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Thiel-Behnke corneal dystrophy
Thiel-Behnke corneal dystrophy (TBCD, honeycomb corneal dystrophy, CDB2) is a rare autosomal dominant TGFBI (5q31, Arg555Gln) corneal dystrophy causing recurrent erosions, honeycomb subepithelial opacities, and progressive vision loss, treated with PTK.
Thigh
Thigh: the lower-limb segment between hip and knee, built around the femur. Its anterior, medial, and posterior muscle compartments (quadriceps, adductors, hamstrings) extend and flex the hip and knee, adduct the leg, and are prone to strains in athletes.
Third heart sound
Third heart sound (S3, ventricular gallop): low-frequency early-diastolic sound 120–180 ms after S2 from rapid filling deceleration; normal under ~40, otherwise marks heart failure, with 51% sensitivity and 90% specificity for reduced ejection fraction.
Thoracic aorta
Thoracic aorta: the chest portion of the aorta, divided into ascending aorta, arch, and descending segment. Covers anatomy, embryology, aneurysm, acute aortic syndromes, imaging, and TEVAR versus open repair.
Thoracic aortic aneurysm
A thoracic aortic aneurysm is an abnormal widening of the aorta in the chest, usually symptomless and found on imaging, with rupture and dissection as the main dangers.
Thoracic diaphragm
Thoracic diaphragm: the dome-shaped musculofibrous partition between chest and abdomen, the primary mammalian inspiratory muscle, with T8, T10, and T12 openings and sternal, costal, and crural regions.
Thoracic duct
Thoracic duct: the body's largest lymphatic vessel, 38–45 cm, draining ~75% of lymph into the left venous angle; highly variable anatomy, key in chylothorax and neck surgery.
Thoracic outlet syndrome due to cervical rib
Thoracic outlet syndrome due to cervical rib (ICD-11 8B91.1): neurovascular compression at the thoracic outlet caused by an extra rib from C7, found in 1.1% of healthy people but 29.5% of TOS patients.
Thoracic vertebrae
Thoracic vertebrae (T1–T12, vertebrae thoracicae) are the twelve middle-spine bones bearing costal facets for rib articulation, forming the kyphotic, least-mobile thoracic segment, with atypical T1, T11, and T12 and transitional T12 anatomy.
Thoracic wall
Thoracic wall (chest wall): the musculoskeletal enclosure of the thorax, bounded by sternum, 12 rib pairs, thoracic vertebrae, and diaphragm, with intercostal muscles, neurovascular bundles, and roles in protection and breathing.
Thorax
Thorax: the body region between neck and abdomen, enclosed by the rib cage (12 rib pairs, sternum, 12 thoracic vertebrae), containing heart and lungs in mediastinum and pleural cavities; key breathing and trauma anatomy.
Thromboangiitis obliterans
Thromboangiitis obliterans, also called Buerger disease, is a non-atherosclerotic inflammatory disorder that blocks small and medium arteries of the hands and feet, almost exclusively in tobacco users.
Thrombophlebitis
Thrombophlebitis, also called phlebitis or superficial vein thrombosis, is vein inflammation caused by a blood clot, usually in leg veins near the skin; distinguished from deep vein thrombosis by ultrasound and treated with heat, NSAIDs, or anticoagulants.
Thumb
Thumb (pollex): the first digit, with two phalanges and a saddle-shaped trapeziometacarpal joint enabling opposition and pinch. Covers anatomy, evolution, basal joint arthritis, fractures, and reconstruction.
Thygeson superficial punctate keratitis
Thygeson superficial punctate keratitis (TSPK), also called Thygeson's superficial punctate keratopathy, is a rare chronic bilateral corneal epitheliopathy with recurrent gray-white intraepithelial opacities, unknown cause, HLA-DR3 association, and corticosteroid-responsive flares.
Thymectomy
Thymectomy is surgical removal of the thymus gland, performed in myasthenia gravis to improve weakness or remove a thymoma (about 10% of MG patients). The 2016 MGTX randomized trial confirmed benefit plus prednisone; MuSK-antibody MG is excluded.
Thymic cyst
Thymic cyst: fluid-filled sac within thymic tissue in the mediastinum or neck; congenital (unilocular) or acquired (multilocular, linked to inflammation or tumors). Benign, often asymptomatic; CT attenuation can mimic solid masses, MRI clarifies, surgery or surveillance.
Thymic hyperplasia
Thymic hyperplasia: benign enlargement or lymphoid follicular proliferation of the thymus, including true, rebound, follicular, and LESA-like types; linked to myasthenia gravis and Graves disease, distinguished from thymoma by chemical shift MRI.
Thymic involution
Thymic involution is the age-related atrophy of the thymus, replacing T-cell-producing epithelial tissue with fat from early life onward, reducing naive T cell output and raising infection, cancer, and autoimmune risk; partially reversible experimentally but no approved therapy.
Thymopentin
Thymopentin (TP-5), Arg-Lys-Asp-Val-Tyr, a synthetic pentapeptide matching amino acids 32-36 of thymopoietin; immunomodulator enhancing T-cell production, studied in HIV, tuberculosis, and eczema, never FDA-approved.
Thymosin
Thymosin: family of thymus-derived polypeptide hormones named in 1966 by Goldstein and White. Key members are thymosin alpha-1 (Zadaxin, sepsis and hepatitis studies, not FDA-approved) and thymosin beta-4 (actin-binding, wound healing, WADA-prohibited).
Thymulin
Thymulin, formerly known as FTS, is a zinc-dependent nonapeptide hormone produced by thymic epithelial cells that promotes T cell differentiation, discovered by French immunologists in the 1970s.
Thymus
Thymus: bilobed primary lymphoid organ in the superior mediastinum where T cells mature and undergo selection; undergoes involution from puberty; linked to myasthenia gravis, DiGeorge syndrome, and thymectomy.
Thymus histology
Thymus histology is the microscopic structure of the thymus, a two-lobed lymphoepithelial organ above the heart, organized into a thymocyte-packed cortex and a paler medulla containing Hassall's corpuscles.
Thymus transplantation
Thymus transplantation (cultured thymus tissue implantation, CTTI, RETHYMIC) treats congenital athymia by implanting cultured donor thymus slices into quadriceps muscle; FDA approved October 8, 2021, available at Duke and Great Ormond Street Hospital, 77% one-year survival.
Thyroid
Thyroid: butterfly-shaped endocrine gland in the neck producing T4 and T3 under TSH control; depends on iodine; hypothyroidism affects about 4.6% of Americans age 12 and older.
Thyroid hormones
Thyroid hormones: T4 (thyroxine) and T3 (triiodothyronine), iodine-containing hormones from the thyroid gland regulating metabolism, growth, and brain development, activated locally by deiodinases and replaced clinically with levothyroxine.
Thyroid-stimulating hormone
Thyroid-stimulating hormone (TSH, thyrotropin) is an anterior pituitary glycoprotein hormone that drives thyroid T4/T3 secretion via the TSH receptor; its log-linear feedback makes it the frontline thyroid test, with pregnancy and biotin interference as key caveats.
Thyrotroph
Thyrotroph (thyrotrope, TSH cell): anterior pituitary cell producing thyroid-stimulating hormone. Rarest pituitary endocrine cell (~5%), Pit-1/GATA2 lineage, stimulated by TRH, suppressed by T3 feedback.
Thyrotropin-releasing hormone
Thyrotropin-releasing hormone (TRH), also known as thyrotropin-releasing factor or protirelin, is a hypothalamic tripeptide that stimulates TSH and prolactin release and was first isolated in 1969.