Alexia without agraphia following biopsy of a left thalamic tumor

Clinicoradiological Features of Alexia Without Agraphia

Alexia without agraphia is a striking vascular syndrome of the acquired inability to read words just written down. This syndrome occurs after lesions in the splenium of the corpus callosum that disconnect the angular gyrus from the visual pathway. Most of the time, a lesion in the left occipital lobe is also present, and patients present with a visual field deficit. It is a classic neurological syndrome that is rarely seen. We present two cases of alexia without agraphia seen in our hospital the same week.

Myelin Water Imaging Demonstrates Lower Brain Myelination in Children and Adolescents With Poor Reading Ability

Magnetic resonance imaging (MRI) provides a means to non-invasively investigate the neurological links with dyslexia, a learning disability that affects one’s ability to read. Most previous brain MRI studies of dyslexia and reading skill have used structural or diffusion imaging to reveal regional brain abnormalities. However, volumetric and diffusion MRI lack specificity in their interpretation at the microstructural level. Myelin is a critical neural component for brain function and plasticity, and as such, deficits in myelin may impact reading ability. MRI can estimate myelin using myelin water fraction (MWF) imaging, which is based on evaluation of the proportion of short T2 myelin-associated water from multi-exponential T2 relaxation analysis, but has not yet been applied to the study of reading or dyslexia. In this study, MWF MRI, intelligence, and reading assessments were acquired in 20 participants aged 10–18 years with a wide range of reading ability to investigate the relationship between reading ability and myelination. Group comparisons showed markedly lower MWF by 16–69% in poor readers relative to good readers in the left and right thalamus, as well as the left posterior limb of the internal capsule, left/right anterior limb of the internal capsule, left/right centrum semiovale, and splenium of the corpus callosum. MWF over the entire group also correlated positively with three different reading scores in the bilateral thalamus as well as white matter, including the splenium of the corpus callosum, left posterior limb of the internal capsule, left anterior limb of the internal capsule, and left centrum semiovale. MWF imaging from T2 relaxation suggests that myelination, particularly in the bilateral thalamus, splenium, and left hemisphere white matter, plays a role in reading abilities. Myelin water imaging thus provides a potentially valuable in vivo imaging tool for the study of dyslexia and its remediation.

Alexia With and Without Agraphia: An Assessment of Two Classical Syndromes

Background:

Current cognitive models propose that multiple processes are involved in reading and writing.

Objective:

Our goal was to use linguistic analyses to clarify the cognitive dysfunction behind two classic alexic syndromes.

Methods:

We report four experiments on two patients, one with alexia without agraphia following occipitotemporal lesions, and one with alexia with agraphia from a left angular gyral lesion.

Results:

The patient with occipital lesions had trouble discriminating real letters from foils and his reading varied with word-length but not with linguistic variables such as part of speech, word frequency or imageability. He read pseudo-words and words with regular spelling better, indicating preserved use of grapheme-to-phoneme pronunciation rules. His writing showed errors that reflected reliance on ‘phoneme-to-grapheme’ spelling rules. In contrast, the patient with a left angular gyral lesion showed better recognition of letters, words and their meanings. His reading was better for words with high imageability but displayed semantic errors and an inability to use ‘grapheme-to-phoneme’ rules, features consistent with deep dyslexia. His agraphia showed impaired access to both an internal lexicon and ‘phoneme-to-grapheme’ rules.

Conclusion:

Some cases of pure alexia may be a perceptual word-form agnosia, with loss of internal representations of letters and words, while the angular gyral syndrome of alexia with agraphia is a linguistic deep dyslexia. The presence or absence of agraphia does not always distinguish between the two; rather, writing can mirror the reading deficits, being more obvious and profound in the case of an angular gyral syndrome.

Progressive Wallerian Degeneration of the Corpus Callosal Splenium in a Patient with Alexia Without Agraphia: Advanced MR Findings

The corpus callosal splenium is an uncommon location for Wallerian degeneration (WD), which may be mistaken for new pathology on magnetic resonance imaging (MRI). We describe the case of a 69-year-old woman with a left posterior cerebral artery infarct in whom progressive WD of the splenium of the corpus callosum seen on MRI was misinterpreted as new infarction or neoplasm. We address how magnetic resonance spectroscopy, perfusion MRI, diffusion tensor MRI, and serial imaging were utilized in establishing the correct diagnosis. Interestingly, the patient also presented with alexia without agraphia, which has never been reported in association with splenial WD. It is conceivable that WD affected critical splenial association fibers resulting in this uncommon dissociation syndrome.

Brain mechanisms and reading remediation: more questions than answers

Dyslexia is generally diagnosed in childhood and is characterised by poor literacy skills with associated phonological and perceptual problems. Compensated dyslexic readers are adult readers who have a documented history of childhood dyslexia but as adults can read and comprehend written text well. Uncompensated dyslexic readers are adults who similarly have a documented history of reading impairment but remain functionally reading-impaired all their lives. There is little understanding of the neurophysiological basis for how or why some children become compensated, while others do not, and there is little knowledge about neurophysiological changes that occur with remedial programs for reading disability. This paper will review research looking at reading remediation, particularly in the context of the underlying neurophysiology.

Thalamic semantic paralexia

Alexia may be divided into different subtypes, with semantic paralexia being particularly rare. A 57 year old woman with a discreet left thalamic stroke and semantic paralexia is described. Language evalution with the Boston Diagnostic Aphasia Battery confirmed the semantic paralexia (deep alexia). Multimodality magnetic resonance imaging brain scanning excluded other cerebral lesions. A good recovery ensued.

Spelling and reading: using visual sensitivity to explore shared or separate orthographic representations

Do we use the same neurocognitive mechanisms to spell that we do to read? There is a considerable number of conflicting findings, such that evidence has been provided to support common mechanisms for reading and spelling, while other research supports the proposal that reading and spelling utilise unique neurocognitive resources. Sensitivity to visual spatial-frequency doubling (FD) has been demonstrated to correlate with and specifically predict orthographic processing when reading; therefore, if spelling and reading share some elements of orthographic representation, sensitivity to FD should similarly correlate with, and predict, spelling ability by virtue of this shared association. A double dissociation between reading and spelling was found such that sensitivity to the FD task, as mediated by the visual dorsal stream, predicted reading ability but not spelling, while the visual control task predicted spelling but not reading ability, in poor readers/spellers. The results support a dual-orthographic model with separate orthographic representations for reading and spelling.

Corpus callosotomy in children and the disconnection syndromes: a review

OBJECTS

Disconnection syndromes following corpus callosotomy represent complex and variably expressed groupings of signs and symptoms affecting motor control, spatial orientation, vision, hearing, and language. Little is known, however, about the functional topography of callosal fiber pathways. In addition, most published case reports and case series of corpus callosotomy seldom report neurological deficits. We sought to categorize these deficits based on surgical anatomy.

METHODS

We comprehensively reviewed the literature and described, compiled, and tabulated the most common disconnection syndromes complicating corpus callosotomy. We depict the topography of the cerebral cortex and associated commissural fibers of the corpus callosum through illustrations and diffusion tensor imaging tractography.

CONCLUSIONS

Anatomical classification of disconnection syndromes will provide great value to neurosurgeons embarking on callosotomy, whether partial or complete. Such information will apply to procedures performed for epilepsy and to procedures where the corpus callosum is sectioned for access to lesions within the ventricular system.