2,701 articles
Pyogenic granuloma
Pyogenic granuloma, or lobular capillary hemangioma, is a benign vascular tumor of skin and mucosa that grows rapidly, bleeds easily, and is linked to trauma, pregnancy, hormones, and drugs.
Pyramidal cell
Pyramidal cell (pyramidal neuron): excitatory projection neuron of the cerebral cortex and hippocampus with pyramid-shaped soma, apical dendrite toward the pial surface, spiny dendrites, and a base-originating axon; the most common cortical neuron.
Pyramidal tracts
Pyramidal tracts: cortical motor fiber systems (corticospinal and corticobulbar tracts) passing through the medullary pyramids; about 75-90% decussate, controlling voluntary movement, with lesions causing contralateral weakness.
Quadrants and regions of abdomen
Quadrants and regions of abdomen: two topographic systems dividing the abdominal surface. Four quadrants (RUQ, LUQ, RLQ, LLQ) from planes through the umbilicus at L3-L4; nine regions from midclavicular, subcostal, and transtubercular planes.
Quadratus lumborum muscle
Quadratus lumborum: posterior abdominal wall muscle between the iliac crest, 12th rib, and L1-L4 transverse processes; weak lumbar stabilizer, inspiration accessory, and target of the quadratus lumborum block.
Quadriceps
Quadriceps femoris, the four-headed anterior thigh muscle group (rectus femoris, vastus medialis, lateralis, intermedius), the primary knee extensor innervated by the femoral nerve L2-L4, central to patellofemoral pain rehabilitation.
Quinpirole
Quinpirole (LY 171555) is a pyrazoloquinoline compound acting as a full agonist at dopamine D2 and D3 receptors, used in research as the reference full agonist.
RACS study
RACS study (Risk in Acute Coronary Syndrome; Risk Markers in the Acute Coronary Syndromes, NCT00521976): single-center prospective Norwegian cohort of 871 chest-pain patients at Stavanger University Hospital, 2002-2003, studying risk markers, 24-month mortality, and recurrent troponin-T events.
Radial artery
The radial artery runs from the elbow down the thumb side of the forearm to the hand, and is the standard site for feeling a pulse.
Radial glial cell
Radial glial cell (RGC), embryonic neural stem cell spanning ventricle to pia; primary progenitor generating cortical neurons and glia and scaffold for neuronal migration; transforms into astrocytes after neurogenesis.
Radial nerve
Radial nerve: C5–T1 terminal branch of the brachial plexus posterior cord, supplying arm and forearm extensors and dorsal hand sensation; injuries cause wrist drop, Saturday night palsy, and Wartenberg's syndrome.
Radiation myelitis
Radiation myelitis, or radiation-induced myelopathy, is spinal cord injury from radiotherapy, spanning transient Lhermitte's-sign myelopathy and chronic progressive myelitis; risk is dose- and fractionation-dependent, rising sharply above 50 Gy.
Radiation-induced valvular heart disease
Radiation-induced valvular heart disease is calcification and dysfunction of heart valves, usually aortic and mitral, caused by chest radiation therapy, appearing a median 23 years later.
Radiculopathy
Radiculopathy, also called radiculitis or nerve root disorder, is pain, numbness, tingling, and weakness from a compressed spinal nerve root; types are cervical, thoracic, and lumbar, most often caused by disc herniation.
Radiofrequency ablation
Radiofrequency ablation (RFA): catheter-based cardiac procedure using RF-heated tips to destroy arrhythmic tissue; standard for AF pulmonary vein isolation since Haissaguerre's 1998 work, with ~4.5% major complication rate.
Radionuclide ventriculography
Radionuclide ventriculography (RNV, MUGA, gated blood pool scan, ERNA) is a nuclear medicine test measuring ventricular ejection fraction with Tc-99m labeled red cells and ECG-gated gamma camera imaging, by first-pass or equilibrium methods; once the main nuclear cardiology technique, now used when echo or MRI are unsuitable.
Radius (bone)
Radius: the lateral, thumb-side long bone of the forearm, articulating with humerus, ulna, and carpal bones; about 25 cm in adults; enables pronation and supination; distal radius fractures are common.
Ralph W. Gerard Prize in Neuroscience
Ralph W. Gerard Prize in Neuroscience: the Society for Neuroscience's highest honor, a lifetime-achievement award named for SfN founder Ralph Waldo Gerard (1900–1974); recent recipients include Joshua Sanes (2025) and Nora D. Volkow (2024).
Randy Gardner sleep deprivation experiment
The Randy Gardner sleep deprivation experiment kept 17-year-old Randy Gardner of San Diego awake for a record 264 hours in 1963–1964, as a school science fair project.
Rapid eye movement sleep
Rapid eye movement (REM) sleep, also called paradoxical sleep, is a sleep state with activated EEG, rapid eye movements, and muscle atonia, discovered by Aserinsky and Kleitman in 1953, generated by a pontine flip-flop switch, and linked to vivid dreaming and REM behavior disorder.
Rapid eye movement sleep behavior disorder
REM sleep behaviour disorder (RBD, REM sleep behavior disorder) is a parasomnia with loss of REM atonia and dream enactment; about 80% of isolated cases convert to synucleinopathy within 10 years; treated with clonazepam, melatonin, pramipexole, or rivastigmine.
RASA1-related capillary malformation-arteriovenous malformation
RASA1-related capillary malformation-arteriovenous malformation (CM-AVM1, OMIM 608354) is a rare autosomal dominant RASopathy causing multiple pink capillary malformations with a pale halo, with AVMs or AVFs in about a quarter of carriers.
Rasagiline
Rasagiline (Azilect) is a selective, irreversible MAO-B inhibitor drug approved for Parkinson's disease, first approved in Israel and Europe in 2005 and by the US FDA in 2006.
Reactive plasmacytic hyperplasia
Reactive plasmacytic hyperplasia (reactive plasmacytosis), ICD-11 2B32.1, is a benign polytypic plasma cell increase in blood, marrow, or nodes caused by infection, AITL, drugs, malignancy, or autoimmunity, distinct from plasmacytoma.
REALITY trial (NCT02850107)
REALITY (NCT02850107), the VIVA REALITY study, was a single-arm trial of directional atherectomy before paclitaxel drug-coated balloon angioplasty in 102 patients with long, calcified femoropopliteal lesions: 76.7% 12-month patency, 8.8% provisional stenting.
Recovery of Function
Recovery of function (MeSH D020127) is the partial or complete return of normal physiologic activity after disease or trauma, distinguished from compensation, driven by neuroplasticity, and pursued mainly through stroke rehabilitation with a 2-3 month intensive-therapy window.
Recovery position
Recovery position: side-lying first aid posture (lateral recumbent, HAINES variant) for unresponsive but breathing people to keep the airway open and prevent aspiration; ILCOR weakly recommends it, evidence is observational only.
Rectal arterial supply and portocaval anastomosis
The rectum is supplied by three arteries, the superior, middle, and inferior rectal arteries, whose veins link the portal and systemic systems in a portocaval anastomosis.
Rectum
The rectum (Latin intestinum rectum, straight intestine) is the 12-15 cm distal segment of the large intestine between the sigmoid colon and anal canal, a distensible reservoir for feces with superior, middle, and inferior rectal arterial supply.
Rectus abdominis muscle
Rectus abdominis, the paired "six pack" muscle of the anterior abdominal wall, runs from the pubic crest and symphysis to the xiphoid process and costal cartilages 5-7, flexes the trunk, and is segmented by tendinous inscriptions.