Neuroradiology

, Volume 55, Issue 4, pp 413–421

Functional lesions in dysphagia due to acute stroke: discordance between abnormal findings of bedside swallowing assessment and aspiration on videofluorography

Authors

  • Aiko Osawa
    • Department of Rehabilitation MedicineSaitama Medical University International Medical Center
    • Department of Rehabilitation MedicineSaitama Medical University International Medical Center
  • Hiroshi Matsuda
    • Department of Nuclear MedicineSaitama Medical University International Medical Center
  • Norio Tanahashi
    • Department of NeurologySaitama Medical University International Medical Center
Diagnostic Neuroradiology

DOI: 10.1007/s00234-012-1117-6

Cite this article as:
Osawa, A., Maeshima, S., Matsuda, H. et al. Neuroradiology (2013) 55: 413. doi:10.1007/s00234-012-1117-6

Abstract

Introduction

Bedside swallowing assessments are often used to assess dysphagia. However, in some patients, aspiration pneumonia occurs without any problems on bedside swallowing assessments and some patients do not suffer aspiration pneumonia despite abnormal results of bedside swallowing assessments in acute stroke. To detect the differences of lesions related to bedside swallowing assessment abnormality and aspiration, we investigated swallowing-related functional lesions in terms of cerebral blood flow in patients with dysphagia after stroke.

Methods

The study included 50 acute stroke patients who underwent bedside swallowing assessments and videofluorography as well as single-photon emission computed tomography (CT) at approximately the same time. Bedside swallowing assessments included repetitive saliva swallowing test and modified water swallowing test as dry and wet swallowing tasks. The presence or absence of aspiration was assessed using videofluorography. We divided patients into three subgroups based on the outcomes of the bedside swallowing assessments and presence or absence of aspiration. Statistical image analysis was performed using single-photon emission CT to determine their relationship with bedside swallowing assessments and videofluorography results.

Results

Twenty-seven (54.0 %) and 28 (56.0 %) patients had abnormal repetitive saliva swallowing test and modified water swallowing test results. Videofluorography indicated aspiration in 35 (70.0 %) patients. In comparing patients with and without abnormal results on each test, the groups with abnormal repetitive saliva swallowing test, abnormal modified water swallowing test, and aspiration demonstrated lower cerebral blood flow in the left precuneus, left insula, and anterior cingulate gyrus, respectively.

Conclusions

Based on the analysis of cerebral blood flow, functional lesions differed across abnormal repetitive saliva swallowing test and abnormal modified water swallowing test findings and aspiration on videofluorography, and each test may assess different functions among the many processes involved in swallowing.

Keywords

StrokeSwallowingDysphagiaCerebral blood flowVideofluorography

Introduction

The acute phase of stroke is associated with dysphagia in 40–70 % of patients [1, 2], and eating without knowledge of the dysphagia can lead not only to pneumonia but also to life-threatening conditions such as dehydration, malnutrition, and suffocation [3, 4]. However, oral feeding is an important component of human socialization, and dysphagia may lead to social retraction and isolation and subsequently to low self-esteem and quality of life [5, 6]. In addition, malnutrition after the first week of admission has been identified as an independent poor prognostic factor [7]. Therefore, the assessment of aspiration risk does not constitute the only objective in the evaluation of dysphagic stroke patients, in whom potential feeding problems should also be addressed [8]. During the acute phase of stroke, it is important to perform a bedside swallowing assessment (BSA) [914] and often also videofluorography (VF) or fiberendoscopic evaluation of swallowing with the goal of early oral feeding initiation. Tasks vary across different BSA tests, and differing results may reflect various types of dysphagia.

Lesions not only in the brainstem [15] but also in the cerebral cortex, such as the insula [16, 17] and posterior central gyrus [18], and in subcortical structures including basal ganglia [19] have been associated with dysphagia. Recently, the cerebral cortex and subcortex have also been well established to play an important functional role in the regulation of swallowing. In a study using functional MRI (fMRI) to compare the functional anatomy of swallowing in unilateral hemispheric stroke patients and healthy adults, cerebral activation during swallowing tasks was localized to the precentral, postcentral, and anterior cingulate gyri, insula, and thalamus [20]. However, in clinical settings, a mixture of recurrent cases and cases of multiple lesions makes identifying specific lesions related to dysphagia difficult. Additionally, we often experience aspiration pneumonia after resumed eating without any problems detected on BSA in the acute stroke phase. One common reason for this discrepancy is that bedside assessments cannot detect silent aspiration. However, no reports have investigated on the possible differences between lesions that relate to abnormality on bedside assessments and aspiration on VF.

In this study, we measured regional cerebral blood flow using single-photon emission computed tomography (SPECT) in patients with dysphagia suffering from acute stroke to clarify the differences in functional lesions related to different BSA tasks and differences between the lesions associated with BSA abnormalities and aspiration on VF.

Methods

Subjects

Five hundred seventy patients with acute stroke were referred to the rehabilitation department from June 2008 to May 2009, of which 50 patients were chosen for analysis in this retrospective study. We assessed swallowing function using BSA for all stroke patients without unconsciousness. If dysphagia continued over 1 week and patients did not suffer from active aspiration pneumonia, we assessed swallowing function directly using VF. SPECT was performed for various reasons such as diagnosis of ischemic area, vascular cognitive impairment, and so on. The criteria for selecting patients in our study were all patients who underwent BSA and VF as well as SPECT at approximately the same time. Patients excluded from this analysis were those with surgical treatment and/or mechanical ventilation and patients with severe aphasia and/or dementia. The patients were 49–95 years of age (70.2 ± 10.3 years), with 32 men and 18 women. Thirty-two patients had cerebral infarction, and 18 had cerebral hemorrhage. On computed tomography (CT) and MRI, two patients presented with left cortical lesion, five with right cortical lesion, 17 with subcortical lesion, three with cerebellar lesion, six with brainstem lesion, and 17 with multiple lesions. Thirty-seven (74.0 %) patients had an initial stroke, and 13 (26.0 %) had a recurrent stroke; 16 (32.0 %) patients had bilateral lesions. The time interval between disease onset and the start of rehabilitation was 1–10 days (1.5 ± 1.8 days). The time interval from disease onset to BSA and VF was 1–20 days (9.7 ± 4.8 days), and the time between VF and SPECT was 3.4 ± 2.5 days (0–7 days). The approval of the institutional ethics committee (Saitama Medical University International Medical Center, IRB No. 11-018) was obtained.

Assessment of swallowing function

The repetitive saliva swallowing test (RSST) [11] and modified water swallowing test RSST (MWST) [12] were performed for BSA, as recommended by the Japan Guidelines for the Management of Stroke 2009 [21]. The RSST is performed by gently pressing the pads of the second and third fingers on the laryngeal prominence and hyoid bone of the patients and having the patients repeat voluntary saliva swallowing, and the test is interpreted as abnormal if the patients are unable to swallow more than three times within 30 s [11]. The MWST is a test scored on a five-point scale in which 3 ml cold water is poured into the vestibule of the mouth, and the patients are asked to voluntarily swallow and, if possible, to repeat voluntary saliva swallowing twice more (“Appendix”). When the score is 4 or higher, the test is repeated three times, and the worst swallow is rated. A score of 3 or lower is considered as abnormal [12].

VF was then used to monitor the actual swallowing movement. VF was performed according to the standard VF procedures established by the Japanese Society of Dysphagia Rehabilitation [22]. After assessing the level of consciousness and vital signs of the patients and confirming that the risks associated with VF were low, VF was performed using an X-ray fluoroscope with the attendance of a physician, speech therapist, administrative dietitian, and radiological technician. A contrast agent (barium sulfate) was mixed beforehand with boluses of test food with different textures and tastes, and the patients swallowed the boluses with feeding assistance. Jelly, yogurt, rice gruel, and fluid were used as test foods. At the start of the test, the patients were positioned in a 30° tilt, and when entrance into the larynx or aspiration was not observed, the tests were performed with the patients tilted at 60–90°. The VF results were interpreted by consensus of two physicians certified by the Japanese Society of Dysphagia Rehabilitation and speech pathologists to assess the presence or absence of aspiration. In this study, the investigators performing BSA and VF were blinded to the brain lesion and they performed BSA and VF with the same procedure, regardless of the brain lesion.

Neuroradiological study

A dose of 600 MBq technetium-99 m-l,l-ethyl cysteinate dimer (99mTc-ECD) was injected into the right cubital vein of the patients while at rest with their eyes closed. Global cerebral blood flow was calculated from the time activity curve in the brain and aortic arch using the Patlak Plot method [23]. All SPECT images were obtained using the Siemens two-detector SPECT/CT system (Symbia T6). The Siemens e-SOFTP was used as the data processing unit, and a low-energy high-resolution parallel collimator was used. The in-plane resolution of SPECT images was 9 mm at full-width at half maximum (FWHM). The cerebral blood flow SPECT images were reconstructed with a slice thickness of 3.3 mm and an acquisition matrix of 128 × 128 after CT attenuation correction.

In the statistical image analysis of relative difference in cerebral blood flow, SPECT data were transferred to a personal computer, and spatial normalization was applied for the transformation of the brain images into an original 99mTc-ECD template standardized to a brain atlas using Statistical Parametric Mapping (SPM8, http://www.fil.ion.ucl.ac.uk/spm/) [24]. Isotropic smoothing with a Gaussian kernel with 12-mm FWHM was employed to reduce anatomical individual differences that could not be corrected by spatial normalization. For statistical inference, SPECT data were analyzed with a general linear model using SPM8. The overall mean global cerebral blood flow was treated as a confounding covariate.

A proportional scaling routine was used to achieve global normalization of voxel values between SPECT data. A design matrix was constructed for two-sample t-test between two groups of patients with normal and abnormal RSST, MWST, and VF results. Inferences were obtained on t-contrasts. SPM{t} were transformed to the unit normal distribution {SPM(Z)} and thresholded at P < 0.05, P < 0.01, and P < 0.001. The significance of each region was estimated without correction for multiple comparisons. Extent threshold was set to 0 voxels.

Group classification

We also assessed age, sex, etiology of stroke (infarction/hemorrhage), Canadian Neurological Scale (CNS), Mini-mental State Examination (MMSE) results, and length of stay for all patients. CNS assessed stroke severity with a scale of 1.5 to 11.5 and more affected stroke patients have a lower score on it [25]. After assessment, the entire patient group was divided into three subgroups separately: (1) according to RSST outcome, (2) according to MWST outcome, and (3) based on the presence or absence of aspiration on VF. In addition, statistical image analysis of functional lesions was performed using SPECT to determine their relationship with the BSA and VF results among the three subgroups. Statistical software JMP 8.02 was used to analyze the data, and analysis of variance was used for group comparisons. The clinical characteristics, the results of other swallowing tests, and lesion location between two groups in each subgroup were compared using χ2 test (Fisher’s exact test). P values less than 0.05 were considered as statistically significant.

Results

Twenty-seven (54.0 %) patients had an abnormal RSST result, and 28 (56.0 %) patients had an abnormal MWST result. VF revealed aspiration in 35 (70.0 %) patients (Fig. 1). CNS and gender significantly differed between patients with normal and abnormal RSST results, but no differences were observed in age, etiology of stroke, and the time between disease onset and RSST (Table 1). No differences were observed in other demographic factors between patients with normal and abnormal MWST results (Table 2). Demographic, clinical, and morphological variables did not significantly differ according to the presence or absence of aspiration on VF (Table 3). Additionally, the results of other swallowing assessments, recurrence rate, and lesion location of stroke (cortical/subcortical/cerebellar/brainstem/multiple location) did not significantly differ on the basis of RSST, MWST, or aspiration status (Tables 1, 2, and 3). In the lesion side, patients with abnormal RSST had significantly more lesions on the left side (Table 1). The MMSE score of the abnormal RSST group was lower than that of the normal RSST group; however, the number of patients with aphasia was not significantly different between the two groups (Table 1). On the other hand, more aphasic patients were included, and their MMSE score was lower in the normal MWST group than in the abnormal MWST group (Table 2). No differences were observed in the number of patients with aphasia and MMSE score between the aspiration and non-aspiration groups (Table 3).
https://static-content.springer.com/image/art%3A10.1007%2Fs00234-012-1117-6/MediaObjects/234_2012_1117_Fig1_HTML.gif
Fig. 1

Correlation between patients with abnormal findings of bedside swallowing assessments and aspiration on VF. Twenty-seven patients had an abnormal RSST result, and 28 patients had an abnormal MWST result. VF revealed aspiration in 35 patients. Patients who showed abnormality in all the tests were 13

Table 1

Demographic, clinical, and morphological variables for normal vs. abnormal RSST results

 

Normal RSST

Abnormal RSST

p

N = 23

N = 27

Age, year (SD)

68.8 (11.6)

71.3 (9.1)

0.39

Gender, n, male/female

19/4

13/14

0.01

Etiology, n, infarction/hemorrhage

13/10

19/8

0.31

Canadian Neurological Scale, 11.5 (SD)

7.6 (2.8)

5.8 (2.4)

0.02

Mini-mental state examination, 30 (SD)

19.1 (6.2)

14.8 (8.4)

0.04

Aphasia, n (%)

4 (17.4)

12 (44.4)

0.07

Interval from onset to RSST

11.0 (5.1)

8.6 (4.4)

0.07

Length of stay, days (SD)

23.8 (8.2)

28.9 (11.1)

0.08

Abnormal MWST, n (%)

12 (52.2)

16 (59.3)

0.78

Aspiration on VF, n (%)

18 (78.3)

17 (63.0)

0.35

Recurrent stroke, n (%)

4 (17.4)

9 (33.3)

0.2

Bilateral lesion, n (%)

5 (21.7)

11 (40.7)

0.15

Lesion side, n, right/left/bilateral

13/5/5

4/12/11

0.01

Lesion location

  

0.24

 Cortical, n (%)

3 (13.0)

4 (14.8)

 

 Subcortical, n (%)

8 (34.8)

9 (33.3)

 

 Cerebellar, n (%)

3 (13.0)

0

 

 Brainstem, n (%)

3 (13.0)

3 (11.1)

 

 Multiple locations, n (%)

6 (26.1)

11 (40.7)

 
Table 2

Demographic, clinical, and morphological variables for normal vs. abnormal MWST results

 

Normal MWST

Abnormal MWST

p

N = 22

N = 28

Age, year (SD)

68.5 (11.8)

71.5 (8.9)

0.32

Gender, n, male/female

13/9

19/9

0.52

Etiology, n, infarction/hemorrhage

11/11

21/7

0.07

Canadian Neurological Scale, 11.5 (SD)

6.5 (2.9)

6.7 (2.7)

0.78

Mini-mental state examination, 30 (SD)

14.0 (8.0)

18.9 (6.9)

0.02

Aphasia, n (%)

11 (68.8)

5 (31.3)

0.03

Interval from onset to MWST

8.7 (4.0)

10.5 (5.3)

0.19

Length of stay, days (SD)

24.2 (8.2)

28.4 (11.2)

0.15

Abnormal MWST, n (%)

11 (50.0)

16 (57.1)

0.61

Aspiration on VF, n (%)

13 (59.1)

22 (78.6)

0.21

Recurrent stroke, n (%)

8 (36.4)

5 (17.9)

0.14

Bilateral lesion, n (%)

7 (31.8)

9 (32.1)

0.98

Lesion side, n, right/left/bilateral

6/9/7

11/8/9

0.58

Lesion location

  

0.17

 Cortical, n (%)

2 (9.1)

5 (17.9)

 

 Subcortical, n (%)

9 (40.9)

8 (28.6)

 

 Cerebellar, n (%)

3 (13.6)

0

 

 Brainstem, n (%)

1 (4.6)

5 (17.9)

 

 Multiple locations, n (%)

7 (31.8)

10 (35.7)

 
Table 3

Demographic, clinical, and morphological variables for the presence vs. absence of aspiration

 

Without aspiration

With aspiration

p

N = 15

N = 35

Age, year (SD)

69.3 (10.4)

70.5 (10.4)

0.71

Gender, n, male/female

9/6

23/12

0.7

Etiology, n, infarction/hemorrhage

10/5

22/13

0.8

Canadian Neurological Scale, 11.5 (SD)

6.4 (2.9)

6.7 (2.7)

0.69

Mini-mental state examination, 30 (SD)

15.2 (8.4)

17.5 (7.4)

0.35

Aphasia, n (%)

7 (46.7)

9 (25.7)

0.19

Interval from onset to VF

8.9 (4.4)

10.0 (4.9)

0.43

Length of stay, days (SD)

24.7 (8.8)

27.3 (10.7)

0.41

Abnormal MWST, n (%)

10 (66.7)

17 (48.6)

0.35

Aspiration on VF, n (%)

6 (40.0)

22 (62.9)

0.21

Recurrent stroke, n (%)

3 (20.0)

10 (28.6)

0.52

Bilateral lesion, n (%)

2 (13.3)

14 (40.0)

0.06

Lesion side, n, right/left/bilateral

6/7/2

11/10/4

0.14

Lesion location

  

0.37

 Cortical, n (%)

4 (26.7)

3 (8.6)

 

 Subcortical, n (%)

6 (40.0)

11 (31.4)

 

 Cerebellar, n (%)

1 (6.7)

2 (5.7)

 

 Brainstem, n (%)

2 (13.3)

4 (11.4)

 

 Multiple locations, n (%)

2 (13.3)

15 (42.9)

 
On functional SPECT images, SPM8 analysis demonstrated significant declines in the left precuneus (Brodmann areas <BA> 7) (−24.0, −70.0, 39.0, Talairach coordinate x, y, z; Z = 2.11) in patients with abnormal RSST compared to patients with normal RSST (Fig. 2), in the left insula (BA13) (−34.0, 9.0, 16.0, Talairach coordinate x, y, z; Z = 2.81) in patients with abnormal MWST compared to patients with normal MWST (Fig. 3), and in the anterior cingulate gyrus (BA24) (−2.0, 27.0, 18.0, Talairach coordinate x, y, z; Z = 2.96) in patients with aspiration on VF compared to patients without aspiration on VF (Fig. 4).
https://static-content.springer.com/image/art%3A10.1007%2Fs00234-012-1117-6/MediaObjects/234_2012_1117_Fig2_HTML.gif
Fig. 2

Result of group comparisons of the regional cerebral blood flow between the patients with abnormal RSST and with normal RSST. Cerebral blood flow in the left precuneus was significantly decreased in patients with abnormal RSST results compared to those with normal results

https://static-content.springer.com/image/art%3A10.1007%2Fs00234-012-1117-6/MediaObjects/234_2012_1117_Fig3_HTML.gif
Fig. 3

Result of group comparisons of the regional cerebral blood flow between the patients with abnormal MWST and with normal MWST. Cerebral blood flow in the left insular gyrus was significantly decreased in patients with abnormal MWST results compared to those with normal results

https://static-content.springer.com/image/art%3A10.1007%2Fs00234-012-1117-6/MediaObjects/234_2012_1117_Fig4_HTML.gif
Fig. 4

Result of group comparisons of the regional cerebral blood flow between the patients with aspiration and without aspiration as assessed by videofluorography. Cerebral blood flow in the anterior cingulate gyrus was significantly decreased in patients with the presence of aspiration as assessed by videofluorography compared to those with the absence of aspiration

Discussion

A multilayered neural network involving the cerebral cortex, subcortical structures, and brainstem mediates swallowing. Swallowing is a complex behavior with dynamic neural coordination at the cerebral as well as brainstem levels [26]. Therefore, the damage to these structures at any level can lead to dysphagia. In the various studies, not only the lower portion of the pons or medulla but also the unilateral cerebral lesions, cingulate gyrus, and insular gyrus involvement in the swallowing movement has been indicated [16, 18, 2729]. In the point of aspiration pneumonia, Okamura et al. [30] reported that regional cerebral blood flow in the bilateral anterior insular gyrus was significantly decreased in stroke patients with a history of aspiration of pneumonia as compared with those without such a history.

In stroke patients with dysphagia, however, only a few lesions can be identified with certainty, and recurrent cases and cases of multiple lesions are mixed. Specifically, a single patient may frequently have lesions in the acute phase as well as old lesions, making it difficult to identify which lesions are most strongly associated with dysphagia. Although more patients have dysphagia after recurrent stroke and both new and old lesions may contribute to dysphagia, no studies reflecting the actual clinical situation have investigated recurrent cases and cases of multiple lesions, and no reports have compared abnormal BSA results and lesions related to aspiration identified by VF.

In this study, we performed both BSA and VF during the acute phase of stroke which included recurrent and multiple lesions and almost simultaneously measured regional cerebral blood flow to compare the functional lesions detected. Abnormal RSST result was related to decreased regional cerebral blood flow in the left precuneus and abnormal MWST result was related to decreased regional cerebral blood flow in the left insular gyrus. RSST is a dry swallowing task, in which patients are instructed by verbal command to gather and swallow the saliva repeatedly. This may be the reason why patients with abnormal RSST had more left verbal-dominant side lesions. For getting a normal RSST, patients require not only correct verbal comprehension and verbal memory but also certain cognitive functions such as mental concentration. On the other hand, in MWST, water was placed on the floor of the mouth using a syringe. It is not so difficult to understand swallowing of water in the oral cavity for patients, even if they have aphasia or mental deterioration. In fact, the score of MMSE in abnormal RSST group was lower than that of normal RSST group and, on the contrary, the score of MMSE in normal MWST group was interestingly lower than in abnormal MWST group. These results reveal a comparatively close relation between the results of RSST and cognitive function, and the result of MWST is of little relevance to verbal and general cognitive function. Schroeder et al. [31] reported that certain clinical and neurocognitive behaviors were associated with swallowing outcomes, and Sellars et al. [32] reported subjects in acute stroke who developed pneumonia and had lower mental test score. For eating and swallowing, awareness of what kind of food they will eat and/or swallow and cognitive judging about how to eat and swallow safety are very important. In the early stage of Alzheimer’s disease, specific findings of regional perfusion reduction are observed in the posterior cingulate gyrus, precuneus, and parietal cortex [33], indicating that the precuneus is specifically related to cognitive function. Although there are few reports about the relationship between swallowing and cognitive function, the RSST may reflect a part of volitional control with cognitive-including function; therefore, it may be related to the precuneus in the left hemisphere due to its functional hemispheric dominance over language, unlike the MWST.

As noted earlier, on MWST, patients have to swallow the water in the oral cavity which was entered by others. We supposed that this test might reflect rather swallowing function itself than cognitive function because of the simpler task. The SPECT analysis in our study indicated that an abnormal MWST result was related to the left insular gyrus. In a previous report [34], the anterior insula appears to be a rich area of parallel connectivity closely associated with many cortical and subcortical areas that mediate swallowing, that is, premotor cortex; gustatory, olfactory, limbic, and autonomic structures; thalamus; and nucleus tractus solitarius. The insular cortex is considered to contribute to oral and pharyngeal motility through connectivity or inherent properties [16]. Especially, the anterior insula has been implicated in the processing of visceral sensation from the pharynx [35]. In the report which analyzed brain lesions for the patients whose pharyngeal delay time values tended to increase linearly as the swallowing trials proceeded, it was considered that damage to swallow-related areas may reduce their sensitivity to incoming signals from the oral cavity, thereby impairing preparations to generate motor command signals and compromising their ability to send sufficient voluntary descending command signals to activate the swallowing central pattern generator located in the medulla [36]. On MWST, patients have to sense water in their oral cavity and control the timing of swallowing using various neural networks. These previous reports and our new findings indicate that MWST may reflect the function of insula as an important transfer point on neural network for swallowing. However, we should remember that MWST could not detect silent aspiration.

Additionally, we assessed the presence or absence of actual aspiration on VF. Actual aspiration was related to a decrease in blood flow in the anterior cingulate gyrus. Cingulate gyrus involvement has been indicated in the motivation for swallowing, retrieval of memory, selection of responses [37], recognition of foods, and safe swallowing [38]. Several studies in healthy volunteers using fMRI, positron emission tomography, and magnetoencephalography have also reported the activation of the posterior cingulate gyrus [39] and anterior cingulate gyrus [18] prior to swallowing. During actual food intake without aspiration, motivation, impulse, and maintenance of arousal are important, and in stroke patients in the acute phase as investigated in our study, dysfunction of the anterior cingulate gyrus may be associated with an increased risk of aspiration.

The RSST and MWST are simple and easy techniques for bedside assessment of aspiration risk that are highly correlated with VF [11, 12]. In clinical settings, however, BSA alone sometimes does not provide sufficient information because some individuals cannot understand the purpose of the testing due to cognitive impairment or other reasons or because arousal levels can fluctuate in the acute phase. Additionally, our results indicate that each test may assess different functions in a multilayered neural network for swallowing at least at the early stage of stroke. Normally, performing both BSA and VF in all patients before the initiation of feeding is desirable, but the question of bed rest and the necessity of special equipment frequently lead to considerations of initiating oral feeding based only on BSA results.

Under such circumstances, our findings are very significant because they indicate a difference between abnormal BSA results and the location of functional lesions related to aspiration as detected by VF. Detecting asymptomatic aspiration is extremely difficult, and it may be missed by BSA alone [40, 41]. Some researchers reported that the presence of insular lesions is a predictor of dysphagia but not aspiration [18]. To prevent aspiration pneumonia after the initiation of oral feeding, especially during the acute phase of stroke, we have to pay attention to the presence or absence of lesions around the precuneus and insula. In addition, the functional state of cingulate gyrus, that is, the maintenance of optimal arousal and sufficient motivation and impulse to eat, may be considered as important requirements for the initiation of safe oral feeding.

Finally, again, we divided the same subjects into three subgroups separately based on the RSST, MWST, and VF outcome. Their lesion due to stroke varied from brainstem to cerebral cortex. Nevertheless, the areas of depressed regional blood flow in the patients with abnormal findings on the two different tests and VF were very specific and quite different. These findings may indicate a strong relationship between the results of swallowing assessment and the identified lesions as possibly decreased function. Because the present study aimed to clarify differences in functional lesions related to different BSA tasks and differences between abnormal bedside assessment findings and aspiration on VF in acute stroke patients, it did not include healthy subjects. Further studies are necessary to compare stroke patients and healthy subjects as well as to compare the acute phase and chronic phase after improvement of dysphagia in the same patients. Additionally age, lesion, and etiological–control study may be important to clarify the function of more detailed lesions that relate to swallowing following stroke.

Conclusions

Brain perfusion SPECT revealed functional lesions in acute stroke patients in the left precuneus to be associated with abnormal RSST, in the left insula to be associated with abnormal MWST, and in the anterior cingulate gyrus to be associated with aspiration on VF. Different lesions contribute to the results of each test, suggesting that the tests may assess different functions among the many processes involved in swallowing.

Conflict of interest

We declare that we have no conflict of interest.

Copyright information

© Springer-Verlag Berlin Heidelberg 2012