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Meckel-Gruber Syndrome

Enlarged cystic-dysplastic kidneys

Occipital encephalocele

Findings:

Bilaterally enlarged cystic kidneys were seen filling the fetal abdomen. Virtually no amniotic fluid was identified. In addition, an occipital encephalocele was seen. This constellation of findings is consistent with the Meckel-Gruber syndrome.

Discussion:

The finding of large kidneys with multiple small cysts in addition to an encephalocele makes the diagnosis of the Meckel-Gruber syndrome quite certain. This syndrome consisting of cystic dysplastic kidneys, occipital encephalocele and polydactyly was first described by Meckel in 1822 and was subsequently referred to as "dysencephalia splanchnocystica" by Gruber in 1934. This inheritance of this syndrome, autosomal recessive was subsequently reported in 1969 by Poitz and Howe. A variety of malformations may be associated with this syndrome but most investigators agree that cystic renal dysplasia must be present with at least one of the other two anomalies in the classic "triad": central nervous system abnormalities ie occipital encephalocele and polydactyly. One group, Blackenberg et al have stated that hepatic fibrosis is also a consistent finding on the basis of clinicopathologic findings. Other associated malformations which have been reported include: microcephaly, micrognathia, cleft palate, cardiac malformations including rotational abnormalities, ventriculoseptal defect, aortic hypoplasia or coarctation and aortic valvular stenosis, musculoskeletal abnormalities including: webbd neck, club foot, syndactyly and clinodactyly and accessory spleens.

As was mentioned above, the renal abnormalities are the most consistent and constant feature of the syndrome. The kidneys are markedly enlarged with macroscopic cysts. There is debate as to which form of cystic dysplasia the renal abnormalities most resemble. Some believe the findings are most similar to autosomal recessive kidney disease while others believe that the renal abnormality is multicystic renal dysplasia with markedly defective nephron differentiation. Other renal abnormalites that have been associated with Meckel-Gruber syndrome include renal agenesis, hypoplasia and duplication. The hepatic abnormalities in this syndrome are similar to those seen in autosomal recessive polycystic kidney disease consisting of ductular dysgenesis, intrahepatic cysts and portal fibrosis. The incidences of reported hepatic abnormalities range from 33% to 100%. The presence of a central nervous system abnormality helps differentiate this syndrome from other purely isolated severe renal malformations. Most commonly an occipital encephalocele is seen. As an encephalocele can often be seen quite readily using endovaginal ultrasound in early pregnancy it may be the first clue that the syndrome is present in early gestation. Due to the associated oligohydramnios, the cranial abnormalities may be more readily seen than the abdominal, renal abnormalities. Recently, several reports of Meckel's syndrome have appeared in the literature in which the CNS abnormality was Dandy-Walker malformation.

Early Meckel-Gruber Syndrome

Cystic-dysplastic kidneys filling the fetal abdomen

Severe oligohydramnios with an occipital encephalocele

Early 2nd trimester pregnancy with enlarged cystic kidneys

In a recent review of this syndrome, Summers et al reported a case of Dandy-Walker malformation and summarized the expression of this disease in siblings. In their report they stated that half of families with more than one affected Meckel's syndrome individual may have different manifestations of the syndrome in subsequent offsping. In a series by Fraser et al, the only common anomaly was cystic dysplasia of the kidneys, 63% had an occipital encephalocele, 55% had polydactyly and 18% had no evidence of a CNS anomaly. In families in which one offspring had the classic triad, only 68% of subsequent affected siblings also had all three defects.

As stated above, the sonographic recognition of this syndrome is important for two major reasons: 1) it is a uninformly fatal syndrome and 2) parents can be counseled appropriately about the subsequent risk being 25% rather than 1-3%, commonly stated for recurrent malformations.

References:

Pardes JG, Engel IA, Blomquist K, Magid MS, Kazam E. Ultrasonography of intrauterine Meckel's syndrome. J Ultrasound Med 3:33-35, 1984

Nyberg DA, Hallesy D, Mahony BS, Hirsch JH, Luthy DA, Hickok D. Meckel-Gruber syndrom: importance of diagnosis. J Ultrasound Med 9:691-696, 1990

Herriot R, Hallan LA, Gray ES. Dandy-Walker malformation in the Meckel syndrome Am J Med Genetics 39:207, 1991

Wright C et al. Meckel syndrome: what are the minimum diagnostic criteria? J Med Genetics 31:482, 1994

Summers MC, Donnenfeld AE. Dandy-Walker malformation in the Meckel syndrome. Am J Med Genetics 55:57-61, 1995

Fraser FC, Lytwyn A. Spectrum of anomalies in the Meckel syndrome or : maybe there is a malformation sydnrome with at least one constant anomaly. Am J Med Genetics 9:63-73, 1981

Blankenberg TA, Ruebner BH, Ellis WG, Bernstein J, Dimmick JE. Pathology of renal and hepatic anomalies in Meckel syndrome. Am J Med Genet Suppl 3:395-410, 1987

Salonen R. The Meckel syndrome:clinicopathologic findings in 87 patients. Am J Med Genetics 18:671-689, 1984

Sepulveda W, Sebire NJ, Souka A, Snijders JM, Nicolaides KH. Diagnosis of the Meckel-Gruber syndrome at eleven to fourteen weeks' gestation. Am J Obstet Gynecol 176:316-319, 1997

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Peter W. Callen, M.D.
Professor of Radiology, Obstetrics, Gynecology and Reproductive Science
University of California Medical Center, San Francisco, California