Structural brain abnormalities

What are the structures of the brain and what do they do?

The brain acts as the control center of the central nervous system, which consists of the brain and spinal cord. The brain regulates many bodily functions including movement, thought, speech, vision, respiration, planning, emotions, and memory by receiving and analyzing sensory input (information) from the body and external environment. It then sends out signals to control and communicate with other regions of the brain and body. PHACE syndrome has been associated with abnormalities of several different areas of the brain. One area in particular is the space at the base of the skull which contains the brain stem and cerebellum, called the posterior fossa.

• Hindbrain
  This is an area of the brain that includes the cerebellum, medulla oblongata and pons. This brain region plays a central role in the execution of involuntary or autonomic behaviors (actions you do not need to think about doing, such as blinking and temperature regulation).
  • Spinal Cord
    Think of this as the main highway system that provides a link between the brain and the body, carrying information back and forth between the two.
  • Medulla Oblongata
    The area of the brain that helps to control autonomic (involuntary) functions such as breathing, digestion, and heart rate.
  • Pons
    The area of the brain that plays an important role in consciousness and sleep.
  • Cerebellum
    Traditionally viewed as the area of the brain which controls complex motor functions. It also plays a key role in selecting the appropriate behavior or action in a given situation (like choosing the correct sequence of movements when reaching for a cup, or selecting the appropriate emotional or social response at a funeral versus a birthday). Additionally, the cerebellum plays a role in the more complex features of human language (such as determining how two words are related, or deciding if a sentence is grammatically correct). Finally, the ability of the cerebellum to change behavior in response to rapid changes or cues is an important feature of executive functions like planning, reasoning, working memory and verbal fluency.

Figure 6: Major structures of the brain associated with PHACE syndrome

• Cerebral cortex
  This is what most people think of when describing the brain. The cerebral cortex is divided into two hemispheres (halves), the right and left. The right hemisphere controls the left side of the body and vice versa.
  • Frontal lobe
    Located at the front of the brain, this is the area of the brain associated with complex reasoning, planning, behavior regulation, personality, decision making, movement and expressive language abilities.
  • Parietal lobe: This area of the brain plays a key role in the processing of sensation (pain and touch), orientation to objects in our environment, movement, speech and visuospatial perception.
  • Temporal lobe
    The area of the brain associated with auditory (sound) processing, emotion, memory, language organization and comprehension (understanding) and retrieval of information from memory storage.
  • Occipital lobe
    Located at the back of the brain, this area controls the processing, integration and interpretation of visual information.

What structural brain abnormalities are seen in children with PHACE syndrome?

• Dandy-Walker complex is a developmental malformation of the brain involving the cerebellum and the fluid-filled spaces around it. It includes an enlargement of the fourth ventricle (a small channel that allows fluid to flow freely between the upper and lower areas of the brain and spinal cord), a partial or complete absence of the area of the brain between the two cerebellar hemispheres (cerebellar vermis) and cyst formation near the internal base of the skull. Hydrocephalus (an enlargement of the fluid-filled spaces surrounding the brain which may lead to increased pressure inside the skull and increased head size) may also be present.
• Cerebellar hypoplasia or atrophy is a neurological condition in which the cerebellum is not fully developed or is smaller than usual. The terms hypoplasia, atrophy and dysgenesis are often used interchangeably. In patients with PHACE syndrome, the hypoplasia is usually only in one half of the cerebellum.
• Subependymal and arachnoid cysts are found in the brain as sacs of cerebrospinal fluid surrounded by a membrane.
• Hypoplasia or agenesis of cerebrum is a developmental abnormality characterized by the absence or reduced size of a cerebral hemisphere. This abnormality may be related to a stroke occurring during fetal development.
• Hypoplasia or agenesis of the corpus callosum is a developmental abnormality in which there is a partial or complete absence of the corpus callosum (a structure that connects the left and right sides of the brain). This defect can occur alone or in combination with other brain defects such as Dandy-Walker complex.
• Hypoplasia or agenesis of the septum pellucidum is a developmental abnormality in which the septum pellucidum (a thin membrane found in the middle of the brain) is absent or reduced in size.
• Hypoplasia or agenesis of the vermis is a developmental abnormality characterized by a partial or complete absence of the cerebellar vermis (the middle portion of the cerebellum located between the two cerebellar hemispheres which plays a role in the body's position control). This abnormality often occurs as a component of the Dandy-Walker complex.
• Polymicrogyria is characterized by a greater than normal amount of folding (gyri) of the surface of the cerebral hemispheres.
• Cortical dysplasia occurs when neurons (nerve cells) do not migrate to the proper location on the cerebral cortex (outermost layer of the cerebrum).
• Absent pituitary or partially empty sella turcica. The pituitary is a small endocrine gland (see Endocrine Abnormalities section) located at the base of the brain. It produces several hormones which are important in controlling growth, thyroid function, salt and water balance in the body and sex hormones. The sella turcica is a bony structure in the base of the skull which holds the pituitary gland. The pituitary gland can be underdeveloped or completely absent in children with PHACE syndrome.

How common are structural brain abnormalities in PHACE syndrome?

Recent studies have reported that 35-52 percent of children with PHACE syndrome have a structural brain malformation. Patients with structural malformations almost always have at least one associated abnormality of the cerebral vasculature (blood vessels of the brain). Cerebellar hypoplasia is the most common structural brain malformation in children with PHACE syndrome.

What are some of the complications involved with having structural brain abnormalities?

Generally, cerebellar abnormalities are shown by having symptoms of hypotonia (see Neurologic Abnormalities section), disequilibrium (loss of balance during activities such as walking or sitting), and dyssynergia (loss of more complex coordinated motor activities). Dyssynergia can result in a variety of symptoms including slurred speech, difficulty coordinating voluntary movements, difficulty stopping a movement once it has started, difficulty in performing rapidly alternating movements, and lack of coordinated eye movements.

In addition to these motor symptoms, structural brain abnormalities of the cerebellum in particular can result in many neuropsychological symptoms (see Neurologic Abnormalities section).

What tests may be needed to diagnose structural brain abnormalities?

Brain abnormalities cannot be diagnosed by a physical exam, so an MRI or computed tomography (CT) is used to diagnose structural brain abnormalities.

What specialists may be involved in a child's care for brain anomalies?

Children with neurologic components of PHACE syndrome may have a care team including a neurosurgeon, neurologist, neuroradiologist, dermatologist, physical therapist, occupational therapist, speech therapist and other medical professionals.

Useful resources for parents and families:

National Institute of Neurological Disorders and Stroke: http://www.ninds.nih.gov

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