Posterior Fossa Syndrome- Neurology
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Posterior fossa syndrome (also known as cerebellar mutism syndrome) is a complex and not well understood condition that comes as a possible consequence after removing a common type of tumor in children. It was first described in 1964 by Dr. Hirsh.
Anatomically, the posterior fossa is a small space below the cranium located between the cerebellum and brainstem. If you place your hand on the back of your head just above the point where the neck begins your palm will be aligned with the posterior fossa.
A posterior fossa tumor (PFT) is the name given to a group of solid tumors located in this small space, they are more common in children (50 to 70% of all tumors of the central nervous system), although they can also be present in adults (15 to 20% of all tumors of the CNS).
The posterior fossa syndrome is a series of symptoms that sometimes occur after (and as consequence of) the surgical procedure used to remove PFTs. Of all children treated, between 8 to 24% will develop the condition. Some researchers have even found cases where up to 31% of children experience at least some of the main symptoms.
Without a doubt, the most common and characteristic symptom of the posterior fossa syndrome (PFS) is mutism. Most patients experience partial of complete loss of the ability to speak, this can last from 4 days to 5 months depending of the case.
Other symptoms can include:
- Ataxia (motor problems): Instability while walking and loss of muscular tone
- Behavioral problems: restlessness, psychological regression, poverty of spontaneous movement and withdrawal.
- Changes of mood: Dysphoria, apathy, distress, inconsolability, tearfulness, giggling, distractibility and irritability.
The cause of the posterior fossa syndrome is currently unknown. Many researchers tried to find the exact mechanism behind this phenomenon without much success, however, there are a few valid hypotheses that, although not confirmed, do consider our current knowledge of the PFS.
- Hypothesis 1 (Vasospasm): Vasocontraction of the blood vessels that feed the cerebellum due to the surgical intervention causes poor blood supply (ischemia), leading to injury and the development of the main symptoms.
- Hypothesis 2 (Oedema): A common side effect of surgery is fluid retention; this idea suggests that the accumulation causes an injury.
- Hypothesis 3 (Neural injury): The procedure itself causes an injury to nervous tissue which triggers cell death and a meaningful loss of brain tissue.
Although the mechanism is not clear, most researchers agree in that some form of injury over brain structures must be responsible for causing the manifestation of the syndrome.
To date, the most consistent risk factors for posterior fossa syndrome in patients to be treated are:
- Having a tumor located on the Vermis
- Age (younger individuals)
- Having a medulloblastoma
- Cerebellar invasion (the tumor spreads to the cerebellum)
- Complete tumor resection
Other factors like gender, tumor size, infection and meningitis were considered but have been consistently found to have no correlation to PFS.
As medical imaging technology continues to develop, more data can be gathered with procedures like MRI, facilitating the detection of injuries in brains structures after surgery, however, from a simple and clinical standpoint the diagnosis of posterior fossa syndrome is based on 2 criteria:
a) The patient has gone through a posterior fossa tumor resection.
b) After surgery (1 to 3 days) the patient displays reduced capacity for speech or total mutism.
To this day, most of the clinical trials related to treatment of the posterior fossa syndrome have bought almost no benefit for the affected population. An alternative that is still under evaluation if Bromocriptine, a pharmaceutical that has proven to be effective in the treatment of akinetic mutism, but more research needs to be done before reaching any conclusions about its effectiveness for PFS.
Patients often only have the option of managing the main symptoms through physical therapy, occupational therapy, speech therapy and neurocognitive support.
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