This study showed that (1) short- and long-term prognosis in isolated ACA territory infarction were good, (2) proximal ACA segment occlusion was an independently associated factor for developing distinctive symptoms in ACA territory infarction, and (3) the distinctive symptoms related to proximal ACA segment occlusion influenced dwelling and job status, regardless of positive mRS.
Short-term mortality after isolated ACA territory infarction can range between 0 and 8%, which is much lower than the 17.3% short-term mortality after MCA territory infarction [3, 8, 13]. Consistent with previous studies, only one patient (2.1%) died during the follow-up period in our study. Regarding functional outcomes, approximately 70% of patients achieved functional independence at three months in previous studies [13, 14]. In our study, 85.1% of patients had a good outcome at three months in isolated ACA territory infarction. Thus, short-term outcomes after isolated ACA territory infarction seemed to be favourable, and in line with previous research. However, little is known about the long-term prognosis after isolated ACA territory infarction. We investigated the long-term outcomes, with 87.2% of patients showing good outcomes at one year after discharge. Thus, similar to the short-term outcomes, the long-term outcomes in isolated ACA territory infarction also seem to be favourable.
The most common symptom in isolated ACA territory infarction was motor deficit, typically involving the lower extremity contralateral to the infarction site [3, 4, 8]. In our study, the median NIHSS sub-score for the leg was also higher than that for the arm [3]. Similar to previous studies, the symptoms in our patients also involved the lower extremity more than the upper extremity. This dominance of the involvement of the lower extremity originates in the paracentral lobule located in the ACA territory. On the contrary, the cortical area for the hand and arm is located in the MCA territory, and the corona radiata, where the projection fibres from the cortex were merged, is also located in the MCA territory. Therefore, developing hemiparesis is relatively uncommon in isolated ACA territory infarction, and preserving motor function in the arm may help achieve functional independence. In addition, motor function of the lower extremity usually recovers faster and more completely than that of the upper extremity [15]. This may be the reason why patients with isolated ACA territory infarction showed favourable functional independence as measured by mRS.
Distinctive symptoms in ACA territory infarction include altered mental status, abulia, mutism, decreased verbal fluency, aphasia, and urinary incontinence [3, 4]. Abulia and mutism are associated with cingulate gyrus and supplementary motor area involvement, which are important for human behaviour [16–18], while aphasia is associated with involvement of the supplementary motor area located in the superior medial frontal lobe [19, 20]. Urinary incontinence suggests involvement of the superior frontal gyrus, cingulate, and large infarction lesions affecting the superior and medial parts of the frontal lobe [21]. In terms of distinctive symptom development in ACA territory infarction, infarction size may be an influencing factor. Moreover, the structures associated with distinctive symptoms in the ACA territory are located at least above the A3 segment and classified as the proximal portion in our study. Thus, the risk of developing distinctive symptoms in the ACA territory seems to be high in cases of proximal ACA segment occlusion. As mentioned above, proximal ACA segment occlusion was an independent factor for the development of distinctive symptoms in ACA territory infarction.
Furthermore, the presence of distinctive symptoms in ACA territory infarction was closely associated with dwelling and job status in patients with good mRS.
According to the mRS, patients with a slight disability who were able to look after their own affairs without assistance, but unable to perform all previous activities, were given a score of 2.
However, if, for example, patients had mild aphasia or abulia with a mild degree of motor deficit, they could still take care of their own affairs since motor function was relatively good. In such cases, their outcome may have been classified as good, even if the patient’s family suffered from the after-effects of the distinctive symptoms of ACA territory infarction. Thus, the real prognosis after ACA territory infarction might not be correctly assessed by mRS alone, and it might be wrong to conclude, based on mRS, that patients with isolated ACA territory infarction had favourable outcomes.
Currently, mechanical thrombectomy (MT) is recommended as primary treatment for MCA and carotid artery occlusion [22, 23]. Because of its rarity, there are few studies of MT in ACA occlusion. The average A2 and A3 diameters were > 2.0 mm [24]. Thus, considering the minimal stent retriever diameter (3.00 mm), the proximal ACA segment was suitable for MT [25]. In a retrospective study of 30 patients, MT on ACA occlusions led to a good recanalization rate with few complications [26]. In addition, recent studies have shown that the presence of ACA occlusion by secondary embolism during MT for MCA without recanalization was associated with poor functional outcomes [27, 28]. Thus, if patients with proximal ACA segment occlusion arrived within the right therapeutic window of time, MT could be considered because proximal segment occlusion was associated with the development of distinctive symptoms in ACA territory infarction, which could affect future patient’s true prognosis, which could not be assessed with mRS alone.
This study had several limitations. First, this was a retrospective single-centre study with a small sample size. We did not use a validated questionnaire or examination to check for distinctive symptoms in ACA territory infarction. To circumvent these limitations, we plan to perform a prospective study with a validated questionnaire for the prognosis in ACA territory infarction.
Both short- and long-term prognoses based on mRS in isolated ACA territory infarction were favourable. However, despite good mRS, proximal ACA segment occlusion was associated with the development of distinctive symptoms in ACA territory infarction, which could affect the patients’ dwelling and job status. Acute treatment such as endovascular thrombectomy or administration of intravenous tissue plasminogen activator might be beneficial to patients with proximal occlusion.