Thinking about the other left lower quadrant
The patient is a 74 year-old African-American female with a history of hypertension, coronary artery disease status post drug-eluting stent ×1, former cigarette smoker, and iron deficiency anemia presenting with left-sided vision loss. Patient states that approximately two days ago she woke up with painless peripheral vision loss of her left eye only. She describes it as darkness in the lateral portion of her left eye. She reports that her vision returned to baseline throughout that day; only to return when she awoke the next morning. Since that time she endorses persistent vision loss in the left periphery. She denies blurry vision, eye pain, headaches, recent trauma, flashes, and floaters. Furthermore, she also denies dizziness, numbness weakness, dysarthria, dysphagia, fever, chills nausea, vomiting, chest pain, shortness of breath, and palpitations. She reports adherence to her antihypertensive and anti-platelet medications.
Past Medical History: Hypertension, NSTEMI status post drug eluding stent x1, Osteoarthritis
Medications: Aspirin, atorvastatin, chlorthalidone, clopidigrel, metoprolol, benazepril, pantoprazole
T 36.4 HR 74 RR 16 BP 167/109 O2 Sat 96% on RA
The patient’s exam revealed a well appearing, elderly African-American female who appeared alert, oriented and in no acute distress. Neurologic exam revealed intact extraocular movements and her pupils were equal and reactive bilaterally. Confrontational visual field exam was remarkable for bilateral left lower quadrantanopia. Visual acuity was 20/40 bilaterally. Cranial nerves III - XII were intact. She ambulated with a cane and gait was at baseline. Strength and sensation was intact in all extremities. There was no cerebellar dysmetria or truncal ataxia. National Institute of Health Stroke Scale (NIHSS) was 1. Her pulmonary exam was unremarkable. Her cardiovascular exam revealed a regular rhythm, normal S1/S2 without murmur or gallops and she had 2+ peripheral pulses bilaterally.
EKG: normal sinus rhythm, unchanged as compared to previous EKG
CT Head Noncontrast: Age-indeterminate infarction involving the parasagittal right occipital lobe.
CTA Head & Neck: Diminished enhancement of distal cortical branches of the right posterior cerebral artery in the right parieto-occipital region corresponding to the region of suspected infarct on noncontrast CT.
Neurology was consulted in the Emergency Department. Given the patient’s low NIHSS and symptom duration of >48 hours, the decision was made not to give tissue plasminogen activator (tPA). The patient was admitted to the neurology service and underwent MRI of the brain (Figure 1) that showed an acute ischemic infract in the right occipital regions, moderate to severe chronic microvascular disease and remote right cerebellar and left basal ganglia infarcts. The etiology of her stroke was thought to be from thromboembolic phenomena based on her diffuse ischemic disease on imaging. Given her history of NSTEMI, neurology considered a cardiac source of the emboli. As such, the patient underwent a cardiac MRI that revealed no evidence of mural thrombus or vegetations. Throughout her hospital stay she had no improvement in her vision. She was, however, able to ambulate without problems. Occupational therapy evaluated the patient and recommended assistance at home and outpatient therapy for visual training. She was ultimately discharged home on hospital day two with continuation of all her home medications and instructions to follow up with neurology as an outpatient.
Acute, Painless, Unilateral Vision Loss
The differential diagnosis for acute-onset vision loss is broad. However, there are several key features from the history that can be useful for the Emergency Physician in determining initial workup and management. Specifically, this patient experienced acute, painless, “unilateral” vision loss. The most common pathologies causing this presentation are listed in Table 1.
Neuro-ophthalmologic vision loss is defined as vision loss that is not readily explained by an abnormality on physical exam of the eye for which a cause distal to the retina is suspected. The lesion can be located anywhere from the optic nerve to the occipital cortex, and will cause a specific visual field defect based on location. While a slit lamp exam and ultrasonography may be helpful in the work up of retinal and vitreous pathologies, these modalities will not be of much value in diagnosing the majority of neuro-ophthalmologic lesions.
An accurate history and directed physical exam is key in the ED workup of acute-onset vision loss. Confrontational visual field testing, or Donder’s Test, can be performed in seconds as part of the bedside exam.  The examiner should assume a position directly across from the patient at arm’s length, so that their eyes align on the same horizontal and vertical plane. The patient should cover their right eye with their right hand and vice versa when testing the opposite eye. With the examiner seated directly across from the patient, the patient should direct their gaze to the corresponding eye of the examiner. Starting outside the usual 180 degree visual field, the examiner should move the hand slowly to a more central position until the patient confirms visualization of the target. Once visualization is confirmed, use this at the starting point for stationary testing. To perform stationary testing, the examiner holds up a certain number of fingers peripherally, equidistant between the examiner and the patient. The patient is asked to correctly identify the number of fingers. The visual fields of both eyes overlap; therefore, each eye should be tested independently and all four quadrants (superior, inferior, left, right) should be tested.
In the above case, while the patient only recognized loss of vision in her left eye, confrontational visual field testing revealed vision loss in the left lower quadrant of both eyes, termed homonymous left lower quadrantanopia. Identification of that deficit helped to rule out non-neuro-ophthalmalogic causes of vision loss such as retinal ischemia, retinal or vitreous detachment, and vitreous hemorrhage leading to an appropriate workup and the ultimate diagnosis.
The visual cortex is located in the occipital lobe, as depicted in Figure 2. The left hemispheric visual cortex receives signals from the right visual field, and the right hemispheric visual cortex receives signals from the left visual field via the optic radiations. The inferior division of the optic radiation, or Meyer’s Loop, contains input from the superior visual field quadrants, and travels around the inferior horns of the lateral ventricles in the temporal lobe. The superior division, or Baum’s Loop, contains input from the inferior visual field quadrants, and travels in the parietal lobe and has a much more direct path to the visual cortex. If a lesion is isolated to one division in one hemisphere only, the resulting visual defect is called quadrantanopia, which implies that only the respective superior or inferior quadrant of the visual field is affected. However, a lesion in the visual cortex itself can also cause a quadrantanopia if isolated to the area where the optic radiation terminates. The subtle differences in these presentations are only detectable by perimetry testing, which cannot be done at the bedside.
At the conclusion of the history and exam, the lesion in our patient was isolated to the right hemispheric superior optic radiation passing through the parietal lobe or in the visual cortex itself. A retrospective study in JAMA Neurology found that the location and frequency of lesions causing inferior quadrantanopia were most commonly the occipital lobe (76%), followed by the parietal lobe (22%) and temporal lobe (2%).  The study also found that if the lesion is in the parietal lobe, i.e. the optic radiations, then it will most often have associated parietal lobe deficits such as paresthesia, hemiparesis, neglect and aphasia. Lesions in the occipital lobe do not commonly have localizing symptoms on physical exam.
The ED workup of vision loss should be based on the history and exam and tailored appropriately. If cerebral infarction i suspected, as in our patient, and if the patient is presenting within a three-hour window, a non-contrasted CT head and CTA head and neck should be obtained emergently to determine eligibility for IV-TPA. The stroke team should also be contacted.
Additional studies should include CBC, renal panel for creatinine and glucose specifically, and coagulation studies. An EKG should be obtained, as the most common cause of a cardioembolic stroke is atrial fibrillation. Other sources of cardiogenic embolism include a mural thrombus on a hypokinetic wall segment, endocarditis, prosthetic heart valve thrombosis, rheumatic heart disease, and paradoxical embolism via a patent foramen ovale or atrial septal defect. Cardioembolic sources account for an estimated 20-25% of ischemic stroke. These pathologies may be ruled out by an echocardiogram as an inpatient. Cardiac MRI is the gold standard for characterization of cardiac sources of embolism, although it has never proven to be superior to echo for detection of vegetations, and should only be utilized when there is still high suspicion for cardiac source and echocardiogram is nondiagnositic.  Thromboembolism from large or small vessel atherosclerotic disease is thought to be responsible for approximately 45% of ischemic stroke and is best visualized by CTA of the head and neck or with carotid ultrasonography
The administration of intravenous (IV) tissue plasminogen activator (tPA) is dependent on the time of presentation, the contraindications present and the degree of neurologic deficits. Most practitioners would not administer tPA for isolated quadrantanopia as in our patient even if within the 3-hour window; however, a thorough discussion of the risks/benefits with the patient and family should be had. If the patient is outside of the IV-tPA window, but less than 6 hours from symptom onset, there should be consideration of intrarterial (IA) tPA administration if a larger vessel occlusion is found. The AHA/ASA recommends IA-tPA in select patients with MCA occlusion within 6 hour of symptom onset but no recommendation is made for IA-tPA in posterior circulation stroke, including basilar artery occlusion.  The American College of Chest Physicians recommandations, however, include patients with acute occlusions of any proximal cerebral blood vessel (e.g. ICA, MCA, basilar artery, vertebral artery) under the assumption that the pathophysiology and accessibility were believed to be similar for all major intracranial arterial locations.  In regards to mechanical clot retrieval, per the AHA/ASA guidelines, patients with an ischemic stroke caused by a proximal large artery occlusion in the anterior circulation are candidates for mechanical thrombectomy if presenting in less than 6 hours and without other contraindications. Additionally, although the benefits are uncertain and evidence is lacking, the use of stent retrievers may be reasonable for carefully selected patients with acute ischemic stroke who have occlusion of vertebral arteries, basilar artery, or posterior cerebral arteries.  Our patient was unfortunately outside of the window for any of these acute interventions and the anatomical location of her lesion would not have been amenable to thrombectomy regardless. She will most likely have persistent visual field deficits as evidenced by her neuroimaging.
In regards to long-term treatment, patients with a history of noncardioembolic ischemic stroke should continue aspirin, clopidogrel, or aspirin/extended release dipyridamole. Additional contributing comorbidities such as hypertension, diabetes, hyperlipidema, obesity and tobacco use should also be managed meticulously to reduce the risk of future CVA.
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