Submicrocephaly, also known as Chiari malformation, is a congenital developmental anomaly. It is often associated with compression of adjacent cranial and cervical nerves, hydrocephalus and spinal cord cavity formation. The onset of the disease is slow, with more females than males; the age ranges from 13 to 68 years, with an average of 38 years.
Mild subcerebellar tonsillar herniation may be asymptomatic, but trauma, infection, cough and lumbar puncture may induce symptoms or aggravate them. Symptoms caused by subcerebellar tonsillar herniation include the following.
Posterior group cerebral nerve symptoms
The symptoms include difficulty in swallowing, hoarseness, dull or absent gag reflex, etc.
Symptoms of cervical nerve involvement
Occipital and cervical pain, tonicity, and limitation of movement. Unilateral or bilateral upper limb numbness, weakness, muscle atrophy, etc.
Medulla oblongata and upper cervical medulla symptoms
Motor impairment of limbs, hemiparesis, even quadriplegia, sensory impairment of limbs, hyperactive tendon reflexes, presence of pathological reflexes, urinary and fecal disorders.
Cerebellar symptoms
Slurred speech, unstable walking, nystagmus.
Increased intracranial pressure
manifested as headache, nausea, vomiting and optic papillary edema.
Spinal cord cavity formation
Sensory abnormalities, hyperalgesia or loss of pain and temperature sensation, muscle atrophy of both upper limbs, weakness, and muscle atrophy of both hands in the form of “claw-shaped hands”.
Clinical staging is divided into 3 types according to the severity of the lesion.
Type I is the mildest type. It is characterized by herniation of the cerebellar tonsils downward through the foramen magnum into the spinal canal, mild downward displacement of the medulla oblongata, and normal position of the fourth ventricle.
Type II is the most common type. It is characterized by herniation of the cerebellar tonsils with or without earthworms into the spinal canal, elongation and downward displacement of the fourth ventricle, underdevelopment of certain structures such as the skull, dura mater, and cerebellum, and hydrocephalus in 90% of cases, often combined with spinal cord cavitation, abnormal neuronal migration, and spinal cord spinal membrane expansion.
Type III is the most severe type and is rare. It shows herniation of the medulla oblongata, cerebellar earth, four ventricles and part of the cerebellar hemispheres into the upper part of the vertebral canal, combined with occipital meningeal brain expansion, and obvious head and neck deformity, cerebellar malformation, etc.
Diagnostic criteria
MRI, with its high soft tissue resolution, can clearly show the exact location of the subungual herniation of the cerebellum and the presence or absence of the medulla oblongata and subventricular herniation of the fourth ventricle without the injection of any contrast agent.