a result of high output cardiac failure, in which case the prognosis is grim. [1] Associated prenatal USG features are present in 76% of fetuses, including cardiomegaly (64%), enlarged neck vessels (32%) and ventriculomegaly (24%). [3] If the baby presents without cardiac failure and hydrops, the prognosis is good. [2] The lesion can be managed by catheter embolization with liquid acrylic embolic agents or fibered coils following delivery, after which the prognosis is excellent. [2],[6]

   References Top

1.Ultrasound in Obstetrics and Gynecology. By Dewbury K, Cosgrove D. Churchill Livingstone: 1993. p. 302-3.  Back to cited text no. 1    
2.Jones BV, Ball WS, Tomsick TA, Millard J, Crone KR. Vein of galen aneurysmal malformation: Diagnosis and treatment of 13 children with extended clinical follow up. AJNR Am J Neuroradiol 2002;23:1717-24.  Back to cited text no. 2  [PUBMED]  [FULLTEXT]
3.Sepulveda W, Vanderheyden T, Pather J, Pasquini L. Vein of galen malformation: Prenatal evaluation with three-dimensional power Doppler angiography. J Ultrasound Med 2003;22:1395-8.  Back to cited text no. 3  [PUBMED]  [FULLTEXT]
4.Color Doppler Sonography in Obstetrics. Emerson D. In : Sonography in Obstetrics and Gynecology: Principles and Practice. Fleischer AC, Manning FA, Jeanty P, Romero R, editor. 5 th ed. Appleton and Lange Publication: 1996. p. 303  Back to cited text no. 4    
5.Ultrasonography in Obstetric and Gynecology. Callen PW, 4 th ed. W.B Saunders Publication: 2000. p. 300.  Back to cited text no. 5    
6.Diagnostic Ultrasound, Vol. 2, Rumack CM. 3 rd ed. Mosby Publication: 2005. p. 1264, 1265, 1547, 1549.  Back to cited text no. 6    
7.Sepulveda W, Platt CC, Fisk NM. Prenatal diagnosis of cerebral arteriovenous malformation with color Doppler Ultrasonography: Case report and review of literature. Ultrasound Obstet Gynecol 1995;6:282-6.  Back to cited text no. 7    

Correspondence Address:
R S Kashyape
Dept of Radiodiagnosis, Rural Medical College, Pravara Institute of Medical Sciences, Loni - 413 736, BK, Ahmednagar. Maharashatra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0971-3026.33611

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  [Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4]


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