The left ventral occipito-temporal cortex (LvOT) is thought to be essential for the rapid parallel letter processing that is required for skilled reading. Here we investigate whether rapid written word identification in skilled readers can be supported by neural pathways that do not involve LvOT. Hypotheses were derived from a stroke patient who acquired dyslexia following extensive LvOT damage. The patient followed a reading trajectory typical of that associated with pure alexia, re-gaining the ability to read aloud many words with declining performance as the length of words increased. Using functional MRI and dynamic causal modelling (DCM), we found that, when short (three to five letter) familiar words were read successfully, visual inputs to the patient’s occipital cortex were connected to left motor and premotor regions via activity in a central part of the left superior temporal sulcus (STS). The patient analysis therefore implied a left hemisphere “reading-without-LvOT” pathway that involved STS. We then investigated whether the same reading-without-LvOT pathway could be identified in 29 skilled readers and whether there was inter-subject variability in the degree to which skilled reading engaged LvOT. We found that functional connectivity in the reading-without-LvOT pathway was strongest in individuals who had the weakest functional connectivity in the LvOT pathway. This observation validates the findings of our patient’s case study. Our findings highlight the contribution of a left hemisphere reading pathway that is activated during the rapid identification of short familiar written words, particularly when LvOT is not involved. Preservation and use of this pathway may explain how patients are still able to read short words accurately when LvOT has been damaged.
A 65 year old female was transferred to the Hyperacute Stroke Unit after a routine L5/S1 laminectomy. She suffered a small dural tear. 3 hours post procedure, her GCS dropped to 3. CT scan showed a bi-cerebellar haemorrhage and MRI brain the next day revealed a convexity subarachoid haemorrhage. Imaging was reviewed with neuroradiologists and neurosurgeons. They recognised this as a typical case of post-dural puncture remote cerebellar haemorrhage. In surgical literature there are many cases reported since 1981 of “the Zebra sign”. Patients can become obtunded up to 72 hours after the injury. The mechanism of the haemorrhage is not fully understood. There are no cases reported after a lumbar puncture, which suggests a rapid loss of CSF is required for the pressure shift. Sudden caudal shift of brain with traction of arachnoid matter and venous structures on brain surface during ‘cerebellar sag’ may result in venous bleeding and sometimes infarction. Usually bleeding is bilateral near upper vermis and cerebellar sulci in close proximity to cerebellar draining veins giving rise to the ‘Zebra sign’. Remote cerebellar haemorrhage is an unknown known for a neurologist but with the increased access to stroke services, we are likely to see more cases.
A 65-year-old woman became obtunded following routine laminectomy and was found to have bilateral cerebellar haemorrhage and convexity subarachnoid haemorrhage. We discuss the possible mechanisms of remote cerebellar haemorrhage—cerebellar haemorrhage that develops after spinal or intracranial surgery—giving rise to the ’zebra sign' and the possible mechanism of convexity subarachnoid haemorrhage in this context [corrected].
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