Are signs of ocular tilt reaction in patients with cerebellar lesions mediated by the dentate nucleus?

A sensitive clinical sign of a vestibular tone imbalance in the roll plane is the ocular tilt reaction (OTR), a combination of skew deviation, ocular torsion and head and perceptual tilts such as tilts of the subjective visual vertical (SVV). Of these OTR components tilts of SVV are the most frequent. While these signs are regularly seen in patients with unilateral brainstem lesions, only a few case studies are available on their occurrence in patients with cerebellar lesions. Thus, the question arises whether cerebellar structures may be involved in contra- and/or ipsiversive tilts of the perceived vertical and other signs of OTR. We used lesion-mapping techniques in a total of 31 patients with acute cerebellar strokes, all showing at least a significant tilt of SVV. Twenty-three patients had a contraversive tilt of the SVV; they were compared with eight patients with ipsiversive tilts. MRI/CT lesion mapping revealed that in patients showing contraversive signs of OTR in general and contraversive SVV tilts in particular the dentate nucleus was the commonly damaged structure. In contrast, in ipsiversive signs of OTR, the dentate nucleus was spared and lesions were located in the biventer lobule, the middle cerebellar peduncle, the tonsil and the inferior semilunar lobule. These data suggest that the dentate nucleus is a critical anatomical structure within the cerebellum, belonging to a network involved in vestibular processing such as the perception of verticality. Therefore, a lesion of the dentate nucleus can lead to tilts of the SVV in the contraversive direction, i.e. a vestibular tone imbalance to the contralateral side, whereas cerebellar lesions excluding the dentate nucleus can induce a tone imbalance to the ipsilesional side.

Interaction of somatoform and vestibular disorders

BACKGROUND

The high coincidence of organic vestibular and somatoform vertigo syndromes has appeared to support pathogenic models showing a strong linkage between them. It was hypothesised that a persisting vestibular dysfunction causes the development of anxiety disorders.

OBJECTIVE

To determine the relation between vestibular deficits and somatoform vertigo disorders in an interdisciplinary prospective study.

METHODS

Participants were divided into eight diagnostic groups: healthy volunteers (n=26) and patients with benign paroxysmal positioning vertigo (BPPV, n=11), vestibular neuritis (n=11), Menière's disease (n=7), vestibular migraine (n=15), anxiety (n=23), depression (n=12), or somatoform disorders (n=22). Neuro-otological diagnostic procedures included electro-oculography with rotatory and caloric testing, orthoptic examination with measurements of subjective visual vertical (SVV) and ocular torsion, and a neurological examination. Psychosomatic diagnostic procedures comprised interviews and psychometric instruments.

RESULTS

Patients with BPPV (35.3%) and with vestibular neuritis (52.2%) had pathological test values on caloric irrigation (p<0.001). Otolith dysfunction with pathological tilts of SVV and ocular torsion was found only in patients with vestibular neuritis (p<0.001). Patients with Menière's disease, vestibular migraine, and psychiatric disorders showed normal parameters for vestibular testing but pathological values for psychometric measures. There was no correlation between pathological neurological and pathological psychometric parameters.

CONCLUSIONS

High anxiety scores are not a result of vestibular deficits or dysfunction. Patients with Menière's disease and vestibular migraine but not vestibular deficits showed the highest psychiatric comorbidity. Thus the course of vertigo syndromes and the possibility of a pre-existing psychopathological personality should be considered pathogenic factors in any linkage between organic and psychometric vertigo syndromes.

Thalamic infarctions cause side-specific suppression of vestibular cortex activations

H2O15-PET was performed during caloric vestibular stimulation of the right and left external ears in eight right-handed patients with acute unilateral infarctions or haemorrhages of the posterolateral thalamus (four right, four left). The posterolateral thalamus is the relay station for ipsi- and contralateral ascending vestibular input to the multiple multisensory vestibular cortex areas. The aim of this study was to evaluate the differential effects of unilateral vestibular thalamic lesions on thalamo-cortical projections, right hemispheric dominance and reciprocal inhibitory visual-vestibular interaction, as well as perceptual and ocular motor consequences during caloric irrigation. The major findings of the group analyses of the patients with right-sided and those with left-sided lesions were as follows: (i) activation of the multisensory vestibular temporo-parietal cortex was significantly reduced in the hemisphere ipsilateral to the thalamic lesion when the ipsilesional or contralesional ear was stimulated; (ii) activation of multisensory vestibular cortex areas of the hemisphere contralateral to the irrigated ipsilesional ear was also diminished; and (iii) the right hemispheric dominance in right-handers described above was preserved in those with right and left thalamic lesions. Simultaneous deactivations were often restricted to only one hemisphere--the one contralateral to the stimulation and contralateral to the vestibular cortex areas activated. There was, however, one area in the inferior insula which was also activated by either right or left ear stimulation in the hemisphere ipsilateral to the lesion. This supports the assumption that there is a bilateral direct ascending vestibular projection from the vestibular nuclei to the inferior part of the insula, which bypasses the posterolateral thalamus and is stronger in the right hemisphere. The cortical asymmetry of the pattern of activation during horizontal semicircular canal stimulation by calorics was not associated with a significant direction-specific asymmetry of caloric nystagmus or perceived body motion. Thus, the data demonstrate the functional importance of the posterolateral thalamus as a unique relay station for vestibular input to the cortex, of the dominance of the right hemisphere in right-handedness, and of ipsilateral ascending pathways. Furthermore, the normal interaction between the two sensory systems--the vestibular and the visual--appears to be impaired.

Preserved visual-vestibular interaction in patients with bilateral vestibular failure

BACKGROUND

During caloric vestibular stimulation, subjects showed bilateral activation of the vestibular cortex in the posterior insula and retroinsular region as well as concurrent deactivation of visual cortex areas bilaterally. This finding was the basis for the concept of a reciprocal inhibitory interaction between the vestibular and the visual systems.

OBJECTIVE

To analyze the modulations of this activation and deactivation pattern in patients with loss of vestibular input, that is, in patients with bilateral vestibular failure (BVF).

METHODS

Modulations of regional cerebral blood flow (rCBF) in PET were measured in nine patients with BVF and compared with those in healthy volunteers using statistical group as well as single-subject analyses (Statistical Parametric Mapping 96b).

RESULTS

The group analysis of the BVF patients showed only one small region of activation in the posterior insula contralateral to the stimulated ear, whereas the other areas correlating with vestibular, autonomic, and ocular motor function were not activated. Furthermore, the concurrent rCBF decreases of the primary visual cortex seen in healthy volunteers were not found in the patients. These decreases seem to be dependent on an intact vestibular input with concurrent vestibular nystagmus.

CONCLUSIONS

The results are compatible with the concept of a reciprocal inhibitory sensorisensory interaction between the vestibular and visual systems that normally act together for orientation in space and perception of motion. This interaction appears to be preserved in the patients at a significantly lower level, that is, with less activation and less deactivation.

Dominance for vestibular cortical function in the non-dominant hemisphere

The aim of this (15)O-labelled H(2)O bolus positron emission tomography (PET) study was to analyse the hemispheric dominance of the vestibular cortical system. Therefore, the differential effects of caloric vestibular stimulation (right or left ear irrigation with warm water at 44 degrees C) on cortical and subcortical activation were studied in 12 right-handed and 12 left-handed healthy volunteers. Caloric irrigation induces a direction-specific sensation of rotation and nystagmus. Significant regional cerebral blood flow increases were found in a network within both hemispheres, including the superior frontal gyrus/sulcus, the precentral gyrus and the inferior parietal lobule with the supramarginal gyrus. These areas correspond best to the cortical ocular motor centres, namely the prefrontal cortex, the frontal eye field and the parietal eye field, known to be involved in the processing of caloric nystagmus. Furthermore, distinct temporo-parietal activations could be separated in the posterior part of the insula with the adjacent superior temporal gyrus, the inferior parietal lobule and precuneus. These areas fit best to the human homologues of multisensory vestibular cortex areas identified in the monkey and correspond to the parieto-insular vestibular cortex (PIVC), the visual temporal sylvian area (VTS) and areas 7 and 6. Further cortical activations were seen in the anterior insula, the inferior frontal gyrus and anterior cingulum. The subcortical activation pattern in the putamen, thalamus and midbrain is consistent with the organization of efferent ocular motor pathways. Cortical and subcortical activation of the described areas was bilateral during monaural stimulation, but predominant in the hemisphere ipsilateral to the stimulated ear and exhibited a significant right hemispheric dominance for vestibular and ocular motor structures in right-handed volunteers. Similarly, a significant left hemispheric dominance was found in the 12 left-handed volunteers. Thus, this PET study showed for the first time that cortical and subcortical activation by vestibular caloric stimulation depends (i) on the handedness of the subjects and (ii) on the side of the stimulated ear. Maximum activation was therefore found when the non-dominant hemisphere was ipsilateral to the stimulated ear, i.e. in the right hemisphere of right-handed subjects during caloric irrigation of the right ear and in the left hemisphere of left-handed subjects during caloric irrigation of the left ear. The localization of handedness and vestibular dominance in opposite hemispheres might conceivably indicate that the vestibular system and its hemispheric dominance, which matures earlier during ontogenesis, determine right- or left-handedness.

Detection of Mycoplasma pneumoniae DNA in cerebrospinal fluid of a patient with M. pneumoniae infection-"associated" stroke

A 36-year-old woman presented with an acute ischemic stroke and a concomitant Mycoplasma pneumoniae infection that had been proven clinically, bacteriologically, and serologically. M. pneumoniae DNA was demonstrated in cerebrospinal fluid by positive nested polymerase chain reaction, and intrathecal antibody production was also detected. Contrary to previous reports about M. pneumoniae-associated stroke, most thrombostatic abnormalities in this patient occurred after stroke onset. Although the cause of stroke remains unclear in this patient, central nervous system invasion of M. pneumoniae DNA has to be considered a possible cause in rare cases of cerebral ischemia.

Multisensory cortical signal increases and decreases during vestibular galvanic stimulation (fMRI)

Functional magnetic resonance imaging blood-oxygenation-level-dependent (BOLD) signal increases (activations) and BOLD signal decreases ("deactivations") were compared in six healthy volunteers during galvanic vestibular (mastoid) and galvanic cutaneous (neck) stimulation in order to differentiate vestibular from ocular motor and nociceptive functions. By calculating the contrast for vestibular activation minus cutaneous activation for the group, we found activations in the anterior parts of the insula, the paramedian and dorsolateral thalamus, the putamen, the inferior parietal lobule [Brodmann area (BA) 40], the precentral gyrus (frontal eye field, BA 6), the middle frontal gyrus (prefrontal cortex, BA 46/9), the middle temporal gyrus (BA 37), the superior temporal gyrus (BA 22), and the anterior cingulate gyrus (BA 32) as well as in both cerebellar hemispheres. These activations can be attributed to multisensory vestibular and ocular motor functions. Single-subject analysis in addition showed distinctly nonoverlapping activations in the posterior insula, which corresponds to the parieto-insular vestibular cortex in the monkey. During vestibular stimulation, there was also a significant signal decrease in the visual cortex (BA 18, 19), which spared BA 17. A different "deactivation" was found during cutaneous stimulation; it included upper parieto-occipital areas in the middle temporal and occipital gyri (BA 19/39/18). Under both stimulation conditions, there were signal decreases in the somatosensory cortex (BA 2/3/4). Stimulus-dependent, inhibitory vestibular-visual, and nociceptive-somatosensory interactions may be functionally significant for processing perception and sensorimotor control.

Breast imaging with positron emission tomography and fluorine-18 fluorodeoxyglucose: use and limitations

PURPOSE

To evaluate the diagnostic value of positron emission tomography (PET) using fluorine-18 fluorodeoxyglucose (FDG) for the diagnosis of primary breast cancer.

PATIENTS AND METHODS

Preoperatively, 144 patients with masses suggestive of breast cancer underwent PET imaging of the breast. To identify breast cancer by increased metabolic activity, parametric FDG-PET images were analyzed for increased tracer uptake applying conventional image reading (CIR) and sensitive image reading (SIR). One hundred eighty-five breast tumors were evaluated by histology, revealing 132 breast carcinomas and 53 benign masses.

RESULTS

Breast carcinomas were identified with an overall sensitivity of 64.4% (CIR) and 80.3% (SIR). The increase in sensitivity (SIR) resulted in a noticeable decrease in specificity, from 94.3% (CIR) to 75.5% (SIR). At stage pT1, only 30 (68.2%) of 44 breast carcinomas were detected, compared with 57 (91.9%) of 62 at stage pT2. A higher percentage of invasive lobular carcinomas were false-negative (65.2%) compared with invasive ductal carcinomas (23.7%). Nevertheless, positive PET scans provided a high positive-predictive value (96.6%) for breast cancer.

CONCLUSION

Partial volume effects and varying metabolic activity (dependent on tumor type) seem to represent the most significant limitations for the routine diagnostic application of PET. The number of invasive procedures is therefore unlikely to be significantly reduced by PET imaging in patients presenting with abnormal mammography. However, the high positive-predictive value, resulting from the increased metabolic activity of malignant tissue, may be used with carefully selected subsets of patients as well as to determine the extent of disease or to assess therapy response.

Hemifield visual motion stimulation: an example of interhemispheric crosstalk

Coherent motion stimulation of the right or left visual hemifield was performed in nine healthy volunteers in order to investigate interhemispheric visuo-visual interaction by means of functional magnetic resonance imaging. The vertical edge of the motion pattern field was located 8 degrees distant from the fixation point to avoid stimulating the vertical meridian, which is represented retinotopically in both hemispheres. Bilateral activation was significant in the middle occipital gyrus (motion-sensitive middle temporal/middle superior temporal areas; BA 19/37). A negative signal change was found in the primary visual cortex including the lingual and fusiform gyri (BA 18/17) and the occipital white matter containing the optic radiation contralateral to the stimulated hemisphere. These data are most compatible with an interhemispheric transfer of visual motion information, most likely through the corpus callosum. Transcallosal transfer of visual motion information, evident as increases (BA 19/37) and decreases (BA 18/17) of the fMRI signals, may be functionally significant for the processing of motion perception.

Breast imaging with fluorine-18-FDG PET: quantitative image analysis

This study evaluated various quantitative criteria for analysis of breast imaging with PET using the radiolabeled glucose analog 18F-fluorodeoxyglucose (FDG).

METHODS

In a prospective study, 73 patients with abnormal mammography or palpable breast masses scheduled for biopsy were investigated with PET. A total of 97 breast tumors were evaluated by histology, including 46 benign and 51 malignant tumors. Using a whole-body PET scanner, attenuation-corrected images were acquired between 40 and 60 min after tracer injection. For Patlak analysis, dynamic data acquisition was obtained in 24 patients. To differentiate between benign and malignant breast tumors, receiver operating characteristic curves were calculated using incrementally increasing threshold values for tumor/ nontumor ratios based on average and maximum activity values per region of interest, standardized uptake values (corrected for partial volume effect, normalized to blood glucose, partial volume effect and blood glucose, using the lean body mass as well as the body surface area) and calculating the FDG influx rate (K) assessed by Patlak analysis.

RESULTS

Quantification of FDG uptake in breast tumors provided objective criteria for differentiation between benign and malignant tissue with similar diagnostic accuracy as compared with visual analysis. Applying correction for partial volume effect and normalization by blood glucose yielded the highest diagnostic accuracy.

CONCLUSIONS

These quantitative methods provided accurate evaluation of PET data for differentiating benign from malignant breast tumors. Quantitative assessment is recommended to complement visual image interpretation with the potential benefit of reduced interobserver variability.

Metabolic characterization of breast tumors with positron emission tomography using F-18 fluorodeoxyglucose

PURPOSE

To evaluate the diagnostic value of position emission tomographic (PET) imaging with F-18 fluorodeoxyglucose (FDG) in differentiating between benign and malignant breast tumors.

PATIENTS AND METHODS

Fifty-one patients, with suspicious breast lesions newly discovered either by physical examination or by mammography, underwent PET imaging before exploratory surgery. FDG-PET images of the breast were analyzed visually and quantitatively for objective assessment of regional tracer uptake.

RESULTS

Primary breast cancer was identified visually with a sensitivity of 68% to 94% and a specificity of 84% to 97% depending on criteria used for image interpretation. Quantitative analysis of FDG uptake in tumors using standardized uptake values (SUV) showed a significant difference between benign (1.4 +/- 0.5) and malignant (3.3 +/- 1.8) breast tumors (P < .01). Receiver operating characteristic (ROC) curve analysis exhibited a sensitivity of 75% and a specificity of 100% at a threshold SUV value of 2.5. Sensitivity increased to 92% with a corresponding specificity of 97% when partial volume correction of FDG uptake was performed based on independent anatomic information.

CONCLUSION

PET imaging allowed accurate differentiation between benign and malignant breast tumors providing a high specificity. Sensitivity for detection of small breast cancer ( < 1 cm) was limited due to partial volume effects. Quantitative image analysis combined with partial volume correction may be necessary to exploit fully the diagnostic accuracy. PET imaging may be helpful as a complimentary method in a subgroup of patients with indeterminate results of conventional breast imaging.

Tracheal substitution in dogs with reinforced Gore-Tex prosthesis

Reinforced Gore-Tex prostheses were implanted into the trachea, above the bifurcation, in 11 dogs. The first 3 animals died within a few days, due to an inappropriate surgical technique. The remaining animals were subjected to an adequate surgical procedure and all survived for a period of at least several months, except one which died of an esophago-tracheal fistula after 6 weeks. Ingrowth of respiratory epithelium into the prostheses was observed 5 to 7 weeks postoperatively.