A seemingly normal CT scan after a fall masked a rare stroke affecting both sides of the thalamus, revealed only by unusual eye movements and a subsequent MRI. This case underscores the critical importance of advanced imaging and recognizing subtle neurological signs, even when a patient appears alert.
A 70-year-old man’s fall led to a diagnostic puzzle that highlighted the complexities of stroke recognition. Despite an initial brain CT scan appearing normal, a peculiar and persistent side-to-side eye movement, known as "ping-pong gaze," alerted physicians to a deeper neurological issue. This involuntary, rhythmic oscillation of the eyes, classically observed in comatose individuals, was particularly striking in this patient who remained fully awake and oriented. The anomaly ultimately pointed to a stroke affecting both sides of the thalamus, a vital deep-brain structure, caused by a blockage of the rare artery of Percheron. This case, published in Radiology Case Reports, serves as a crucial reminder that even subtle neurological signs can signal serious underlying pathology, necessitating prompt and comprehensive diagnostic evaluation.
The Subtle Onset of a Deep Brain Stroke
In older adults, a fall can be attributed to a myriad of factors, from simple unsteadiness to more serious medical conditions. Stroke, while a significant concern, is not always the immediate suspect, especially when initial diagnostic imaging provides no clear evidence. This was precisely the situation encountered by the medical team treating a 70-year-old man who presented to the emergency department following a fall. His initial brain computed tomography (CT) scan, a standard rapid diagnostic tool for suspected neurological emergencies, revealed no abnormalities. However, a critical observation was made regarding his eyes: they exhibited a slow, rhythmic, side-to-side movement, a phenomenon termed "ping-pong gaze."
The significance of this finding was amplified by the patient’s overall state. Unlike the typical presentation of ping-pong gaze, which is a hallmark of severe brain injury and loss of consciousness, this individual was awake, alert, and oriented. This discrepancy between the unusual eye movement and the patient’s preserved consciousness presented a diagnostic quandary. The unusual nature of this sign in an awake patient prompted further investigation.
Subsequent magnetic resonance imaging (MRI), a more sensitive imaging modality for detecting early ischemic changes in the brain, provided the crucial diagnosis. The MRI revealed evidence of stroke on both sides of the thalamus, a pair of egg-shaped structures deep within the brain that act as a crucial relay station for sensory and motor signals, as well as playing roles in consciousness, sleep, and alertness. The stroke was attributed to a blockage of the artery of Percheron, a less common anatomical variation where a single small vessel supplies blood to both thalami. This case was documented by Md. Deluwar Hussen and Zareen Tabassum and published in Radiology Case Reports in February 2026.
The Deceptive Normalcy of Early Percheron Strokes
The initial normal appearance of the CT scan in this case is not an anomaly but rather a characteristic feature of strokes involving the artery of Percheron. According to the clinical reference Stroke Manual, CT scans are often unremarkable in the early stages of such strokes. The telltale signs of damage, typically appearing as darker areas on both sides of the thalamus, may only become evident hours or even days later as the stroke evolves and causes swelling and tissue changes. This delay in CT detectability underscores the limitations of this imaging technique in the acute assessment of certain types of strokes.
MRI, with its superior resolution and sensitivity to subtle changes in brain tissue, proved instrumental in this case. The MRI clearly showed hyperintensities, or "bright spots," in the paramedian thalamus on both sides. These bright spots on MRI sequences, such as diffusion-weighted imaging (DWI), are indicative of acute ischemia, meaning a lack of blood flow to the brain tissue. However, even MRI can sometimes appear normal in the very earliest hours of a stroke, emphasizing the need for clinical correlation and, if suspicion remains high, serial imaging.
Blood vessel imaging, such as CT angiography or MR angiography, often adds limited value in directly visualizing the artery of Percheron itself. Due to its small size, this artery is rarely visualized on standard angiography. Therefore, clinicians typically infer the diagnosis of an artery of Percheron stroke from the characteristic pattern of bilateral thalamic damage observed on MRI. In this particular case, however, MR angiography was an exception, revealing a single perforating artery originating from the right posterior cerebral artery. The authors of the report emphasized the critical importance of early MRI and MR angiography in cases where an initial CT scan is negative, especially when clinical signs suggest a potential stroke.
Ping-Pong Gaze: A Sign of Deep Brain Disruption
Ping-pong gaze, a slow, repeating, side-to-side movement of both eyes, is a fascinating and often unsettling neurological sign. In its classic presentation, it is observed in comatose patients. According to a 2023 case report published in Frontiers in Neurology, the eyes in this scenario sweep from one extreme to the other approximately every two seconds. This involuntary eye movement was first briefly described by neurologist C. Miller Fisher in 1967. The authors of the Frontiers report explained that this sign typically occurs in unconscious individuals whose upper brain structures have been functionally disconnected from the midbrain, while the lower brainstem and cerebellum remain largely intact. This disconnection disrupts the normal control of eye movements, leading to the characteristic rhythmic oscillation.
The case of the awake and oriented 70-year-old man is therefore highly unusual. The presence of ping-pong gaze in a patient who is not in a coma is a rare finding, and its association with an artery of Percheron stroke is even more uncommon. The authors of the report specifically described it as an "unusual and uncommon" finding in this context, labeling it a "very rare finding" in their publication’s title. This rarity underscores the diagnostic challenge presented by this patient’s presentation.
Researchers have also identified a faster, "saccadic" form of abnormal eye movement, which may appear in patients with less profound unconsciousness and potentially less extensive brain damage. The exact mechanisms underlying the generation of ping-pong gaze, even in its various forms, are still a subject of ongoing research, but it is generally understood to involve disruptions in the complex neural circuitry that controls eye movements, particularly those originating from or affecting the brainstem and thalamus.
The Artery of Percheron: A Single Vessel, Dual Responsibility
The thalamus, situated deep within the brain, plays a pivotal role in relaying sensory and motor information, regulating consciousness, and influencing memory and emotional processing. In the majority of individuals, each side of the thalamus receives its blood supply from an independent set of small perforating arteries branching off from the posterior cerebral arteries. This dual vascular supply provides a degree of redundancy, meaning that a blockage in one of these small vessels might not necessarily compromise the function of the entire thalamus.
However, in individuals with the artery of Percheron, a significant anatomical variation exists. Instead of separate blood supplies, a single trunk arises from the first segment of one of the posterior cerebral arteries. This solitary vessel then bifurcates, or splits, to supply blood to both the left and right thalami, and often also to a portion of the midbrain. Consequently, a blockage in this single artery of Percheron can lead to simultaneous ischemic damage on both sides of the thalamus, and potentially the midbrain as well.
A narrative review published in August 2026 in Langenbeck’s Archives of Surgery identified a blockage of the artery of Percheron as a rare but significant cause of bilateral thalamic strokes. The authors of this review highlighted three hallmark features commonly associated with this condition: altered consciousness, difficulty with vertical eye movements (up and down), and memory disturbances. Furthermore, they noted the presence of a characteristic "V sign" on MRI in approximately half of the cases involving the midbrain. This "V sign" refers to a specific pattern of signal abnormality that can be observed on MRI, reflecting the vascular territory supplied by the artery of Percheron.
The causes of artery of Percheron occlusion are diverse and can include small-vessel disease (atherosclerosis affecting smaller arteries), large-vessel disease (blockages in major arteries leading to the brain), embolic events (blood clots traveling from the heart or elsewhere in the body), and in some instances, no clear underlying cause can be identified.
The Urgency of Rapid Recognition and Intervention
Strokes affecting the artery of Percheron can present with a wide spectrum of symptoms, often mimicking other neurological conditions. Altered mental status is one of the most consistent features, ranging from mild somnolence and confusion to profound coma. This variability in presentation can make prompt diagnosis challenging. In addition to cognitive changes, patients may experience memory loss, behavioral alterations, and problems with coordination.
The prognosis for individuals who suffer an artery of Percheron stroke is heavily influenced by whether the midbrain is also involved. Strokes confined solely to the thalamus often lead to substantial recovery, although persistent memory and cognitive deficits are not uncommon. However, involvement of the midbrain, which plays a critical role in arousal, attention, and motor control, is associated with a more guarded prognosis. This can result in lasting eye movement abnormalities, slurred speech (dysarthria), weakness, and in some cases, chronic excessive sleepiness.
This case serves as a crucial reminder for both the public and medical professionals that stroke does not always manifest as the classic symptom of sudden one-sided weakness. The Centers for Disease Control and Prevention (CDC) provides a broader list of stroke warning signs, including sudden confusion, sudden trouble seeing in one or both eyes, sudden dizziness, sudden loss of balance or coordination, and sudden trouble walking. The CDC strongly urges individuals to call 911 immediately upon recognizing any of these symptoms and to note the exact time when the symptoms first appeared, as this information is critical for determining appropriate treatment options, such as the administration of thrombolytic medications.
The case of the 70-year-old man underscores a vital lesson for families: an older adult who experiences a fall and subsequently exhibits unusual drowsiness, confusion, or abnormal eye movements warrants immediate and urgent medical evaluation. Even if an initial diagnostic scan appears reassuring, persistent or unusual neurological signs should not be dismissed. Prompt recognition, advanced imaging, and a comprehensive clinical assessment are paramount in ensuring timely diagnosis and intervention for potentially life-altering conditions like stroke.
