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Neuroradiology Case of the Week
Case 265
Sarah Goldfeder, MD, and P-L Westesson, MD, PhD, DDS
Clinical
Presentation: Patient is a
newborn term infant presenting with evidence of hydrocephalus detected on prenatal ultrasound.
Imaging Findings:
Head CT: The right lateral ventricle is dilated with the atrium measuring 2.0 cm. The left lateral, third, and fourth ventricles are normal in size. There is no intraventricular hemorrhage or mass seen. There is no dysmorphic brain parenchyma, parenchymal bleed, or infarct.
Brain MR: There is gross dilatation of the right lateral ventricle. The left lateral, third, and fourth ventricles are normal. There is no periventricular fluid. There is mild white matter volume loss on the right side; however, the brain parenchyma shows normal signal intensity and normal myelination. There is no abnormal parenchymal mass or enhancing lesion. There is loss of flow void of the right foramen of Monro indicating obstruction. There is a possible arachnoid cyst in the third ventricle responsible for the obstruction of CSF flow. Other flow voids in the brain are normal.
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Figure 1: CT head. Dilatation of right lateral ventricle.
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Figure 2: T1W post contrast MR. Mild white matter volume loss on the right side, in the region of the posterior horn of the lateral ventricle.
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Figures 3-5 below are sequential axial FLAIR MR images that demonstrate obstruction of CSF flow through the right foramen of Monro. |
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| Figure 3 shows dilatation of right lateral ventricle. |
Figure 4 shows the right foramen of Monro ending abruptly, not pointing towards the third ventricle. The left foramen of Monro points in the direction of the third ventricle, consistent with normal, unobstructed flow of CSF. |
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| Figure 5 shows a probable arachnoid cyst in the third ventricle with obstruction of the right foramen of Monro. |
Diagnosis: Unilateral hydrocephalus due to obstruction of the foramen of Monro
Discussion: Unilateral hydrocephalus (UH) is an uncommon disorder of the newborn. Overall, congenital hydrocephalus occurs between 1.8 and 3 per 1000 live births; however, the vast majority of these cases are bilateral, symmetric hydrocephalus. Bilateral, symmetric hydrocephalus has a high rate of association with CNS and extra-CNS anomalies and a mortality rate up to 85%. In contrast, unilateral hydrocephalus is less frequently associated with other anomalies, and if no other anomalies are present, the survival rate is 70%.
First described by Von Mohr in 1842, the etiology for UH is usually due to obstruction of the foramen of Monro, which may be congenitally atretic, stenotic, or occluded by a membrane. Acquired etiologies for an obstructed foramen of Monro include thalamic and intraventricular neoplasms, colloid cysts, tuberculous masses, ventriculitis, vascular malformations, and non-specific inflammatory conditions. While not commonly associated with other anomalies, UH can be seen in conjunction with agenesis of the corpus callosum, hemihypertrophy, and frontoethmoid encephalocele.
Unilateral hydrocephalus is rarely diagnosed on prenatal ultrasound. Since UH is so rare, a dilated ventricle is often assumed to be bilateral and symmetric even when the near-field ventricle is obscured by sonographic artifact or noise. Additionally, pseudohydrocephalus may be diagnosed when the hypoechoic cortex is misinterpreted as a dilated ventricle or pseudoepidural artifacts appear as fluid collections. MR and CT imaging can aid in a definitive diagnosis.
When UH is detected prenatally, it is important to determine the cause. If the venticulomegaly is an isolated finding, then emergent surgical intervention may not be required, and, with careful monitoring, the delivery may be delayed to allow for lung maturation. However, if there is progressive ventricular dilatation, cortical thinning, or abnormal rapid intracranial growth, then surgical intervention is warranted. Ventriculoperitoneal shunting in the first month of life is critical in order to prevent thinning of the cortical mantle and poor neurologic outcome. Endoscopic fenestration of the septum pellucidum may be applicable in cases of inflammatory and membranous occlusion of the foramen of Monro.
In conclusion, unilateral hydrocephalus is a rare entity that has far fewer associated anomalies, and much improved survival rate and neurologic prognosis, than the more common bilateral, symmetric hydrocephalus.
References:
- Schulman H, Landau D, Schulman P, Hertzanu Y. Congenital unilateral hydrocephalus--CT findings. Eur J Radiol. 2000 Dec;36(3):161-4. [Medline]
- Patten RM, Mack LA, Finberg HJ. Unilateral hydrocephalus: prenatal sonographic diagnosis. AJR Am J Roentgenol. 1991 Feb;156(2):359-63. [Medline]
- Koga Y, Tahara Y, Kida T, Matumoto Y, Negishi H, Fujimoto S. Prenatal diagnosis of congenital unilateral hydrocephalus. Pediatr Radiol. 1997 Apr;27(4):319-20. [Medline]
- Durfee SM, Kim FM, Benson CB. Postnatal outcome of fetuses with prenatal diagnosis of asymmetric hydrocephalus. J Ultrasound Med. 2001 Mar;20(3):263-8. [Medline]
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