Rhombencephalosynapsis is a rare genetic brain abnormality of malformation of the

cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cere ...

. The

cerebellar vermis The cerebellar vermis (from Latin ''vermis,'' "worm") is located in the medial, cortico-nuclear zone of the cerebellum, which is in the posterior fossa of the cranium. The primary fissure in the vermis curves ventrolaterally to the superior surf ...

is either absent or only partially formed, and fusion is seen in varying degree between the

cerebellar hemisphere The cerebellum consists of three parts, a median and two lateral, which are continuous with each other, and are substantially the same in structure. The median portion is constricted, and is called the vermis, from its annulated appearance which ...

s, fusion of the middle cerebellar peduncles, and fusion of the dentate nuclei. Findings range from mild truncal ataxia, to severe

cerebral palsy Cerebral palsy (CP) is a group of movement disorders that appear in early childhood. Signs and symptoms vary among people and over time, but include poor coordination, spasticity, stiff muscles, Paresis, weak muscles, and tremors. There may be p ...

. Rhombencephalosynapsis is a constantly found feature of Gomez-Lopez-Hernandez syndrome. One case of which has shown a co-occurrence with

autism-spectrum disorder The autism spectrum, often referred to as just autism or in the context of a professional diagnosis autism spectrum disorder (ASD) or autism spectrum condition (ASC), is a neurodevelopmental condition (or conditions) characterized by difficulti ...

Presentation

Clinical indications range from mild truncal ataxia with unaffected cognitive abilities, to severe

and

intellectual disability Intellectual disability (ID), also known as general learning disability in the United Kingdom and formerly mental retardation, Rosa's Law, Pub. L. 111-256124 Stat. 2643(2010). is a generalized neurodevelopmental disorder characterized by signif ...

Genetics

An association with mutations in the ''MN1''

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

has been reported in cases of atypical rhomboencephalosynapsis.

Pathology

Rhombencephalosynapsis is a rare brain disorder of malformation of the cerebellum that may be detected on

ultrasound Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies fr ...

of the

fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal develo ...

. The vermis is either absent or partially formed. There is dorsal fusion of the cerebellar hemispheres, fusion of the dentate nuclei, and fusion of the middle cerebellar peduncles. The degree of severity of this disorder is associated with the degree of maldevelopment of the cerebellar vermis. Aqueductal stenosis commonly exists with the disorder, as does its often resulting

hydrocephalus Hydrocephalus is a condition in which an accumulation of cerebrospinal fluid (CSF) occurs within the brain. This typically causes increased pressure inside the skull. Older people may have headaches, double vision, poor balance, urinary in ...

. In some cases additional abnormalities may be present, such as

ventriculomegaly Ventriculomegaly is a brain condition that mainly occurs in the fetus when the lateral ventricles become dilated. The most common definition uses a width of the atrium of the lateral ventricle of greater than 10 mm. This occurs in around 1% ...

(enlarged ventricles), and

supratentorial In anatomy, the supratentorial region of the brain is the area located above the tentorium cerebelli. The area of the brain below the tentorium cerebelli is the infratentorial region. The supratentorial region contains the cerebrum, while the infr ...

abnormalities.

Diagnosis

Rhombencephalosynapsis can be detected on imaging of the fetus. It is one of the triad of features characteristic of Gomez-Lopez-Hernandez syndrome (GLHS). When detected, signs of GLHS ought to be looked for on post-natal review. Signs include partial

alopecia Hair loss, also known as alopecia or baldness, refers to a loss of hair from part of the head or body. Typically at least the head is involved. The severity of hair loss can vary from a small area to the entire body. Inflammation or scarr ...

and some facial peculiarities. It is thought that due to the co-occurrence of these two disorders they may have a common etiology. As a feature of GLHS one case study has shown GLHS to co-occur with

autism spectrum disorder The autism spectrum, often referred to as just autism or in the context of a professional diagnosis autism spectrum disorder (ASD) or autism spectrum condition (ASC), is a neurodevelopmental condition (or conditions) characterized by difficulti ...

Epidemiology

As of 2018 only 36 cases have been reported.

History

The first case was reported by Heinrich Obersteiner in 1914.

References

{{Congenital malformations and deformations of nervous system Congenital disorders of nervous system