Aphasia after left thalamic infarction

Subcortical Aphasia

PURPOSE OF REVIEW

Subcortical structures have long been thought to play a role in language processing. Increasingly spirited debates on language studies, arising from as early as the nineteenth century, grew remarkably sophisticated as the years pass. In the context of non-thalamic aphasia, a few theoretical frameworks have been laid out. The disconnection hypothesis postulates that basal ganglia insults result in aphasia due to a rupture of connectivity between Broca and Wernicke's areas. A second viewpoint conjectures that the basal ganglia would more directly partake in language processing, and a third stream proclaims that aphasia would stem from cortical deafferentation. On the other hand, thalamic aphasia is more predominantly deemed as a resultant of diaschisis. This article reviews the above topics with recent findings on deep brain stimulation, neurophysiology, and aphasiology.

RECENT FINDINGS

The more recent approach conceptualizes non-thalamic aphasias as the offspring of unpredictable cortical hypoperfusion. Regarding the thalamus, there is mounting evidence now pointing to leading contributions of the pulvinar/lateral posterior nucleus and the anterior/ventral anterior thalamus to language disturbances. While the former appears to relate to lexical-semantic indiscrimination, the latter seems to bring about a severe breakdown in word selection and/or spontaneous top-down lexical-semantic operations. The characterization of subcortical aphasias and the role of the basal ganglia and thalamus in language processing continues to pose a challenge. Neuroimaging studies have pointed a path forward, and we believe that more recent methods such as tractography and connectivity studies will significantly expand our knowledge in this particular area of aphasiology.

Transient Aphasia Following Resection of a Thalamic Cavernous Malformation

BACKGROUND

The thalamus has a demonstrated role in language, particularly through its connectivity to frontal language cortices.

CASE DESCRIPTION

A 59-year-old man with transient mixed aphasia following resection of a left-sided thalamic cavernous malformation is reported. No operative complications were encountered, and there was no surgical contact with cortical language areas. The patient recovered full language function within a week postoperatively.

CONCLUSIONS

The role of thalamic nuclei in language processes and other reports of transient thalamic aphasia are reviewed.

Hypophonia as a sign of thalamus lesion: a case report

Hypophonia is a neurological sign usually seen after brainstem or peripheral damage, either at the recurrent laryngeal nerve or vocal cord level. However, it has been described as a sign of supratentorial strokes in a few studies, specifically when anterior and ventral thalamic involvement is reported. In addition, it is a prominent sign of other neurological disorders such as Parkinson disease and other extrapyramidal conditions. We describe a case of hypophonia secondary to a left thalamic hemorrhage, after a careful search of other potential causes of this deficit, and we discuss the underlying neuroanatomical circuits.

Apraxic agraphia following thalamic damage: Three new cases

Apraxic agraphia (AA) is a so-called peripheral writing disorder following disruption of the skilled movement plans of writing while the central processes that subserve spelling are intact. It has been observed in a variety of etiologically heterogeneous neurological disorders typically associated with lesions located in the language dominant parietal and frontal region. The condition is characterized by a hesitant, incomplete, imprecise or even illegible graphomotor output. Letter formation cannot be attributed to sensorimotor, extrapyramidal or cerebellar dysfunction affecting the writing limb. Detailed clinical, neurocognitive, neurolinguistic and (functional) neuroimaging characteristics of three unique cases are reported that developed AA following a thalamic stroke. In marked contrast to impaired handwriting, non-handwriting skills, such as oral spelling, were hardly impaired. Quantified Tc-99m ECD SPECT consistently showed a decreased perfusion in the anatomoclinically suspected prefrontal regions. The findings suggest crucial involvement of the anterior (and medial) portion of the left thalamus within the neural network subserving the graphomotor system. Functional neuroimaging findings seem to indicate that AA after focal thalamic damage represents a diaschisis phenomenon.

Dynamic-intentional thalamic aphasia: a failure of lexical-semantic self-activation

BACKGROUND

Previous research has described patients with aphasia from thalamic lesions, some of whom were non-fluent with intact comprehension, others who were fluent with impaired comprehension, and some of whom are non-fluent with impaired comprehension. Whereas these three subtypes usually have normal repetition, they had impaired naming, suggesting a deficit in lexical (phonological word forms)-semantic processing. We report a patient with a left thalamic hemorrhage in which lexical-semantic representations appear to be intact but the patient demonstrates an inability to spontaneously activate his lexical-semantic system.

METHODS

A 82-year-old, right-handed man presented with decreased verbal fluency and memory loss following a thalamic hemorrhage. Neuropsychological assessment revealed significant decrements in verbal fluency with intact naming, comprehension, repetition and vocabulary.

CONCLUSIONS

To the best of our knowledge this pattern of language disturbance, which mirrors dynamic aphasia induced by frontal lesions, has not previously been described with thalamic injury. The thalamus has strong connections with the frontal lobe and rather than degradation of lexical-semantic representations, this patient's thalamic lesion probably induced frontal lobe dysfunction with a failure to spontaneously active lexical semantic representations.

Cognitive, affective and behavioural disturbances following vascular thalamic lesions: a review

During the last decades, many studies have shown that the thalamus is crucially involved in language and cognition. We critically reviewed a study corpus of 465 patients with vascular thalamic lesions published in the literature since 1980. 42 out of 465 (9%) cases with isolated thalamic lesions allowed further neurocognitive analysis. On the neurolinguistic level, fluent output (=31/33; 93.9%), normal to mild impairment of repetition (=33/35; 94.3%), mild dysarthria (=8/9; 88.9%) and normal to mild impairment of auditory comprehension (=27/34; 79.4%) were most commonly found in the group of patients with left and bilateral thalamic lesions. The taxonomic label of thalamic aphasia applied to the majority of the patients with left thalamic damage (=7/11; 63.6%) and to one patient with bithalamic lesions (=1/1). On the neuropsychological level, almost 90% of the left thalamic and bithalamic patient group presented with amnestic problems, executive dysfunctions and behaviour and/or mood alterations. In addition, two thirds (2/3) of the patients with bilateral thalamic damage presented with a typical cluster of neurocognitive disturbances consisting of constructional apraxia, anosognosia, desorientation, global intellectual dysfunctioning, amnesia, and executive dysfunctions associated with behaviour and/or mood alterations. Our study supports the long-standing view of a 'lateralised linguistic thalamus' but restates the issue of a 'lateralised cognitive thalamus'. In addition, critical analysis of the available literature supports the view that aphasia following left or bithalamic damage constitutes a prototypical linguistic syndrome.

Speech and language disturbances due to subcortical lesions

Over the last few decades, the number of studies concerning the role of subcortical structures in cognition has increased due to advances in neuroimaging. We describe the language and speech disturbances found in 16 patients with subcortical lesions (9 in basal ganglia and 7 in thalamus), evaluated by CT scan, MRI, and SPECT. Language assessment included the Boston Diagnostic Aphasia Examination, Boston Naming Test, and Token Test. Motor-articulatory alterations predominated in the non-thalamic group; in the thalamic group, there was a higher frequency of language alterations, especially in naming and auditory comprehension; verbal memory and attentional impairments may have contributed to this. We also found hypoperfusion in cortical language areas, and therefore participation of cortical dysfunction cannot be ruled out.

Thalamus and language: interface with attention, memory and executive functions

Subcortical structures are in a strategic functional position within the cognitive networks. Their lesion can interfere with a great number of functions. We studied six patients with thalamic vascular lesions (three left sided, two right sided and one bilateral), to characterize their repercussion in the communicative abilities and the interface between language alterations and other cognitive abilities, as attention, memory and frontal executive. All patients were evaluated through a functional interview (discourse analysis), and the following batteries: Boston Diagnostic Aphasia Examination, Boston Naming Test, Token Test, Benton Visual Retention Test, Trail Making, Wisconsin Card Sorting and frontal scripts. All patients performed MRI and five underwent SPECT. Results show that these patients present impairment in several cognitive domains, especially attention and executive functions (working memory, planning and self-monitoring); those with right lesions have an additional visuospatial impairment. Such alterations interfere with language abilities, and this fact must be considered in the rehabilitation efforts.

Subcortical anarthria: a case report

A 56-year-old right-handed male with a history of hypertension and diabetes presented two episodes of stroke: The first affected territory was the left anterior coroidal artery (capsular and paracapsular infarcts at the level of the genu and posterior arm of the internal capsule) and the second was the right thalamus, due to a hematoma. Following the first stroke, the patient developed severe dysarthria and after the second stroke remained anarthric. The pathophysiology of the disorder is discussed, and the role of the left and right thalamus as far as speech is concerned is reviewed.

Subcortical aphasia

We critically review the literature on subcortical aphasia, suggest that a number of traditional concepts regarding mechanisms of aphasia are inconsistent with now abundant data, and propose several new hypotheses. The absence of aphasia in 17 reported cases of dominant hemisphere striatocapsular infarction and the finding of nearly every conceivable pattern of language impairment in 33 different reported cases of striatocapsular infarction provide strong evidence against a major direct role of the basal ganglia in language and against disconnection or diaschisis as mechanisms of nonthalamic subcortical aphasia. However, detailed consideration of the vascular events leading to striatocapsular infarction strongly suggests that associated linguistic deficits are predominantly related to sustained cortical hypoperfusion and infarction not visible on structural imaging studies. Thalamic disconnection, as may occur with striatocapsular infarcts with extension to the temporal stem and putamenal hemorrhages, may also contribute to the language deficits in some patients. Review of the literature on thalamic infarction, in conjunction with previously unreported anatomic details of four cases, suggests that what infarcts in the tuberothalamic artery territory and the occasional infarcts in the paramedian artery territory associated with aphasia have in common is damage to the frontal lobe-inferior thalamic peduncle-nucleus reticularis-center median system that may be involved in regulating the thalamic gate in attentional processes. Disruption of attentional gating in the pulvinar and lateral posterior nuclei resulting from such lesions may impair selection of specific neuronal networks in the projection field of these nuclei that serve as the substrate for lexical-semantic function, which is in effect a disruption of a type of working memory, as defined by Goldman-Rakic. We define this as a defect of selective engagement.

Lexical-semantic deficits in two patients with dominant thalamic infarction

Two patients with dominant thalamic infarction, one in the tuberothalamic artery territory, the other in the paramedian artery territory, demonstrated language impairment limited to word retrieval difficulties in spontaneous language and structured naming tasks. Using a cognitive neuropsychological model of lexical processing developed in the study of patients with cortical lesions. We carried out a detailed investigation of their lexical abilities. Both patients demonstrated impairment restricted to oral and written picture naming and oral naming to definition and spared performance on tasks of lexical comprehension, oral word reading, and writing to dictation, as well as syntactic comprehension and production. Naming impairment disproportionately affected lower frequency words, and word substitutions often corresponded to objects that were semantically-related to target words. We propose that our patients' word retrieval impairments reflect a failure of thalamic input to effectively engage the cortical networks subserving lexical semantic processing, leading to degraded levels of activation as the semantic system interfaces with subsequent stages of lexical processing.

Ischemic thalamic infarction in children: clinical presentation, etiology, and outcome

Clinical features of thalamic strokes have not been well delineated in children. Six children with ischemic thalamic infarcts (3 M, 3 F; age range: 21 months to 14 1/2 years) are reported. Three patients had infarction in the thalamoperforate artery territory and all had a decreased level of consciousness and hemiparesis; two of them also had associated ocular motility abnormalities. One patient with left thalamotuberal artery stroke presented with aphasia. Two patients with thalamogeniculate artery infarcts had hemiparesis and involvement of the posterior cerebral artery. Etiologic factors in our patients were: infectious vasculitis, congenital heart disease, migraine, and unknown in 1 patient each and trauma in 2 patients. Follow-up information was available for 5, 4 of whom recovered completely. One patient was left with a neurologic deficit. We conclude that the prognosis of ischemic thalamic strokes in children is relatively good.

Aphasia and infarction of the posterior cerebral artery territory

Spoken language disorders are rarely mentioned in superficial infarction of the posterior cerebral (PCA) territory. Two clinical types have been reported: transcortical sensory and amnesic aphasia. Between 1979 and 1990, we studied retrospectively 76 patients suffering from an occipitotemporal infarction located in the superficial territory of the posterior cerebral artery, all well documented by CT. Aphasia was one of the first and prominent signs in 18 cases. Middle cerebral artery concomitant infarction could have been the cause of language impairment in 10. In 8 patients aphasia was only explained by a PCA territory infarct. Three patients showed features of transcortical sensory aphasia. CT localization showed internal lobe and thalamic involvement of the dominant hemisphere. Five patients exhibited word finding impairment with various degrees of amnestic syndrome. The dominant internal temporal lobe was always affected. Dominant thalamus involvement was found in one case only. Some correlations between clinical features and anatomical support (vascular supply and anatomical structure) might be suggested in our 8 cases of aphasic disorders due to PCA infarcts. They are discussed and compared with data in the literature.

Subcortical aphasia: distinct profiles following left putaminal hemorrhage

Numerous reports of aphasia after subcortical lesions have produced incomplete agreement about basic clinico-anatomic correlations. Some disagreement has arisen from methodologic differences. To control for some of the common differences, we analyzed 13 patients with left putaminal hemorrhage controlled for location--subcortical but not thalamic, and for time postonset--studied in both acute and postacute epochs. There was no apparent correlation between lesion site and acute language profiles. During the postacute epoch, there were several distinct correlations between lesion site (postacute decreased CT density) and specific aphasia dimensions--nonfluency, impaired comprehension, and perhaps impaired repetition. Our correlations were compatible with comparably controlled cases in the literature. A corollary result of this study is that patients fluent during the early epoch are likely to have a better outcome, and those initially nonfluent have a poor prognosis for language recovery.

Thalamic stroke: correlation of clinical symptoms, somatosensory evoked potentials, and CT findings

We studied 18 patients with a single ischemic thalamic lesion, who had somatosensory disturbances and/or central pain in the opposite hemibody, by correlating their clinical symptoms, somatosensory evoked potentials (SEPs), and computed tomography (CT) findings. Patients were divided into three groups: (1) those with somatosensory deficits, central pain, and abnormal SEPs, which comprised two thirds of the patients (classic thalamic pain syndrome), (2) those with somatosensory deficits, no central pain, and abnormal SEPs (analgetic thalamic syndrome), and (3) those with almost normal sense perception, central pain, and normal SEPs (pure algetic thalamic syndrome). CT evidence of a paramedian or anterolateral thalamic lesion might be an indicator for the development of central pain, because these types of infarctions occurred only in patients with the classic thalamic syndrome or the pure algetic thalamic syndrome. The differentiation of the thalamic syndrome into three subtypes is of prognostic value, because patients with a loss of cortical SEPs and a posterolateral ischemic thalamic lesion on the CT scan probably will not exhibit central pain.

Dysarthria in bilateral thalamic infarction. A case study

A patient suffering from bilateral thalamic infarction in the region supplied by the paramedian arteries sparing the internal capsules underwent acoustic analysis of sentence utterances. The results were compared with the findings obtained in parkinsonian subjects, in patients with upper motor neuron lesions, and in normal subjects. Acoustic measurements revealed increased pitch, monotonous speech, rough voice quality, and normal speech tempo concomitant with articulatory impreciseness in terms of incomplete closure productions. This constellation resembled parkinsonian dysarthria. Damage to the thalamic projection area of the pallidal efferents, therefore, seems to be the most probable cause of the patient's speech disorders. In parkinsonian subjects stereotactical lesions of this structure ameliorate rigor, but not akinesia. Thus, our patient's speech deficits, and by analogy the corresponding parkinsonian dysarthric disturbances, may be considered akinetic signs.

Thalamic ataxia

Seventeen patients with hemiataxia as a manifestation of thalamic infarction were studied. Hemiataxia had the main clinical characteristics of a "cerebellar type" of ataxia, though it never occurred in isolation, being associated with ipsilateral sensory disturbance (hemiataxia-hypaesthesia) in 7 patients, with ipsilateral sensory disturbance and hemiparesis (hypaesthetic ataxic hemiparesis) in 8 patients, and with hemiparesis (ataxic hemiparesis) in 2 patients. Recovery was good, and in all patients the sensory and motor disturbances improved or cleared before the hemiataxia. All patients had an infarct involving the lateral part of the thalamus (thalamogeniculate territory in 16, tuberothalamic territory in 1), also affecting the posterior limb of the internal capsule (PLIC) in 7 patients. Hemiataxia seemed linked to involvement of the caudal part of the ventral lateral nucleus of the thalamus or the immediately adjacent medial part of the PLIC. These structures are near the corticospinal pathways and the ventral posterior nucleus of the thalamus, explaining why hemiataxia is associated with hemiparesis or hypaesthesia in this type of infarct.

Subcortical aphasia from a thalamic abscess

A patient is reported who was treated successfully for a left thalamic abscess that resulted in subcortical aphasia. A SPECT scan showed large areas of hypoperfusion in the cortex of the left hemisphere. At follow up after seven months there was marked improvement in the language disorder and the cortical hypoperfusion. It is suggested that aphasia in patients with subcortical lesions results from secondary cortical dysfunctions. The evidence is confined to patients with stroke lesions. The possible implications of this case on current theories of pathophysiological mechanisms, in particular the ischaemic penumbra theory and the cortical diaschisis theory, are briefly discussed. Cortical diaschisis may be the appropriate explanation in this patient.

Aphonia due to paramedian thalamo-subthalamic infarction. Remarks on two cases

We describe two patients in whom CT brain scans imaged paramedian thalamo-subthalamic infarcts in the territory of the thalamo-mesencephalic arteries. Such infarcts give rise to a complex syndrome marked by disturbances of consciousness and of eye movement and neuropsychological disorders, including attentional, memory and, more rarely, language deficits. A loss of voice volume may accompany aphasic disturbances but is exceedingly rare in isolation. In the cases described the aphonia, total but transient, was the only language disorder. The physiopathological mechanisms involved in aphonia are complex and controversial.

Language disturbances from mesencephalo-thalamic infarcts. Identification of thalamic nuclei by CT-reconstructions

The authors report the cases of two patients with CT-documented paramedian mesencephalo-thalamic infarcts, showing language disturbances. The first patient showed a non fluent, transcortical motor-like aphasia, the other had a fluent but severely paraphasic language disorder. The CT study disclosed that it was the dorso-median thalamic nucleus that was mostly involved in both cases. These findings agree with a few previous pathological studies suggesting that the paramedian thalamic nuclei, particularly the dorso-median nucleus may play some role in language disturbances. However the anatomical basis for thalamic aphasia remains speculative, taking into account the importance of cortical connections in the origin of subcortical neuropsychological disturbances.

Diencephalic amnesia: a reorientation towards tracts?

The principal thalamic and hypothalamic structures implicated in mnemonic information processing are the mediodorsal nucleus of the thalamus, the pulvinar, anterior thalamus, and laterodorsal nucleus, the mamillary body, and the mamillothalamic tract and internal medullary lamina. Determining the contribution of an individual region in memory is quite difficult as it is nearly impossible to find a circumscribed damage of only one region. On the contrary, some illnesses affecting primarily the diencephalon, such as Korsakoff's disease, tend to involve several structures together. Furthermore, even when cases with similar circumscribed diencephalic damage can be found, these will not necessarily demonstrate the same outcome on the behavioral level. Therefore, the role or contribution of individual memory-related diencephalic structures has to be inferred by comparing a number of cases and by then extracting distinct features common to a given group. Such an approach revealed that the contributions of the two fiber systems mentioned above, mamillothalamic tract and internal medullary lamina, might be more important in processing information long-term than had been acknowledged previously and might be more important than that of the nuclear masses mentioned, especially of the mediodorsal thalamus. This outcome underlines the view that emphasizing interactions between brain regions rather than single static masses will provide a more realistic picture of how the nervous system acts in information processing.

Aphonia as the only speech disturbance from bilateral paramedian thalamic infarction

We examined a 55-year-old right-handed woman showing transient coma, amnesia, mild right hemiparesis, vertical gaze impairment and aphonia without aphasia. CT-scanning revealed bilateral paramedian thalamic infarction in the territory of the thalamo-subthalamic paramedian arteries. Aphonia may occur as a consequence of thalamic lesions, but until now it has not been described as an isolated speech disturbance.

Cerebral blood flow in thalamic aphasia

A 59-year-old man is reported, who became aphasic after left thalamic infarction, shown by CT. His speech was fluent, with reduced voice volume, impaired auditory and reading comprehension, verbal paraphasias but intact repetition skills. A single photon emission computed tomography (SPECT) scan to measure regional cerebral flow (rCBF) showed a reduction of flow in the parietotemporal areas of the left hemisphere. It is suggested that thalamic aphasia could result from structural subcortical damage with a homolateral functional cortical deficit leading to the specific aphasic disturbance.

Aphasia arising from purely deep lesions

In this study we investigated the relationship between deep-seated lesions of the left hemisphere and the aphasic disturbances. Thirty-seven vascular patients with CT-scan, language and neuropsychological examination carried out between 15 and 60 days post-onset were studied. Presence and frequency of apraxic disorders and acalculia are also reported. A consistent relationship between the site of the lesion and the pattern of aphasic disturbances could not be established. The most striking finding was a dissociation between oral and written expression, the latter being disproportionately impaired in a number of subjects.

Aphasia does not always follow left thalamic hemorrhage: a study of five negative cases

Five right-handed patients suffering from a recent CT-assessed left posterior thalamic hemorrhage are reported. In all patients a standard language examination performed within one month after stroke onset did not reveal aphasic disturbances. While the present series argues for the role of intrathalamic lesion localization, a review of the literature suggests that lesion site per se does not always account for the presence or absence of aphasia in the individual case. The importance of reduced blood flow and metabolism in cortical areas which appear undamaged on CT scan is briefly discussed.

Unilateral left paramedian infarction of thalamus and midbrain: a clinico-pathological study

In a patient with a unilateral embolic infarct in the left posterior thalamo-subthalamic paramedian artery territory, neuropathological studies showed involvement of the intralaminar, dorsomedial, and internal part of the ventral posterior nuclei of the thalamus, of the rostral part of the mesencephalic reticular formation, and of the posterior commissure. The patient showed upgaze palsy for voluntary saccades, smooth pursuit and vestibulo-ocular movements, sustained downgaze, right-sided motor hemineglect and facio-brachial hypaesthesia, motor transcortical aphasia and anterograde amnesia. This case confirms that unilateral destruction of the posterior commissure, rostral interstitial nucleus of the MLF and interstitial nucleus of Cajal produces a non-dissociated upgaze palsy. Involvement of the nucleus of Cajal probably produced the sustained downward deviation of the eye, by causing predominance of downward vestibulo-ocular inputs. This case also shows that thalamic aphasia and anterograde amnesia may be related to a paramedian lesion of the thalamus, with special reference to involvement of the dorsomedial nucleus, in the absence of lesion of the pulvinar and mamillo-thalamic tract and of conspicuous involvement of the ventral lateral nucleus. Selective hemineglect for motor tasks may occur in infarction of the dominant thalamus, involving the intralaminar nuclei.