Human health and medicine

Hematochezia

Hematochezia, or bright red blood per rectum, is passage of fresh red or maroon blood from the rectum, usually from lower GI bleeding (diverticula, angiodysplasia, neoplasms, colitis, hemorrhoids) but occasionally a brisk upper GI bleed with hemodynamic instability.

Hematocrit

Hematocrit (HCT, packed cell volume, PCV) is the percentage of blood volume made up of red blood cells, measured by centrifugation or calculated by automated Coulter-principle analyzers; typical adult ranges are 41–50% for men and 36–47% for women, used to assess anemia, polycythemia, and dehydration.

Hematology

Hematology is the branch of internal medicine concerned with blood, blood-forming organs, and blood diseases, including anemias, clotting disorders, and blood cancers such as leukemia and lymphoma.

Hematoma

Hematoma: a localized collection of clotted blood outside blood vessels in an organ, tissue, or body space; also called a bruise (contusion) when superficial. Types include subdural, epidural, subungual, and auricular hematomas.

Hematopoietic Stem Cell Mobilization

Hematopoietic stem cell mobilization moves HSCs from bone marrow to blood for apheresis before transplantation, using G-CSF, CXCR4 inhibitors like plerixafor, or cyclophosphamide chemo-mobilization; about 15% of patients mobilize poorly.

Hematoporphyrin Photoradiation

Hematoporphyrin photoradiation, or photodynamic therapy (PDT), is a form of photochemotherapy using visible light applied locally or topically to destroy diseased tissue. Its initial application was described in 1903.

Hematuria

Hematuria, blood in the urine, is gross (visible) or microscopic (≥3 RBC/HPF on urinalysis). Causes range from infection, stones, and BPH to urinary tract cancer; AUA/SUFU guidelines stratify evaluation by malignancy risk.

Heme oxygenase-1 deficiency

Heme oxygenase-1 deficiency (HMOX1D, HO-1 deficiency) is a rare autosomal recessive HMOX1 disorder with asplenia, hemolytic anemia, low bilirubin, hyperinflammation, nephritis, and endothelial injury; first reported 1999.

Hemianopsia

Hemianopsia is the loss of one half of the vertical visual field, usually caused by stroke, brain tumor, or traumatic brain injury, occurring in homonymous or heteronymous forms depending on where the visual pathways are damaged.

Hemiarthroplasty

Hemiarthroplasty is a hip operation that replaces the femoral head and neck with a prosthesis while leaving the socket untouched, used mainly for displaced femoral neck fractures in older adults.

Hemiazygos vein

The hemiazygos vein, also called the inferior hemiazygos vein, is an unpaired left-sided chest vein that drains the lower posterior chest and abdominal wall and empties into the azygos vein.

Hemiballism

Hemiballism (hemiballismus), the most severe form of chorea, causes violent one-sided flinging limb movements from contralateral basal ganglia lesions, classically the subthalamic nucleus though most lesions lie elsewhere; stroke and nonketotic hyperglycemia are leading causes.

Hemibody Irradiation

Hemibody irradiation (HBI), or half-body irradiation, is palliative radiotherapy treating half the body in one field for widespread bone metastases; standard 800 cGy lower and 600 cGy upper doses, about 80% pain response, largely abandoned after the 1990s.

Hemichorea

Hemichorea, also called hemichorea-hemiballismus, is unilateral chorea on one side of the body, classically linked to contralateral subthalamic nucleus lesions but usually caused by stroke or non-ketotic hyperglycemia.

Hemichorea or hemiballismus

Hemichorea or hemiballismus (hemichorea-hemiballism, HCHB), ICD-11 8A01.2: unilateral involuntary choreic or flinging proximal movements from contralateral basal ganglia or subthalamic lesions, most often stroke or nonketotic hyperglycemia; treated with neuroleptics, tetrabenazine, or GPi-DBS.

Hemicolectomy

A hemicolectomy is an operation in which a segment of the colon is removed, most often to treat colon cancer, together with the mesentery and lymph nodes that drain it.

Hemiconvulsion-hemiplegia-epilepsy syndrome

Hemiconvulsion-hemiplegia-epilepsy syndrome (HHE, hemiplegia-hemiconvulsion-epilepsy syndrome) is a rare childhood epilepsy syndrome: febrile hemiclonic status epilepticus, immediate permanent hemiplegia, then drug-resistant focal epilepsy within about 3 years.

Hemicorporectomy

Hemicorporectomy, or translumbar amputation, is an ultra-radical surgery removing the lower half of the body at the lumbar spine, with aorta, vena cava, and spinal cord transection. About 79 cases reported; used for pelvic malignancy, osteomyelitis, and trauma.

Hemicrania continua

Hemicrania continua, a rare indomethacin-responsive trigeminal autonomic cephalalgia, causes continuous strictly unilateral headache with ipsilateral tearing, conjunctival injection, or agitation, diagnosed by ICHD-3 criteria and treated with indomethacin.

Hemidystonia-hemiatrophy syndrome

Hemidystonia-hemiatrophy (HD-HA) syndrome, ORPHA:306741, ICD-10 G24.8: a rare dystonia with hemidystonia and ipsilateral hemiatrophy, usually after perinatal or infantile cerebral injury, stroke, or trauma; fewer than 1 per million.

Hemiepiphysiodesis

Hemiepiphysiodesis is a pediatric orthopedic technique that arrests growth on one side of a growth plate, letting the other side grow to straighten angular limb deformities in children.

Oct 20, 2026

Hemifacial hyperplasia

Hemifacial hyperplasia (hemifacial hypertrophy, facial hemihypertrophy, ORPHA:141145, OMIM 133900) is a rare congenital unilateral overgrowth of facial bone, soft tissue, and teeth, true or partial, isolated or syndromic, treated after growth ceases.

Hemifacial myohyperplasia

Hemifacial myohyperplasia (HFMH) is a rare congenital disorder of unilateral overgrowth of the facial muscles only, without bone or other organ involvement; neonatal onset, prevalence under 1 in 1,000,000, described as a syndrome by Lee et al. in 2001.

Hemifacial spasm

Hemifacial spasm (HFS), also called hemispasme facial, is a movement disorder of unilateral involuntary facial muscle contractions, usually from vascular compression of the facial nerve root exit zone; treated with botulinum toxin and curative microvascular decompression (~90% spasm freedom).

Hemihepatectomy

Hemihepatectomy, including right hemihepatectomy, is a major hepatobiliary operation that removes one half of the liver, right or left, along the Cantlie line, reserved mainly for malignant tumors.

Oct 20, 2026

Hemihyperplasia-multiple lipomatosis syndrome

Hemihyperplasia-multiple lipomatosis syndrome (HHML) is a rare PIK3CA-related overgrowth disorder with asymmetric nonprogressive hemihyperplasia, multiple recurrent lipomas, vascular malformations, and possible embryonal malignancy risk.

Hemilaminectomy

A hemilaminectomy is a spinal decompression procedure that removes bone on one side of a vertebral arch, used in dogs for disc extrusion and in humans for lumbar stenosis.

Hemimandibulectomy

Hemimandibulectomy is the surgical removal of one half of the mandible, performed mainly for oral cancers that invade the jawbone, and usually requiring reconstruction, often with a free fibula flap.

Hemimegalencephaly

Hemimegalencephaly (unilateral megalencephaly) is a rare congenital brain malformation with overgrowth of one cerebral hemisphere, causing infantile drug-resistant epilepsy, hemiparesis, and developmental delay; caused by somatic PI3K-AKT-mTOR mutations and treated with hemispherectomy.