The treatment of stroke patients with large vessel occlusion (LVO) has completely changed after five randomized controlled trials demonstrated the superiority of endovascular thrombectomy (ET) over medical management within the first 6 hours of symptoms [3,4,8,10,13].

The importance of extending the therapeutic window for stroke has been known since 2008 [9]. In 2018, the DAWN [11] and DEFUSE-3 trials [2] demonstrated the effectiveness of ET 6-24 hours from the time last known well (TLKW) in selected patients with mismatch between the clinical deficit severity and infarct core volume.

The type of collateral circulation in each patient can lead to either a large or small ischemic core. Patients in whom a large ischemic core is observed, have a “faster progressor” type; those with a small core have a “slow progressor” type, in which good collaterals are maintained [9]. The type of collateral circulation and consequently the rate of progression can influence the volume of ischemic core and the effectiveness of ET in patients beyond the conventional time window.

There are case series [7] and case reports [1,14] showing good outcomes in patients treated beyond the 24-hour limits of the DAWN trial.

The aim of this article is to report the case of a patient who underwent ET 52 hours after the onset of symptoms, who evolved with significant neurological improvement, despite a possible hyperperfusion-like syndrome. We also conducted a brief literature review on the topic.

A 68-year-old female previously modified Rankin Scale 0 developed mild aphasia with an unknown TLKW; her daughter first observed this in the morning, while talking on the phone with the patient. Seven hours after that, the daughter visited the patient at home; the mild aphasia persisted and so they went to the hospital.

The NIHSS (National Institutes of Health Stroke Scale) score at admission was 4. Computed tomography (CT) angiography revealed a left M1 occlusion (Fig. 1). Because of the low NIHSS score and almost 7 hours after the ictus, no venous thrombolysis or interventional treatment was proposed. At that time, aspirin was prescribed.

Fifty-one hours after the TLKW, the patient had an NIHSS score of 11; a perfusion magnetic resonance imaging (MRI) revealed an ischemic core volume of 8 ml with a large mismatch ratio observed, and therefore, an ET was proposed (Fig. 2).

Groin puncture occurred 52 hours after the TLKW; subsequently a direct-aspiration first-pass technique (ADAPT) was used and one pass resulted in a thrombolysis in cerebral infarction scale (TICI) grade 3 recanalization.

The day after the procedure, an NIHSS score of 16 was observed; no hemorrhagic signals were detected by CT.

Five days after the procedure, the patient had an NIHSS score of 3 with a mild dysarthria and partial facial palsy. She was discharged to another hospital.

The patient is followed up on an outpatient basis. In the 6-month evaluation, the patient still presents with an NIHSS score of 2, being capable of self-care (Modified Rankin Scale 2).

This kind of case raises a huge discussion about whether patients can be treated outside of the standard therapeutic window and whether the type of collateral circulation can extend this window. It is already known that ＜30% [6] of patients with LVO have a “slow progressor” type and can benefit substantially from ET after 8 hours. This was demonstrated in the DAWN [11] and DEFUSE-3 [2] trials.

Our case presents that some patients might have a very slow progressor type, which we name “turtle” progressor type. These patients could possibly benefit from ET beyond the DAWN trial criteria (＞24 hours) in highly selected cases. This progressor type might exist where there is an exceptional capacity to sustain collateral blood flow, and where the ischemic core does not become enlarged, protecting the penumbra area.

Another interesting point which is seen in this case is a major worsening the day after treatment (NIHSS score of 11 to 16) without hemorrhagic transformation despite successful endovascular treatment (TICI 3). In addition to the Contrast-induced encephalopathy already described by some authors [5], it could be that patients with the slow progressor type, and in our case the “turtle” progressor type, may suffer a cerebral hyperperfusion-like syndrome when a TICI grade 3 recanalization is achieved after LVO. Because recanalization changes the low-pressure cerebral flow in the microcirculation (collateral flow) to a high-pressure flow, a hyperperfusion-like syndrome that we call “collateral syndrome” could occur. This event needs to be evaluated in other patients with the collateral profile of slow progressor and “turtle” progressor to analyze the reproducibility of this kind of “collateral syndrome”.

This is a rare case demonstrating a very late thrombectomy 52 hours after the TLKW with a good recovery observed 5 days after the procedure.

In some cases, there appears to be a direct relationship between some types of collateral circulation (slow progressor and “turtle” progressor) and extension of the treatment window. Patients with these progressor types can experience a hyperperfusion-like syndrome (“collateral syndrome”) after the recanalization of an LVO, which can lead to clinical worsening in the 48 hours immediately after the ET. However, further studies are needed in order to evaluate the reproducibility of this hypothetical syndrome.