Perisylvian syndrome is a rare neurological disease characterized by damage to the sylvian fissure (lateral sulcus), an area in the brain involved in language and speech. The main symptoms are difficulty chewing and swallowing, low muscle tone in the face and tongue, speech and language development disorders, and epilepsy. These symptoms are also often accompanied by difficulties with mobility and intellectual disabilities. The history evidence and exact underlying cause of this condition has not been sourced by researchers and other experts. Due to its low prevalence and possible misdiagnosis, there is a lack of definitive information. Many articles postulate several sources for causes, such as stroke and external trauma to the head, causing damage to the fissure and resulting in malfunctioning structures that interact with it. Other articles have included explorations in diagnosis and treatment of symptoms, with some exploratory treatment of the fissure damage. The fissure has become a subject of increasing focus due to the significant anatomical structures that cross it. It is not to be confused with congenital bilateral perisylvian syndrome (CBPS), which is a form of PS that occurs in embryo and appears in birth and childhood
Signs and symptoms Due to the relationships the fissure has with multiple vital parts of the brain, damage to any one of them can alter the function of the adjacent cortical regions, disrupting the connection between the cognitive, neural, and muscular networks. It is unclear if these are long-term or short term in duration, but symptoms are implied to be permanent without medical intervention.
Speech Trauma to the fissure near the temporal lobe can cause speech issues. Wernicke's area is located on the superior temporal gyrus next to the end of the Sylvian fissure that sits towards the back of the head. This area is part of the language system, and has a major function in the ability to recall speech sounds associated with written letters. Damage to this area can cause anomia, a language disorder that makes it difficult to locate words, and phonemic paraphasia. The sylvian surface on the frontal lobe (located deep in the sylvian fissure) contains a bundle of fibers called the arcuate fasciculus (AF) that curve around the fissure, and comes from Broca's area, which is involved in language production and comprehension. Damage to this nerve bundle can cause conditions such as Broca's aphasia and expressive aphasia.
Auditory processing disorders Damage to the fissure near the temporal lobe may also cause auditory processing disorders due to the disruption in the neural pathway in the area of the temporal lobe the fissure sits in.
Epilepsy Epilepsy is common in studies related to congenital (pre-birth), bilateral (both sides), and unilateral (one side) Perisylvian syndrome. Kuzniecky et al. reported 90% of Perisylvian syndrome cases with epilepsy.
Facial paralysis While the Sylvian fissure does not directly connect to the cranial nerves, previous exploratory dissection reveals that the middle cerebral artery (specifically the M2 segment) runs through the deep insular tissue. Damage to the Sylvian tissue may cause damage or malfunction to the arterial supply of the M2 branch and create an infarction resulting in hemiparesis (unilateral paralysis). A study by Mavili E et al. found that 89% of patients presented with psychomotor retardation, 84% with speech disorders, and 57% with cerebral palsy.
Cause and prevention There are not many definitive pre-occurring conditions and risk factors that lead to the following causes of Perisylvian syndrome. Though the definitive cause is still being explored, it has been well established that the condition cannot be spread from person to person. One study proposes several of the following causes that may create trauma to the fissure:
Cerebral hypoperfusion – a condition where there is inadequate blood flow to the brain, which can be caused by smoking, blood pressure disorders, stroke, and sepsis Stroke – a condition where blood flow to the brain is disrupted, causing brain cells to die off Possible injury during neuronal migration in fetal development (See: congenital bilateral perisylvian syndrome) Brain lesions – an area of damaged brain tissues from injury or disease Other studies have also explored its link to genetics. In the majority of cases, however, the condition appears sporadically.
Cysts Arachnoid cysts represent <1% of intracranial lesions, with the Sylvian fissure being the most common location, most predominant in males on the left side. Cysts are often discovered incidentally during imaging, and most common associated symptoms are headaches, seizures, and motor deficit due to the pressure the cyst applies to the temporal lobe.
Pathophysiology and mechanism The Sylvian fissure is the most prominent crease on the brain. It sits on the lateral hemisphere of the brain, separating the temporal and frontal lobe. It extends into the parietal lobe, and sits perpendicular to the central sulcus, a prominent groove on top of the brain. It also sits in the insula, a part of the brain involved in various functions such as decision making, social emotions, empathy, pain processing, interception, auditory processing. The site is also closely associated with a major cranial artery known as the middle cerebral artery, a vital and the largest branch of the internal carotid artery that is responsible for blood supply to the brain's frontal, temporal, and parietal lobes. It is made up of four branches that extend throughout the brain tissue, labeled as M1, M2, M3, and M4. In most cases of Perisylvian syndrome, the condition exists congenitally and is not typically developed throughout one's lifetime without some sort of significant trauma to the head, causing lesions, pressure, or tissue death, and trickles down to the rest of neural processing in other vital functions of the brain. Once neural processes weaken in these areas, the brain is not able to send signals to its respective parts of the body.
Diagnosis A neurologist would be seen if a diagnosis is desired. Considering the symptoms, a diagnosis may be suggested with visual evidence of the following:
CT scan Early signs of the middle cerebral artery occlusion (MCA) can be found upon discovery of a hyperdense MCA on a brain CT scan. It appears with increased amplitude of the M1 segment, or with increased density in the MCA and branches inside the Sylvian fissure.
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