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Lazarus sign
Lazarus sign: complex spinally mediated arm-flexion movement in brain-dead patients, named by Ropper 1984, occurring in about 2% during apnea testing or ventilator withdrawal; does not invalidate brain-death diagnosis.
Lazarus syndrome
Lazarus syndrome, or autoresuscitation, is the delayed unassisted return of spontaneous circulation minutes after CPR is stopped and death declared; about 76 reported cases since 1982, mechanisms include auto-PEEP and delayed drug effects.
Left anterior descending artery
Left anterior descending artery (LAD), anterior interventricular branch of the left coronary artery; supplies 50-60% of the left ventricle; its occlusion causes anterior STEMI, the highest-risk coronary occlusion.
Left anterior fascicular block
Left anterior fascicular block (LAFB, left anterior hemiblock) is a conduction delay in the anterior fascicle of the left bundle branch, causing marked left axis deviation on ECG; common in the elderly and a marker of cardiac risk.
Left atrial appendage occlusion
Left atrial appendage occlusion (LAAO), also called left atrial appendage closure, seals the left atrial appendage to prevent stroke in atrial fibrillation; Watchman and Amulet devices show noninferiority to anticoagulation with less non-procedural bleeding.
Left superior caval vein
Left superior caval vein (persistent left superior vena cava, PLSVC): the most common thoracic venous anomaly, a left-sided SVC draining via the coronary sinus, present in about 0.6% of people and up to 10% of congenital heart disease patients.
Leptomeningeal carcinomatosis
Leptomeningeal carcinomatosis, also called leptomeningeal metastasis or neoplastic meningitis, is spread of cancer cells within the leptomeninges and subarachnoid space, affecting about 5% of cancer patients, most often from breast, lung cancer, or melanoma, diagnosed by CSF cytology and MRI.
Lesion of common peroneal nerve
Lesion of common peroneal nerve (peroneal nerve palsy, common fibular nerve dysfunction, ICD-10 G57.3): injury to the sciatic-nerve branch at the fibular neck causing foot drop, eversion weakness, and sensory loss; graded by Sunderland classification.
Lesion of plantar nerve
Lesion of plantar nerve (ICD-11 8C11.6): damage to the medial or lateral plantar nerves, tibial nerve branches below the tarsal tunnel. Causes include entrapment, trauma, and surgery; presents with burning pain, paresthesias, jogger's foot, Morton's neuroma.
Lesion of radial nerve
Lesion of radial nerve (ICD-10 G56.3, ICD-11 8C10.2), also called radial neuropathy or radial nerve palsy: injury to the radial nerve causing wrist drop, most often from humeral fracture or compression, usually recovering with splinting.
Lesion of ulnar nerve
Lesion of ulnar nerve (ICD-11 8C10.1): ulnar neuropathy, usually cubital tunnel syndrome at the elbow or Guyon canal syndrome at the wrist; second most common upper-limb entrapment neuropathy, treated conservatively or surgically.
Levator ani
Levator ani, the main pelvic diaphragm muscle made of puborectalis, pubococcygeus, and iliococcygeus; supports pelvic viscera, maintains continence, innervated mainly by S3-S4, injured in 13-36% of vaginal deliveries.
Levo-Transposition of the great arteries
Levo-transposition of the great arteries (L-TGA, ccTGA) is a rare congenital heart defect with double discordance leaving the right ventricle systemic; over 80% have associated lesions, and heart block, tricuspid regurgitation, and ventricular failure dominate management.
Levobunolol
Levobunolol (levobunolol hydrochloride ophthalmic solution) is a noncardioselective topical beta-blocker, distinct from timolol and betaxolol, used once or twice daily to lower intraocular pressure in open-angle glaucoma and ocular hypertension.
Lewy body
Lewy body: intraneuronal aggregate of misfolded alpha-synuclein protein, discovered by Friedrich Lewy in 1912. Defines Parkinson's disease, dementia with Lewy bodies, and Parkinson disease dementia; definitive diagnosis requires autopsy.
Leydig cell
Leydig cells, or interstitial cells of the testes, are steroid-producing cells in the testis that make testosterone and were named after Franz Leydig, who identified them in 1850.
Lie detection
Lie detection, best known through the polygraph or lie detector, infers deception from physiological responses. Invented by Marston, Larson, and Keeler in the 1910s-1920s, it is above chance but scientifically weak, excluded from most courts, and used mainly for security screening.
Ligamentous laxity
Ligamentous laxity, or joint hypermobility, is looseness of ligaments allowing joints to move beyond normal range; assessed by the Beighton score, linked to collagen genes, EDS, ACL injury, and disc herniation.
Ligamentum arteriosum
The ligamentum arteriosum, also called the Ligament of Botallo, is the fibrous remnant of the fetal ductus arteriosus, running from the pulmonary trunk to the aortic arch.
Lightheadedness
Lightheadedness, also called light-headedness or presyncopal dizziness, is a vague faint or floating sensation, one of four dizziness types, caused by reduced cerebral blood flow (orthostatic hypotension, arrhythmia), hyperventilation, anxiety, or medications.
Limb (anatomy)
Limb (anatomy): paired upper and lower human appendages of the appendicular skeleton, 30 bones each, attached by pectoral and pelvic girdles; upper limb for mobility, lower for weight bearing.
Limb overgrowth
Limb overgrowth, ICD-11 LB97, is abnormal enlargement of a limb or digit seen in macrodactyly, hemihyperplasia, Klippel-Trenaunay syndrome, and PIK3CA-related overgrowth spectrum (PROS), caused by somatic mosaic PIK3CA pathway mutations.
Limbic system
Limbic system: forebrain structures common to all mammals (amygdala, hippocampus, hypothalamus, cingulate gyrus, septal nuclei, anterior thalamus) implicated in emotion, memory, and survival behaviors; term coined by MacLean in 1952 from Broca's 1878 limbic lobe and Papez's 1937 circuit.
Lingual papillae
Lingual papillae (papillae linguales) are mucosal projections on the tongue's dorsal surface, of four types: filiform, fungiform, foliate, and circumvallate; only filiform lack taste buds, and fungiform are ectoderm-derived while circumvallate and foliate are endoderm-derived.
Lissencephaly
Lissencephaly (smooth brain), including agyria, pachygyria, and subcortical band heterotopia, is a cortical malformation from defective neuronal migration at 12-24 weeks gestation, mainly caused by PAFAH1B1 (LIS1) and DCX mutations, with epilepsy and short life expectancy.
List of animals by number of neurons
List of animals by number of neurons: ranked neuron counts, from fruit fly (166,000) and octopus (500 million) to human (86 billion) and African elephant (257 billion), with counting methods and limits as intelligence predictors.
List of bones of the human skeleton
Bones of the human skeleton: conventionally 206 adult bones, 80 axial and 126 appendicular, excluding sesamoid, sutural, and accessory bones; newborns have 275 to 300 before fusion.
List of human anatomical regions
Human anatomical regions: named body areas (head, neck, thorax, abdomen, pelvis, limbs) defined by palpable landmarks; subdivided into quadrants and nine abdominal regions, standardized by Terminologia Anatomica and ICD-11 surface anatomy terms.
List of human positions
List of human positions: named body orientations such as anatomical, supine, prone, lateral, Fowler's, Trendelenburg, lithotomy, and tripod, used as references in anatomy, imaging, nursing, and surgery.
List of nerves of the human body
List of nerves of the human body: the 12 pairs of cranial nerves (olfactory through hypoglossal) and 31 pairs of spinal nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal), plus major named peripheral nerves such as the sciatic, median, and vagus.