Pure word deafness after resection of a tectal plate glioma with preservation of wave V of brain stem auditory evoked potentials

Situating word deafness within aphasia recovery: A case report

Word deafness is a rare neurological disorder often observed following bilateral damage to superior temporal cortex and canonically defined as an auditory modality-specific deficit in word comprehension. The extent to which word deafness is dissociable from aphasia remains unclear given its heterogeneous presentation, and some have consequently posited that word deafness instead represents a stage in recovery from aphasia, where auditory and linguistic processing are affected to varying degrees and improve at differing rates. Here, we report a case of an individual (Mr. C) with bilateral temporal lobe lesions whose presentation evolved from a severe aphasia to an atypical form of word deafness, where auditory linguistic processing was impaired at the sentence level and beyond. We first reconstructed in detail Mr. C's stroke recovery through medical record review and supplemental interviewing. Then, using behavioral testing and multimodal neuroimaging, we documented a predominant auditory linguistic deficit in sentence and narrative comprehension-with markedly reduced behavioral performance and absent brain activation in the language network in the spoken modality exclusively. In contrast, Mr. C displayed near-unimpaired behavioral performance and robust brain activations in the language network for the linguistic processing of words, irrespective of modality. We argue that these findings not only support the view of word deafness as a stage in aphasia recovery but also further instantiate the important role of left superior temporal cortex in auditory linguistic processing.

The Auditory Agnosias: a Short Review of Neurofunctional Evidence

PURPOSE OF REVIEW

To investigate the neurofunctional correlates of pure auditory agnosia and its varieties (global, verbal, and nonverbal), based on 116 anatomoclinical reports published between 1893 and 2022, with emphasis on hemispheric lateralization, intrahemispheric lesion site, underlying cognitive impairments.

RECENT FINDINGS

Pure auditory agnosia is rare, and observations accumulate slowly. Recent patient reports and neuroimaging studies on neurotypical subjects offer insights into the putative mechanisms underlying auditory agnosia, while challenging traditional accounts. Global auditory agnosia frequently results from bilateral temporal damage. Verbal auditory agnosia strictly correlates with language-dominant hemisphere lesions. Damage involves the auditory pathways, but the critical lesion site is unclear. Both the auditory cortex and associative areas are reasonable candidates, but cases resulting from brainstem damage are on record. The hemispheric correlates of nonverbal auditory input disorders are less clear. They correlate with unilateral damage to either hemisphere, but evidence is scarce. Based on published cases, pure auditory agnosias are neurologically and functionally heterogeneous. Phenotypes are influenced by co-occurring cognitive impairments. Future studies should start from these facts and integrate patient data and studies in neurotypical individuals.

Cortical disorders of speech processing: Pure word deafness and auditory agnosia

Selective disorders of auditory speech processing due to brain lesions are reviewed. Over 120 years after the first anatomic report (Dejerine and Sérieux, 1898), fewer than 80 cumulative cases of generalized auditory agnosia and pure word deafness with documented brain lesions are on record. Most patients (approximately 70%) had vascular lesions. Damage is very frequently bilateral in generalized auditory agnosia, and more frequently unilateral in pure word deafness. In unilateral cases, anatomical disconnection is not a prerequisite, and disorders may be due to functional disconnection. Regardless of whether lesions are unilateral or bilateral, speech processing difficulties emerge in the presence of damage to the superior temporal regions of the language-dominant hemisphere, suggesting that speech input is processed asymmetrically at early stages already. Extant evidence does not allow establishing whether processing asymmetry originates in the primary auditory cortex or in higher associative cortices, nor whether auditory processing in the brainstem is entirely symmetric. Results are consistent with the view that the difficulty in processing auditory input characterized by quick spectral and/or temporal changes is one of the critical dimensions of the disorder. Forthcoming studies should focus on detailed audiologic, neurolinguistic, and neuroanatomic descriptions of each case.

[A case of Wernicke encephalopathy with hypoacusia and MR high intensity of the inferior colliculi that normalized after thiamine administration]

A 61-year-old man was admitted to our institution with progressive hypoacusia, double vision, and lightheadedness. Neurological examination on day 6 of his illness showed severe hypoacusia, mild confusion, ocular motility disorder, truncal ataxia and absence of a deep tendon reflex. MRI fluid-attenuated inversion recovery imaging revealed symmetrical high intensities in the tectum of the midbrain, involving the bilateral inferior colliculi and the bilateral medial thalami, which suggested Wernicke encephalopathy (WE). Thiamine was administered immediately after completion of the MRI, and the patients' hearing and other abnormal neurologic signs improved rapidly within a few days, except for the absence of the deep tendon reflex. Whole blood examination at admission revealed very low levels of vitamin B1. The patient was discharged on day 19, and MRI on day 39 showed the disappearance of the abnormal high intensities involving the bilateral inferior colliculi. The present case indicates that hypoacusia and abnormal MRI signal due to WE might be normalized by administration of thiamine a few days after the onset of symptoms.

Cortical and Subcortical Substrates of Cranial Nerve Function

The pivotal role of cranial nerves in a wholesome life experience cannot be overemphasized. Research has opened new avenues to understand cranial nerve function. Classical concept of strict bilateral cortical control of cranial nerves has given way to concepts of hemispheric dominance and hemispheric lateralization. An astute Neuroradiologist should keep abreast of these concepts and help patients and referring physicians by applying this knowledge in reading images. This chapter provides an overview of cranial nerve function and latest concepts pertaining to their cortical and subcortical control.

Speech processing disorder in neural hearing loss

Deficits in central auditory processing may occur in a variety of clinical conditions including traumatic brain injury, neurodegenerative disease, auditory neuropathy/dyssynchrony syndrome, neurological disorders associated with aging, and aphasia. Deficits in central auditory processing of a more subtle nature have also been studied extensively in neurodevelopmental disorders in children with learning disabilities, ADD, and developmental language disorders. Illustrative cases are reviewed demonstrating the use of an audiological test battery in patients with auditory neuropathy/dyssynchrony syndrome, bilateral lesions to the inferior colliculi, and bilateral lesions to the temporal lobes. Electrophysiological tests of auditory function were utilized to define the locus of dysfunction at neural levels ranging from the auditory nerve, midbrain, and cortical levels.

Medulloblastoma presenting with pure word deafness: report of one case and review of literature

Pure word deafness (PWD) is a rare disorder characterized by impaired verbal comprehension sparing discrimination and recognition of nonverbal sounds with relatively normal spontaneous speech, writing, and reading comprehension. Etiologies of this syndrome are varied, and there are rare reports about brain tumor with PWD in children. We report a case of medulloblastoma presented with PWD in a 7-year-old girl. She visited our outpatient clinic because of English dictation performance deterioration. PWD was diagnosed by the otolaryngologist after examinations. Posterior fossa tumor and obstructive hydrocephalus were shown in the magnetic resonance imaging of the brain. The diagnosis of medulloblastoma was then made by pathology.

Competition and convergence between auditory and cross-modal visual inputs to primary auditory cortical areas

Sensory neocortex is capable of considerable plasticity after sensory deprivation or damage to input pathways, especially early in development. Although plasticity can often be restorative, sometimes novel, ectopic inputs invade the affected cortical area. Invading inputs from other sensory modalities may compromise the original function or even take over, imposing a new function and preventing recovery. Using ferrets whose retinal axons were rerouted into auditory thalamus at birth, we were able to examine the effect of varying the degree of ectopic, cross-modal input on reorganization of developing auditory cortex. In particular, we assayed whether the invading visual inputs and the existing auditory inputs competed for or shared postsynaptic targets and whether the convergence of input modalities would induce multisensory processing. We demonstrate that although the cross-modal inputs create new visual neurons in auditory cortex, some auditory processing remains. The degree of damage to auditory input to the medial geniculate nucleus was directly related to the proportion of visual neurons in auditory cortex, suggesting that the visual and residual auditory inputs compete for cortical territory. Visual neurons were not segregated from auditory neurons but shared target space even on individual target cells, substantially increasing the proportion of multisensory neurons. Thus spatial convergence of visual and auditory input modalities may be sufficient to expand multisensory representations. Together these findings argue that early, patterned visual activity does not drive segregation of visual and auditory afferents and suggest that auditory function might be compromised by converging visual inputs. These results indicate possible ways in which multisensory cortical areas may form during development and evolution. They also suggest that rehabilitative strategies designed to promote recovery of function after sensory deprivation or damage need to take into account that sensory cortex may become substantially more multisensory after alteration of its input during development.

Hearing improvement after resection of a large jugular foramen schwannoma: case report

Although hearing improvement after surgery for small tumors of the cerebellopontine angle has been reported, the mechanism by which surgery leads to the improvement in hearing remains controversial. We report a patient who sought treatment for progressive tinnitus and hearing loss. Magnetic resonance imaging showed a large (5-cm) schwannoma in the cerebellopontine angle. At surgery the lesion was found to originate from rootlets of cranial nerve X at the jugular foramen. The patient underwent gross total resection of the tumor. Immediately after surgery, his hearing improved dramatically. We believe that our patient represents an example of hearing impairment at least in part referable to direct compression of the brainstem. Importantly, the patient's hearing deficit was completely reversible. Some authors claim that surgery to preserve hearing may be contraindicated in patients with speech discrimination scores below 50%. However, when extrinsic brainstem compression may contribute to the cause of such a hearing decrement, postoperative improvement in hearing may be a reasonable expectation.

Inhalational Exposure to Carbonyl Sulfide Produces Altered Brainstem Auditory and Somatosensory-Evoked Potentials in Fischer 344N Rats

Carbonyl sulfide (COS), a chemical listed by the original Clean Air Act, was tested for neurotoxicity by a National Institute of Environmental Health Sciences/National Toxicology Program and U.S. Environmental Protection Agency collaborative investigation. Previous studies demonstrated that COS produced cortical and brainstem lesions and altered auditory neurophysiological responses to click stimuli. This paper reports the results of expanded neurophysiological examinations that were an integral part of the previously published experiments (Morgan et al., 2004, Toxicol. Appl. Pharmacol. 200, 131-145; Sills et al., 2004, Toxicol. Pathol. 32, 1-10). Fisher 334N rats were exposed to 0, 200, 300, or 400 ppm COS for 6 h/day, 5 days/week for 12 weeks, or to 0, 300, or 400 ppm COS for 2 weeks using whole-body inhalation chambers. After treatment, the animals were studied using neurophysiological tests to examine: peripheral nerve function, somatosensory-evoked potentials (SEPs) (tail/hindlimb and facial cortical regions), brainstem auditory-evoked responses (BAERs), and visual flash-evoked potentials (2-week study). Additionally, the animals exposed for 2 weeks were examined using a functional observational battery (FOB) and response modification audiometry (RMA). Peripheral nerve function was not altered for any exposure scenario. Likewise, amplitudes of SEPs recorded from the cerebellum were not altered by treatment with COS. In contrast, amplitudes and latencies of SEPs recorded from cortical areas were altered after 12-week exposure to 400 ppm COS. The SEP waveforms were changed to a greater extent after forelimb stimulation than tail stimulation in the 2-week study. The most consistent findings were decreased amplitudes of BAER peaks associated with brainstem regions after exposure to 400 ppm COS. Additional BAER peaks were affected after 12 weeks, compared to 2 weeks of treatment, indicating that additional regions of the brainstem were damaged with longer exposures. The changes in BAERs were observed in the absence of altered auditory responsiveness in FOB or RMA. This series of experiments demonstrates that COS produces changes in brainstem auditory and cortical somatosensory neurophysiological responses that correlate with previously described histopathological damage.

Auditory agnosia caused by a tectal germinoma

The authors describe a patient with auditory agnosia caused by a tectal germinoma. Despite having normal audiometric tests, the patient failed to recognize words and musical characters. On head MRI, the inferior colliculi were infiltrated by tumor. Neuropsychological tests revealed severe impairment in recognition of environmental sounds and words, defective musical perception, and stop consonant-vowel discrimination. Inferior colliculus may play a role in the analysis of sound properties.

Reversible hearing loss associated with a malignant pineal germ cell tumor. Case report

In patients with pineal tumors, clinical symptoms are due to direct compression of adjacent structures. The most common signs include increased intracranial pressure (80%) caused by obstruction of the sylvian aqueduct, and Parinaud syndrome (50%) caused by direct compression of the superior colliculi. Hearing loss is rare in patients with tumors in this location. The authors report on the case of a 12-year-old boy in whom a malignant pineal germ cell tumor was found together with the unusual occurrence of severe hearing loss due to direct bilateral compression of the inferior colliculi. This condition resolved completely after tumor regression.

Pure word deafness in two patients with subcortical lesions

We report two patients with pure word deafness (PWD) with tumour in the III ventricle region with obstructive hydrocephalus. A diagnosis of PWD was made in these two patients in view of impaired verbal comprehension in the presence of adequate hearing, intact acoustic stapedius reflex and well preserved environmental sound perception. Return of verbal comprehension following the radiation therapy observed is probably due to the reduction of the tumour mass and the release of thalamocortical auditory pathways from its compressive effect. Our findings support the hypothesis of the presence of discrete auditory pathways for mediation of verbal and non-verbal stimuli independently.

Word deafness after resection of a pineal body tumor in the presence of normal wave latencies of the auditory brain stem response

We studied the case of a 48-year-old woman who had resection of a pineal body tumor in terms of postoperative audiological function. Postoperative magnetic resonance imaging disclosed partial inferior colliculi destruction and medial geniculate body degeneration. A pure tone audiogram revealed only moderate sensorineural hearing loss, but her speech perception was totally impaired. The binaural sound localization function was also impaired. The auditory brain stem response (ABR) showed waves I, III, and V to have normal latencies. The amplitude of wave III was larger than that of wave V. These results support the view that the waves of the ABR are elicited from multiple sources in the auditory brain stem nuclei and tracts. This case suggests a substantial role for the inferior colliculus and medial geniculate body in the processing of speech perception and sound localization.