A Case Report: The Myxomatous Mystery

Introduction: Primary cardiac tumors are rare with an incidence rate of 1.38 new cases per 100,000 individuals per year. Of these tumors, 75% are benign in origin and the most common type is a myxoma with a frequency of over 50%. Myxomas most commonly arise from the left atrium followed by the right atrium. Clinical presentation of a myxoma varies depending on the location, size, and shape of the tumor. For example, a patient diagnosed with a myxoma may have constitutional symptoms, cardiovascular symptoms, pulmonary symptoms etc. or may be entirely asymptomatic. Since there is no specific symptoms presented by patients with a myxoma, physicians often face challenges in diagnosing. Case Presentation: A 72-year-old female with a past medical history of hypertension presented to the Emergency Department (ED) with progressive dyspnea on exertion of 1-week duration. She reported chest tightness, orthopnea, and paroxysmal nocturnal dyspnea. She denied experiencing similar symptoms in the past. Vital signs were unremarkable except for her blood pressure which was 178/103 mm Hg. Pertinent physical exam findings included jugular venous distension, a S3 heart sound, and bibasilar rales. Laboratory tests were ordered and all were unremarkable, including her troponin I and BNP levels. ECG was significant for T wave inversion in the inferior leads. Chest x-ray and CT were ordered and showed diffuse ground glass opacities throughout both lungs, bilateral pleural effusions, and mild cardiomegaly, as well as dilation of the main pulmonary artery. Lasix was given as patient appeared to be volume overloaded which resulted in brisk diuresis and relief of symptoms. At this point, an acute exacerbation of left-sided heart failure was suspected and a transthoracic echocardiogram (TTE) was ordered. TTE revealed a large ovoid mobile echodense mass. The mass was 5.1 cm x 2.9 cm and attached to the lower half of the interatrial septum on the left atrium and moved in and out of the left ventricular inflow. This finding was most consistent with a left atrial myxoma and the patient was then transferred to a medical center capable of resecting the myxoma. The patient tolerated the myxoma excision well and was discharged to cardiac rehabilitation. The surgical pathology report confirmed cardiac myxoma with central hemorrhage. Discussion: In the setting of predisposed hypertension, we suspect that the large size and mobile nature of the left atrial myxoma caused functional partial obstruction of the mitral valve, leading to secondary valvular heart disease and eventually progressive left-sided heart failure. Despite the rarity of the disease, myxomas as well as other cardiac tumors should always be included in the differential diagnosis when a patient presents with symptoms suspected of an acute exacerbation of heart failure. Echocardiogram is the diagnostic modality of choice to utilize when a myxoma is suspected

Contrast Adaptation Contributes to Contrast-Invariance of Orientation Tuning of Primate V1 Cells

BACKGROUND: Studies in rodents and carnivores have shown that orientation tuning width of single neurons does not change when stimulus contrast is modified. However, in these studies, stimuli were presented for a relatively long duration (e. g., 4 seconds), making it possible that contrast adaptation contributed to contrast-invariance of orientation tuning. Our first purpose was to determine, in marmoset area V1, whether orientation tuning is still contrast-invariant with the stimulation duration is comparable to that of a visual fixation. METHODOLOGY/PRINCIPAL FINDINGS: We performed extracellular recordings and examined orientation tuning of single-units using static sine-wave gratings that were flashed for 200 msec. Sixteen orientations and three contrast levels, representing low, medium and high values in the range of effective contrasts for each neuron, were randomly intermixed. Contrast adaptation being a slow phenomenon, cells did not have enough time to adapt to each contrast individually. With this stimulation protocol, we found that the tuning width obtained at intermediate contrast was reduced to 89% (median), and that at low contrast to 76%, of that obtained at high contrast. Therefore, when probed with briefly flashed stimuli, orientation tuning is not contrast-invariant in marmoset V1. Our second purpose was to determine whether contrast adaptation contributes to contrast-invariance of orientation tuning. Stationary gratings were presented, as previously, for 200 msec with randomly varying orientations, but the contrast was kept constant within stimulation blocks lasting >20 sec, allowing for adaptation to the single contrast in use. In these conditions, tuning widths obtained at low contrast were still significantly less than at high contrast (median 85%). However, tuning widths obtained with medium and high contrast stimuli no longer differed significantly. CONCLUSIONS/SIGNIFICANCE: Orientation tuning does not appear to be contrast-invariant when briefly flashed stimuli vary in both contrast and orientation, but contrast adaptation partially restores contrast-invariance of orientation tuning