Case 7: Hydranencephaly

HISTORY

A 22-year-old pregnant woman, gravida 4 para 3 (with three normal children) presented at 34 gestational weeks for her first prenatal care visit. Ultrasonographic (US) images showed an enlarged head in a single, live fetus (Fig 1).

One month later, the woman was delivered of a 4,870 g (10 lb 7 oz) boy by means of cesarean section. The newborn had a head circumference of 42 cm (normal = 34.5 cm). Computed tomography (CT) of the newborn's head was performed on day 2 (Fig 2).

IMAGING FINDINGS

US scans (Fig 1) of the enlarged fetal head demonstrated a discontinuous falx midline echo and no identifiable cortical mantel. Normal hyperechoic choroid plexuses were seen posterior to normal thalami, and a small amount of occipital cortex remained, posterior to both. The midbrain was preserved and an image of the posterior fossa demonstrated an intact cerebellum and a normal cisterna magna.

Two days after delivery, CT of the newborn's head was performed without intravenous contrast material (Fig 2). A disrupted falx was noted. No normal cortical mantle except some occipital cortex could be identified. At the level of the normal thalami, normal choroid plexuses were seen posteriorly. The posterior fossa including the cerebellum was normal.

DISCUSSION

Hydranencephaly is a rare, isolated abnormality occurring in less than 1 per 10,000 births worldwide (1–3). It is the most severe form of bilateral cerebral cortical destruction. The differential diagnosis includes bilaterally symmetric schizencephaly (a less severe destructive process), severe hydrocephalus, and alobar holoprosencephaly (a developmental anomaly).

Hydranencephaly occurs after the brain and ventricles have fully formed, usually in the second trimester. The brain destruction is complete or almost complete in a bilateral internal carotid artery distribution, with the cerebral hemispheres replaced by fluid covered with leptomeninges and dura. During the destructive phase, unusual “masses” of hemorrhage and soft tissue may be seen (4). Because the ventricles have already been formed, the falx cerebri is present. The cerebellum, midbrain, thalami, basal ganglia, choroid plexus, and portions of the occipital lobes, all fed by the posterior circulation, are typically preserved.

With most of the cerebral cortex absent, the fetal head would be expected to be small. Although this may occur, the head is more often normal or increased in size because the choroid plexuses within the lateral ventricles continue to produce cerebral spinal fluid that is not adequately absorbed. This causes increased pressure, which may expand the head and lead to rupture of the falx cerebri. Both of these findings were present in this case.

While the pathogenesis of hydranencephaly is thought to be a vascular accident, this cannot always be confirmed because internal carotid arteries are not always occluded at autopsy (1). Intrauterine infections, particularly toxoplasmosis and viral infections (enterovirus, adenovirus, parvovirus, cytomegalic, herpes simplex, Epstein-Barr, and respiratory syncytial viruses), have been implicated in a number of cases. Toxic exposures and cocaine abuse have been reported, and hydranencephaly has been described in rare syndromes (5). In monochorionic twin pregnancies, death of one twin in the second trimester may cause a vascular exchange to the living twin through the placental circulation, leading to hydranencephaly in the surviving fetus (6).

Hydranencephaly may, on first impression, mimic severe hydrocephalus (dilated lateral ventricles)(2). Depending on the level of obstruction, concomitant dilatation of the third and fourth ventricles may be seen. The incidence of hydrocephalus approaches 1 in 1,000 births. Although there are many causes, the most common is an Arnold-Chiari type II malformation secondary to a spina bifida. The most severe cases, however, are usually secondary to aqueductal stenosis. Hydrocephalus is often not an isolated anomaly and can be associated with other intracranial abnormalities, multiple anomaly syndromes, and abnormal karyotype (7).

With hydrocephalus, as with hydranencephaly, the head is normal to enlarged with an identifiable falx cerebri, which may be disrupted in severe cases. Unlike in hydranencephaly, an intact rim of cortex is always present even in the most severe forms of hydrocephalus (Fig 3). It may, however, be difficult to identify prenatally. In aqueductal stenosis, a dilated third ventricle can often also be identified.

A porencephalic cyst is a focal area of cortical destruction (1,2). When caused by middle cerebral artery infarctions, porencephalic cysts appear as bilateral fluid-filled clefts that communicate with the ventricles and is called schizencephaly. Unlike in hydranencephaly, both the frontal and parieto-occipital cortex are preserved. The falx cerebri is also preserved. Abnormal brain growth and development may result, depending on the timing of the occlusions. The fetal head can be either normal or enlarged.

Holoprosencephaly is a developmental anomaly resulting from absent or incomplete diverticulation of the forebrain (prosencephalon) and occurs in 1 in 16,000 live births worldwide. Alobar, its most severe form, shows no separation of the ventricles, an absent falx, and partial fusion of the thalami (Fig 4). The head is often considerably smaller than the body, and there are often additional and marked abnormalities.

There are important reasons to differentiate hydranencephaly from hydrocephalus; these reasons relate to prognosis and management (8,9). Children with hydrocephalus, without chromosomal or other structural abnormalities, have an unpredictable prognosis. With proper ventricular shunt after birth, mentation may in some cases be normal. In contradistinction, hydranencephaly has an irretrievably poor prognosis, with only brain stem function remaining. Although most hydranencephalic children survive birth, they often die soon after. Rarely, these children may linger into their teenage years. If the fetal head is enlarged, the differentiation of hydranencephaly from hydrocephaly has added importance because an enlarged head may not be able to be delivered vaginally. If hydranencephaly were definitively diagnosed in utero, cephalocentesis could be offered to decompress the fetal head, thus allowing a vaginal delivery. While this may damage the fetal head further, it will not change the outcome and will importantly spare the mother an unnecessary operation. On the other hand, if hydrocephalus were present, particularly without the presence of other anomalies, a cesarean section must be seriously considered.

Our congratulations to the 139 individuals who submitted the most likely diagnosis (hydranencephaly) for Diagnosis Please, Case 7. Their names and locations, as submitted, are as follows:

Gholamali Afshang, MD, Tinley Park, Ill

S. I. Al-Agha, MD, Gaza, Israel

S. Manucher Alavi, MD, Richmond, Va

David R. Anderson, MD, Richmond, Va

Roger L. Antonelli, MD, Dayton, Ohio

Majed Ashour, MD, Dhahran, Saudi Arabia

A. Rhett Austin, MD, Kingsport, Tenn

Edward L. Baker, MD, San Francisco, Calif

Kenneth Baliga, Rockford, Ill

Zubin N. Balsara, MD, Fort Smith, Ark

Cynthia A. Barone, DO, Shrewsbury, NJ

John Bennett, MDCM, FRCPC, London, Ontario, Canada

Steven L. Bezinque, DO, Williamsville, NY

Tom Bonk, MD, Seattle, Wash

Nikos P. Bontozoglou, MD, Athens, Greece

Eric L. Bressler, MD, Minnetonka, Minn

Steve Burbidge, MD, St Louis Park, Minn

Joseph W. Burke, MD, Huntingdon, Pa

Can Cevikol, Antalya, Turkey

Ercument Ciftci, MD, Houston, Tex

Frederick U. Conard III, MD, Hartford, Conn

Philippe A. Coquel, MD, Cran-Gevrier, France

Mark T. DiMarcangelo, DO, MSc, Cherry Hill, NJ

Vinay Duddalwar, Aberdeen, United Kingdom

Peter English, FRACR, Hong Kong, China

Keith D. Epperson, MD, Milwaukee, Wis

Kate A. Feinstein, MD, Chicago, Ill

Laura Zindell Fenton, MD, Denver, Colo

Sylvia H. Ford, MD, Green Bay, Wis

Jonathan Foss, MD, St Louis, Mo

Michael A. Foster, MD, Cherry Hills Village, Colo

Mary C. Frates, MD, Boston, Mass

Jeffrey Friedland, Glendale, Colo

Arnold C. Friedman, MD, New York, NY

Stuart A. Fruman, MD, Vienna, Va

Akira Fujikawa, Tokyo, Japan

Douglas Gardner, MD, Windsor, Ontario, Canada

Ronald B. J. Glass, MD, New York, NY

Ishikawa Goemon, Shiga, Japan

Jacob A. Goldenberg, MD, Fargo, ND

Dulce Gomez-Santos, MD, Madrid, Spain

Devang Gor, DMRD, Costa Mesa, Calif

Daniel S. Gordon MD, MAJ USA MC, Sanford, NC

Dr. Rajesh Gothi, New Delhi, India

Athanassios D. Gouliamos, Athens, Greece

D. Joseph Grunz, MD, Creve Coeur, Mo

Mark Guelfguat, Flushing, NY

Dr Arunima Gupta, Ludhiana, India

Sunita Gupta, MD, Francistown, Botswana

David C. Harrison, MD, Cambridge, Mass

Rufus W. Head, MD, North Bridgton, Me

Maureen Heldmann, MD, Shreveport, La

Elizabeth Hingsbergen, MD, Richmond, Va

Carlos Holguera Blazquez, MD, Madrid, Spain

Lowrey H. Holthaus, MD, Richmond, Va

Kamil Karaali, Antalya, Turkey

Aake Karlsson Douglas S. Katz, MD, Mineola, NY

Ji Chang Kim, MD, Taejon, Korea

Mitchell Klein, MD, Milwaukee, Wis

Arlene M. Klink, MD, Bronx, NY

John D. Knudtson, MD, Wichita, Kan

Craig D. Korbin, MD, Weston, Mass

Dawna J Kramer, MD, Seattle, Wash

Dr. Renee G. Kulkarni, New Delhi, India

Yu-Ting Kuo, MD, Taiwan, ROC

Dong Lin Kwak, MD, Roanoke, Va

Kathleen M. Lazzarini, MD, Branford, Conn

Jong Beum Lee, MD, Seoul, Korea

Ronaldo Lessa, Jr, MD, Recife, Brazil

Julio Loureiro, MD, Buenos Aires, Argentina

David R. Ludwig, MD, Amherst, NY

António José Madureira, MD, Porto, Portugal

Gildo Matta, MD, Cagliari, Italy

James M. McAfee, MD, West Linn, Ore

Jeffrey J. McClure, MD, Grand Rapids, Mich

Steven Medwid, MD, Fall River, Mass

Edward Menges, MD, Aptos, Calif

Frank H. Miller, MD, Chicago, Ill

Manabu Minami, MD, Tokyo, Japan

Hidetoshi Miyake, MD, Oita, Japan

Sergio J. Moguillansky, MD, Rio Negro, Argentina

Silvia Moguillansky, Buenos Aires, Argentina

Eduardo Mondello, Buenos Aires, Argentina

Albert Nizzero, MD, Sudbury, Ontario, Canada

Aksel Ongre, Arendal, Norway

Mahesh R. Patel, MD, Brookline, Mass

Narendrakumar Patel, MD, Newburgh, NY

Eduardo Pavon Tinoco MD, Oaxaca, Mexico

Tim L. Pendergrass, MD, Fairchild AFB, Wash

Dr Roberto E. Perez Gautrin, Sonora, Mexico

Marvin W. Petry, MD, Chicago, Ill

Pedro J. S. Pinto, MD, Gondomar, Portugal

John Plotke, MD, Naperville, Ill

Gary Podolny, MD, Park City, Utah

Carlos H. Previgliano, MD, Salta, Argentina

Anita Price, MD, Mineola, NY

Shawn P. Quillin, MD, Charlotte, NC

M. R. Ramakrishnan, MD, Big Stone Gap, Va

Oswaldo A. Ramos, MD, Estado Trujillo, Venezuela

Lorenz (Larry) Ramseyer, MD, Enid, Okla

Enrique Remartinez Escobar, Melilla, Spain

Marco A. Rocha Mello, MD, Sao Paulo, Brazil

Javier Rodriguez Lucero, MD, Santa Fe, Argentina

Derek J. Roebuck, FRACR, Hong Kong, China

Stuart A. Royal, MD, Birmingham, Ala

Dr Eduardo Sanchez Heras Paul S. Schaefer, MD Steven M. Schultz, MD, Fort Worth, Tex

Anthony J. Scuderi, MD Hassan Semaan, Toledo, Ohio

A. Utku Senol, Antalya, Turkey

Waldo Sepulveda, MD, Santiago, Chile

Matt Shapiro, MD, Boxborough, Mass

Yoshihisa Shimanuki, MD, Yamagata, Japan

L.H. Sie, MD, Beverwijk, the Netherlands

James F. Smith, Columbia, Mo

Eric R. Sover, DO, Brookfield, Wis

Joanne B. Speigle, MD, Richmond, Va

Michael S. Stecker, MD, Iowa City, Iowa

Marius Stellmann, MD, Rotenburg, Germany

Simon Strauss, MBChB, Kfar Shmaryahu, Israel

Jeffrey Y. Sue, MD, Honolulu, Hawaii

Christopher Sweet, MD, Clarkston, Mich

Koyama Takashi, Kyoto, Japan

J. Takasugi, Mercer Island, Wash

Oscar Tenreiro Picon, MD, Maracay, Venezuela

J. Keith Thompson, MD, Richmond, Va

Joseph Z. H. Toutounji, MD, Beirut, Lebanon

Carlos Triana Rodriguez, Santefe de Bogota, Colombia

Herminia Tyminski, MD, Manama, Bahrain

T. E. G. van Zanten, MD, Haarlem, the Netherlands

Andrew L. Wagner, MD, Durham, NC

Chien-Kuo Wang, MD, Taiwan, ROC

Edward W. Williams, FRCR, Cayman Islands, British West Indies

Joseph T. Wroblicka, MD, Iowa City, Iowa

Masanobu Yasuda, MD, Kanagawa, Japan

Dr. Zhang Youbin, Gaborone, Botswana