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Anisocoria
Anisocoria, unequal pupil sizes, is a common sign ranging from benign physiologic anisocoria (up to 20% of people, ≤1 mm) to Horner syndrome, Adie pupil, third nerve palsy, and pharmacologic causes, evaluated by light/dark comparison and drug tests.
Ankle
The ankle, or talocrural joint, connects the foot to the lower leg where the tibia, fibula, and talus meet, allowing walking through dorsiflexion and plantarflexion.
Ankle jerk reflex
Ankle jerk reflex (Achilles tendon reflex, ankle reflex): S1 deep tendon reflex producing triceps surae contraction and plantar flexion; tested by dorsiflexion and tendon tap, lost in S1 radiculopathy and diabetic neuropathy.
Ankle–brachial pressure index
Ankle–brachial pressure index (ABI, ABPI): ratio of ankle to brachial systolic blood pressure, a non-invasive bedside test; ABI ≤0.90 diagnoses lower limb peripheral artery disease and low values predict cardiovascular risk.
Ankylosis
Ankylosis: pathological stiffening and fusion of a joint, bony or fibrous, from disease, trauma, or surgery; distinct from surgical arthrodesis; central to ankylosing spondylitis and TMJ ankylosis.
Anna Bågenholm
Anna Bågenholm (born 1970) is a Swedish radiologist in Tromsø who survived 1999's skiing accident under ice with the lowest recorded survived body temperature, 13.7 °C.
Anomalies of pupillary function
Anomalies of pupillary function (ICD-11 LA11.62; pupillary disorder, anomaly of pupil function) is a group of conditions in which iris muscles fail to regulate light entering the eye, covering miosis, mydriasis, hippus, iridoplegia, and myotonic pupil.
Anomalous aortic origin of a coronary artery
Anomalous aortic origin of a coronary artery (AAOCA, ACAOS) is a congenital defect where a coronary artery arises from the wrong aortic sinus; found in up to 1% of people, a leading cause of sudden cardiac death in young athletes, managed by risk stratification and unroofing surgery.
Anomalous aortic origin of the left coronary artery
AAOLCA, anomalous aortic origin of the left coronary artery from the right aortic sinus, a rare congenital coronary anomaly; rarer than the right-coronary form but carrying higher risk of ischemia and sudden cardiac death in young athletes, treated by unroofing surgery.
Anomalous left coronary artery from the pulmonary artery
ALCAPA, or Bland-White-Garland syndrome, is a rare congenital defect where the left coronary artery arises from the pulmonary artery, causing coronary steal, infant heart failure, and over 90% first-year mortality without surgery.
Anomalous origin of coronary artery from the pulmonary artery
Anomalous origin of coronary artery from the pulmonary artery (ACAPA; ALCAPA, Bland-White-Garland syndrome, or ARCAPA): a rare congenital defect causing coronary steal, infant heart failure, about 90% first-year mortality untreated, and surgical reimplantation as the preferred repair.
Anomalous pulmonary venous connection
Anomalous pulmonary venous connection, also called anomalous pulmonary venous return, is a congenital heart defect in which pulmonary veins drain into the systemic venous circulation instead of the left atrium.
Anoxic-ischaemic encephalopathy
Anoxic-ischaemic encephalopathy (ICD-11 8B24.0), also called hypoxic-ischemic encephalopathy, is brain injury from combined cerebral hypoxia and ischemia, occurring after adult cardiac arrest and neonatal asphyxia, treated with cooling in newborns.
Anterior cerebral artery
Anterior cerebral artery (ACA), artery of the circle of Willis supplying medial frontal and parietal cortex and corpus callosum; segments A1-A5, variants include azygous ACA and persistent primitive olfactory artery, associated with aneurysms.
Anterior cruciate ligament
The anterior cruciate ligament (ACL) is one of two cruciate ligaments of the knee, joining femur to tibia and stabilizing the joint against excessive movement.
Anterior horn motor neuron
Anterior horn motor neuron (anterior horn cell, ventral horn motor neuron): a lower motor neuron of the spinal cord's anterior horn, in Rexed lamina IX, with alpha and gamma types, that innervates skeletal muscle via acetylcholine at the neuromuscular junction as the final common pathway; targeted in ALS, SMA, and polio.
Anterior pituitary
Anterior pituitary (adenohypophysis): front lobe of the pituitary gland in the sella turcica; five cell types secrete GH, prolactin, ACTH, TSH, FSH, and LH under hypothalamic portal control.
Anthropometry
Anthropometry (from Greek anthropo, metron) is the systematic measurement of human body dimensions: height, weight, circumferences, skinfolds, BMI. Founded by Quetelet (Anthropometrie, 1871); includes Bertillon's forensic bertillonage, WHO child growth standards, and ISO 7250 design data.
Antiarrhythmic agent
Antiarrhythmic agents are drugs for abnormal heart rhythms, grouped by the Vaughan Williams classes I–IV (sodium channel, beta-blocker, potassium channel, calcium channel blockers), extended in 2018 with classes 0 and V–VII; CAST showed class Ic drugs raise post-infarction mortality.
Antihypertensive and Lipid Lowering Treatment to Prevent Heart Attack Trial
The Antihypertensive and Lipid Lowering Treatment to Prevent Heart Attack Trial (ALLHAT) was a major US National Heart, Lung, and Blood Institute trial testing newer blood pressure drugs against a diuretic from 1994.
Anus
The anus is the terminal 3-4 cm opening of the large intestine, guarded by involuntary internal and voluntary external sphincters, divided by the pectinate line, and affected by conditions such as hemorrhoids, fissures, fistulas, and HPV-related anal cancer.
Aorta
The aorta is the body's largest elastic artery, running from the left ventricle through five segments to the iliac bifurcation; coverage spans normal diameters, Windkessel physiology, aneurysm and dissection thresholds, and endovascular repair.
Aortic arch
The aortic arch, or arch of the aorta, is the curved segment of the aorta between its ascending and descending portions, supplying blood to the head, neck, and arms.
Aortic arches
Aortic arches: embryonic pharyngeal arch arteries (six pairs from the aortic sac) and the adult aortic arch; typical branching in ~78-81%, bovine arch 13.6%, ARSA about 1%.
Aortic bifurcation syndrome
Aortic bifurcation syndrome, or Leriche syndrome, is atherosclerotic occlusion of the distal abdominal aorta and iliac arteries, causing buttock-thigh claudication, absent femoral pulses, and impotence; first described by René Leriche in 1923.
Aortic dissection
Aortic dissection: an intimal tear splits the aortic media, creating a false lumen; Stanford type A (ascending) needs emergency surgery with 1–2% mortality per hour untreated, type B managed medically or by TEVAR.
Aortic intramural hematoma
An aortic intramural hematoma (IMH) is bleeding contained within the middle muscular layer of the aortic wall, without an intimal flap, and it can progress to dissection or rupture.
Aortic regurgitation
Aortic regurgitation, also called aortic insufficiency, is the diastolic leakage of blood from the aorta back into the left ventricle through a failing aortic valve.
Aortic rupture
Aortic rupture: full-thickness tear of the aorta, usually from aneurysm rupture (rAAA) or dissection. Pooled rAAA mortality 81%; endovascular repair mortality 24.5% vs 44.4% open; risk rises with aneurysm size.
Aortic valve
Aortic valve: the three-cusp semilunar valve between the left ventricle and aorta. Covers anatomy, embryology, bicuspid valve, stenosis and regurgitation criteria, and SAVR, TAVI, and repair options.