Carlos Ballario, Hernán Gómez and Maria Eugenia Ferri
Anatomical and functional considerations
The cerebellum is located at the back and bottom of the skull base, behind the fourth ventricle. It is a voluminous nerve mass that weighs 140 g, is ovoid in shape, slightly flattened and with a central notch.
In the midline there is a longitudinal eminence called the vermis, and on each side of the vermis there are two voluminous eminences called the cerebellar hemispheres. These hemispheres are covered by a thin layer of gray matter, folded in numerous convolutions.
The cerebellum communicates with the brain through cords of fibers called superior peduncles, with the annular bulge through the middle peduncles, and with the medulla oblongata through the lower peduncles.
It is mainly a motor organ and is responsible for the regulation and control of muscle tone, the coordination of movements, especially of the volunteers, and the control of posture and gait.
This body is subdivided into three parts:
Flocculonodular lobe or archicerebellum: it is in intimate contact with the vestibular connections and is responsible for regulating balance.
Anterior lobe or paleocerebellum: it is made up of the upper vermix and the adjacent paravermian cortex. It is responsible for receiving proprioceptive input from muscles and tendons.
Posterior lobe or neocerebellum: it is formed by the middle portion of the vermis and by the cerebellar hemispheres. Its activity is very broad, participating in the regulation of different functions of this organ and in connection with many other areas of the central nervous system.
Symptoms and signs
Cerebellar dysfunction can manifest itself in different ways:
1- Hypotonia: it is characterized by a decreased resistance to palpation or passive manipulation of the muscles. In general, it is accompanied by diminished osteotendinous reflexes of the pendulum type, together with a rebound phenomenon in the Steward-Holmes test (it consists of the examiner asking the patient to flex his arm with force activating his biceps muscle against a resistance that The examiner himself opposes. Suddenly the examiner suspends the resistance and the patient's limb does not slow down as usual due to normal reflex activity, but hits against his own body).
2- Ataxia: it is the alteration of the coordination of voluntary movements. It can manifest itself in the limbs (limb ataxia), in the trunk (trunk ataxia), in the cervicocephalic portion (cephalic ataxia) or in gait (gait ataxia).
3- Dysmetria: it is the inability to calculate the distance of the movements. It can present as hypermetry when the movement is exaggerated or as hypometry when the movement is shorter than normal. It is explored with the index-nose and heel-knee tests.
4- Adiadochokinesia: it is the inability to perform rapid and coordinated alternating movements.
5- Tremor: it is an action tremor that manifests itself either in the intention (more important at the end of the movement) or in the attitude (for example, when holding the upper limbs extended forward).
6- Gait alteration: it is an unstable gait, with an increase in the base of support. Also called the drunkard's march.
7- Dysarthria: it is a dragged, explosive, scanned word.
8- Nystagmus: it is generally pluridirectional.
Causes of cerebellar syndromes
Vascular : ischemic and hemorrhagic stroke.
Inflammatory : infectious and post-infectious cerebellitis, multiple sclerosis, abscesses.
Degenerative : Friedrich's ataxia and other spinocerebellar degenerations, paraneoplastic or alcoholic cerebellar degeneration, chronic deficiency of certain vitamins (B12, E).
Toxic : acute ingestion of alcohol, antiepileptics (especially phenytoin and phenobarbital)
Tumors : both the cerebellum itself and the cerebellopontine angle.
Interrogation and physical examination : they are of fundamental importance to locate the pathology topographically. Both the interrogation and the neurological examination will be aimed at ruling out the cerebellar signs and symptoms described above.
Laboratory : some laboratory alterations can be useful to confirm a vitamin deficiency, an excess of drug in the blood (phenytoin).
Lumbar puncture : indicated only in very specific situations.
Computed tomography : currently its value is limited since the capacity of this method to evaluate the posterior fossa is low. However, it can detect spontaneous or traumatic bleeding early.
Nuclear magnetic resonance : it is the method of choice to evaluate the affections of the cerebellum.
Labyrinthine ataxia : in her the drive and nystagmus are of fixed direction. The patient has frequent falls. Romberg's sign is positive (fall to the side of the injured labyrinth).
Sensitive ataxia : due to deficit of profound sensitivity. The patient has a heels gait, with his gaze fixed on the floor and the Romberg sign is also positive.
Frontal ataxia : it is a "magnetized" gait, that is, with short steps close to the floor.