Polihydramnios

Polyhydramnios

http://emedicine.medscape.com/article/404856-overview

Polyhydramnios
Author: Prabhakar Rajiah, MD, MBBS, FRCR; Chief Editor: Eugene C Lin, MD more... Updated: May 25, 2011

Overview
Polyhydramnios is the presence of excess amniotic fluid in the uterus. By definition, polyhydramnios is diagnosed if the deepest vertical pool is more than 8 cm or amniotic fluid index (AFI) is morethan 95th percentile for the corresponding gestational age. With a deep pocket of 8 cm as criteria of polyhydramnios, the incidence is 1-3% of all pregnancies. About 20% are associated with fetal anomalies. Polyhydramnios has a variety of causes affecting the mother or the fetus. The presence of polyhydramnios should prompt a search for other fetal anomalies. Some of the anomalies can be diagnosedwith sonography, while others require karyotyping.

Preferred examination
The diagnostic approach to polyhydramnios consists of (1) physical examination of the mother with an investigation for diabetes mellitus, diabetes insipidus, and Rh isoimmunization; (2) sonographic confirmation of polyhydramnios and assessment of the fetus; (3) fetal karyotyping; and (4) maternal serologic testing forsyphilis.

Limitations of techniques
Clinical examination can reveal a uterine size larger than that expected for the corresponding gestational age of the fetus. Ultrasonography is the most reliable method for diagnosing and quantifying polyhydramnios. Experienced operators make the diagnosis based on subjective assessment. The height of the deepest pocket and the AFI are objective semiquantitativemeasurements of the amniotic fluid. MRI is not necessary for the diagnosis of polyhydramnios, but polyhydramnios can be detected during MRI for other indications. Three limitations of MRI are notable. First, MRI is not cost effective. Second, it is time consuming. For example, the time required for magnetic resonance volumetry can be as long as 6 hours, which is not ideal when sonography can beperformed in only a few minutes. Third, MRI requires knowledge of computers and postprocessing.

Computed Tomography
CT scanning is generally avoided during pregnancy.

Magnetic Resonance Imaging
MRI is not essential in the imaging protocol for polyhydramnios, but if it is performed for fetal or maternal imaging, it can also be used for diagnosing polyhydramnios. A customized medical imagepostprocessing software package can be used for segmentation and 3-dimensional (3D) modeling. Once the structures of interest in a 3D image volume are segmented, the postprocessing software creates a corresponding 3D surface model and automatically calculates the volume of each 3D reconstruction Although allowances must be made for a smaller fluid volume (except in polyhydramnios) and for segmentation of theamniotic fluid in vivo being slightly more difficult owing to fetal motion, volumetric measurements are likely to represent the real values.

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20-02-2012 12:57

Polyhydramnios

http://emedicine.medscape.com/article/404856-overview

Degree of confidence
MRI is good for assessing the volume of amniotic fluid and for diagnosing polyhydramnios. However, MRI is not mandatory for the diagnosis ofpolyhydramnios. Kubik et al found that MRI is accurate in measuring the amniotic fluid volume, as it is in measuring placental volume and fetal weight.
[1]

A good correlation was obtained between MR volumetry studies and the actual amniotic fluid volume. Although this would not be a cost effective method of diagnosing polyhydramnios, it would be of greater help in monitoring therapeutic responseto polyhydramnios treatment. The common sequences used are T2-weighted single-shot fast spin-echo and high-spatial-resolution T1-weighted fast spin-echo images subsequent to a spoiled gradient-echo localizer.

False positives/negatives
Measuring the amniotic fluid volume is difficult when the quantity is low because no difference in signal intensity can be noted between a thin rim of fluid and...