Moyamoya disease (MMD) was first described in 1957 as angiographic hypogenesis of the bilateral internal carotid arteries. However, it was formally recognized as a pathological entity by Suzuki and Takaku et al., around 1969. MMD is a chronic, progressive cerebrovascular disorder characterized by stenosis of the terminal portion of the bilateral internal carotid arteries, leading to the formation of an abnormal capillary-like vascular network at the base of the skull. This vascular pattern resembles a “puff of smoke”, which in Japanese is termed “moyamoya” [1,2].

Moyamoya disease is the most common genetic pattern found in the R4810K polymorphism in the RNF213 ring-finger protein gene on chromosome 17q25.3; this genetic susceptibility factor is highly significant in East Asian populations [2]. Recent genetic studies have identified mutations in BRCC3/MTCP1 and GUCY1A3 as potential contributors to the pathogenesis of MMD, along with its association with certain monogenic syndromes that may underlie this angiopathy. Epidemiological data indicate that MMD has the highest prevalence in Japan, with rates ranging from 3 to 16 per 100,000 individuals annually. Research further suggests a female predominance in the affected population [3].

The Japanese Committee for Moyamoya Disease Research, established in 1974, has accumulated extensive experience in diagnosing and managing MMD, spanning over 45 years. The anatomical classification of vascular lesions dates back to 1978 [4].

The European Stroke Organization (ESO) has developed standardized guidelines for Moyamoya angiopathy, recommending direct bypass surgery in adults presenting with hemorrhagic events. Surgical intervention is typically recommended within one to two weeks following a stroke event. Additionally, some experts advocate for the use of antiplatelet therapy in non-hemorrhagic MMD to reduce the risk of embolic strokes [5].

An 18-month-old child presented to the emergency department after several hours of jerky movements. These episodes, lasting up to 5 minutes, included brief staring spells, muscle weakness, rigidity, drooling, and behavioral changes. The seizures recurred after 30 minutes, at which point he exhibited right-sided hemiparesis and a Glasgow Coma Scale (GCS) score of 12. He was subsequently transferred to Morozoskaya Children’s Hospital, where he received anticonvulsant therapy within the first hour. His medical history revealed that the seizures began after surgery for congenital heart disease. His history also included congenital Trisomy 21 (Down syndrome), multiple ventricular septal defects (perimembranous and muscular), an accessory left superior vena cava draining into the coronary sinus, tricuspid valve insufficiency, and a history of posterior cerebral artery ligation. He had previously undergone repair of a ventricular septal defect with a PTFE patch and muscular suture. Upon arrival at Morozoskaya Children’s Hospital, he was administered intravenous diazepam (0.3 mL of 5 mg/solution), which successfully stopped the seizures. His Glasgow Coma Scale (GCS) score on admission to Morozoskaya Children’s Hospital, in Moscow Russia, decreased to 9 to 24 hours, with persistent 2/5 right hemiparesis; magnetic resonance imaging (MRI) revealed findings suggestive of Moyamoya disease (MMD) (Figure 1). Cerebral angiography at 72 hours confirmed this diagnosis. Surgical treatment, a direct extracranial-intracranial (EC-IC) revascularization, was performed the following day. This involved a frontoparietotemporal osteoplastic craniotomy, followed by a microsurgical anastomosis between the parietal branch of the left superficial temporal artery (STA) and the M4 segment of the left middle cerebral artery (MCA) (STA-MCA), supplemented with encephaloduromyoperiosynangiosis. The direct bypass was chosen to provide immediate Revascularization. The surgery lasted 4.5 hours (Figure 2). Postoperative course: Twenty-four hours after the surgery, while in the Intensive Care Unit (ICU), the patient developed hydrocephalus secondary to ventricular dilation, necessitating a surgical reintervention. Short-term outcome: Postoperative changes: Included Enlargement of the left meningeal spaces, gas bubbles, and accumulation of CSF fluid were observed. The decision was reintervention; 350 mL of cerebrospinal fluid (CSF) was manually removed with a syringe and collected in an emesis basin or kidney tray to reduce intracranial pressure. Concurrently, an external ventricular drain (EVD) was placed intraoperatively to drain CSF and prevent further ventricular expansion and hydrocephalus recurrence. Conclusion: The patient remained in the ICU, receiving conservative treatment including antibiotics, with particular attention to comfort, hydration, fever management, and ongoing monitoring for hydrocephalus (Figure 3). Seven days later, neurological signs improved significantly, with cessation of seizures and restoration of muscle tone and reflexes. The patient was transferred to the ward with right hemiparesis improved to 3/5, and was discharged one month later. A follow-up plan was implemented by the neurology and neurosurgery departments one month after discharge. This follow-up confirmed the positive postoperative result, with the patient remaining hemodynamically stable. See Figures 1-4.

Moyamoya disease causes secondary ischemic stroke due to chronic stenosis of the cerebrovascular system and impaired cerebral perfusion. Revascularization surgery is the most effective treatment for establishing cerebral circulation, with direct bypass surgery particularly efficacious for optimizing perfusion of the middle cerebral artery (MCA). STA-MCA bypass is the standard direct revascularization operation to increase cerebral flow in patients with MMD [6].

This report describes an STA-MCA procedure performed on an 18-month-old child. Performing such a procedure at this young age is a complex technical decision, justified by the urgent need for immediate revascularization. Direct bypass offers advantages in critical scenarios by immediately restoring blood flow, preventing recurrent infarcts, and halting the ischemic cascade.

Neurocognitive outcomes in Moyamoya patients have been of increasing interest. Studies on Moyamoya disease have revealed that affected patients exhibit significantly lower nonverbal IQ scores, impaired fine motor function, and overall cognitive impairment on preoperative testing [7]. Despite early diagnosis, surgical revascularization remains the optimal method to reestablish cerebral perfusion and avoid subsequent ischemic injury [8] (Table 1).

The operation in this case involved direct revascularization through an extracranial-to-intracranial bypass, connecting the superficial temporal artery to the middle cerebral artery. Microsurgical techniques were employed to increase precision and improve cerebral perfusion. Postoperative imaging showed stabilization of cerebral circulation, marked by reduced brain density loss in the frontoparietal region of the left hemisphere and improved peripheral cerebral circulation. However, a persistent area of reduced density was still observed in the left frontal lobe, with less active peripheral circulation compared to previous imaging studies.

Postoperative changes included an expansion of the membrane spaces in the operated left hemisphere to a peak of 11 mm, accompanied by gas bubbles and blood-density inclusions along the sulci and gyri. Cerebrospinal fluid accumulation was observed along the interhemispheric fissure, in the left parietal region, and in the right hemisphere. Additionally, blood accumulation was noted near the tentorium of the cerebellum on the right.

Soft-tissue changes at the operative site consisted of infiltration, edema, and a gas-filled fluid collection measuring 115 mm in length and 17 mm in thickness. The trepanation defect was adequately covered by a bone flap, which incorporated periosteum and temporalis muscle along its edge. The dural defect in the frontal region was closed using a DuraGen substitute.