Glossary

haemangioendothelioma
malignant tumour originating from the blood vessels
Example / Relevance Pediatrics: haemangioendotheliomas of the liver are very rare congenital tumours that can cause acute heart failure in newborns.

haemangioma
benign neoplasms of blood vessels (sometimes also referred to as blood sponges) mainly in the skin, but also, depending on the type of haemangioma, in other organs; haemangiomas develop in the first few weeks of life or are already present at birth, but usually regress on their own within a few years.

haematocrit (Abrev.: HCT)
the proportion of blood cells in the blood, depending mainly on the concentration of red blood cells (erythrocytes); since red blood cells make up about 99% of the cell components of the blood, the determination of the hematocrit value allows conclusions to be drawn about the proportion of erythrocytes in the blood.
Example / Relevance Pediatrics: the hematocrit is determined as part of the blood count.

haematoma syn. bruising
leakage of blood from injured blood vessels into body tissue or into an existing body cavity; a haematoma can be caused, for example, by an external injury or by a tumour.
Example / Relevance Pediatrics: children/adolescents with a lack of platelets (thrombocytopenia), e.g. in the case of leukaemia or chemotherapy, often develop haematomas, even after minor injuries.

haematopoiesis syn. blood formation
formation of blood cells (blood cells and platelets) from haematopoietic stem cells (blood stem cells) in the bone marrow; blood cells have a limited lifespan, so they need to be renewed regularly.
Example / Relevance Pediatrics: haematopoiesis may be reduced and/or disturbed in cancers affecting the bone marrow (e.g. leukaemias, bone marrow metastases), as well as in non-malignant bone marrow diseases.

haematuria
increased occurrence of red blood cells (erythrocytes) in the urine; medicine distinguishes between two forms of haematuria: in the so-called macrohaematuria, the blood in the urine is clearly visible: the urine appears red or brown in color. Microhaematuria can only be detected by microscopic examination. Haematuria may indicate a disease of the genitourinary system (urinary and genital organs).
Example / Relevance Pediatrics: chemotherapy with certain drugs (e.g. platinum derivatives) or radiotherapy in the area of the kidneys can result in kidney damage with subsequent haematuria.

haemoglobin (Abrev.: Hb)
iron-containing protein in red blood cells (erythrocytes); responsible for the transport of oxygen in the body.
Example / Relevance Pediatrics: in anaemia, haemoglobin levels are reduced.

hamartoma
benign tumour that develops during embryonic development as a result of a malformation of the germ tissue
Example / Relevance Pediatrics: hamartomas can occur anywhere, but do especially in the ovaries, skin, lungs, liver, and brain.

hemihypertrophy syn. hemilateral giant growth
one-sided growth of the body or individual parts of the body (e.g. limbs of one half of the body, half of the head, half of the face); organs can also be affected. In some cases, there are also abnormalities of the skin and teeth as well as hormonal imbalances. Hemihypertrophy can be congenital and present at birth or develop during childhood; however, it can also develop later in life. Hemihypertrophy is observed in the context of certain cancer predisposition syndromes (e.g. Beckwith-Wiedemann syndrome, neurofibromatosis), but can also occur on its own in otherwise normal individuals or as a separate syndrome.
Example / Relevance Pediatrics: hemihypertrophy syndrome – like other giant growth syndromes – can be associated with an increased risk of certain cancers (e.g. with a Wilms tumour).

high-dose chemotherapy
the use of a particularly high dose of cell growth-inhibiting drugs (cytostatics); in the case of cancer, it aims to destroy all malignant cells. Since the haematopoietic system in the bone marrow is also destroyed, the patients own or foreign blood stem cells must then be transferred (autologous or allogeneic stem cell transplantation).

Hirschsprung`s disease syn. congenital megacolon
congenital disease of the large intestine in which nerve cells are missing in part of the colon; the malformation can lead to impaired bowel movements such as severe constipation as well as enlargement of the large intestine (megacolon), bloating (meteorism), vomiting and intestinal obstruction. Inflammatory complications are also possible.

histological
concerning the tissues of the body; in a histological (fine tissue) examination, tissue samples are examined under the microscope after special preparation (preparation of tissue sections and use of certain staining techniques).

histology
study of the tissues of the body
Example / Relevance Pediatrics: histology (or histopathology) plays an important role in the diagnosis of cancer. In a histological (fine tissue) examination, tissue samples are examined microscopically after special preparation (preparation of tissue sections and use of certain staining techniques). In paediatric oncology, exact diagnoses can usually only be made based on histological findings (as well as possibly other laboratory findings).

HIV
abbreviation for "human immunodeficiency virus"; HIV belongs to the retrovirus family. After an incubation period of varying lengths, usually several years, an infection leads to AIDS (acquired immunodeficiency syndrome), an immunodeficiency disease that is currently still incurable.

HLA syn. histocompatibility antigenes
abbreviation for human leukocyte antigen; HLA are protein structures (antigens) on the surface of most body cells that are recognized by T lymphocytes, a subtype of the white blood cells. They serve the immune system to distinguish between "endogenous" and "foreign" structures/substances.
Example / Relevance Pediatrics: histocompatibility antigens are of central importance for the tissue compatibility of transplants; in allogeneic stem cell transplantation, incompatible HLA antigens on the transplanted cells can cause an immunological rejection reaction in the recipient. For this reason, a so-called tissue typing (HLA typing) of both donor and recipient is carried out before each transplant (to ensure that the HLA molecules match as closely as possible).
References: protein - allogeneic stem cell transplantation - immunological - T lymphocytes - antigen - molecule

Hodgkin lymphoma syn. Hodgkin’s lymphoma, Hodgkins disease
malignant disease of the lymphatic system; belongs to the malignant lymphomas and accounts for about 5% of malignant diseases in childhood and adolescence.

hormone
chemical signaling substances (proteins) that are produced in different body glands and have different tasks (for example: thyroid hormone, growth hormone, sex hormones).

Horner`s syndrome syn. Horners triad
combination of signs of a disease in one eye based on eye muscle paralysis of various causes; signs of illness include, for example, the recession of the eyeball into the eye socket (enophthalmus), a narrowing of the pupil (miosis) and drooping of the upper eyelid (ptosis).
Example / Relevance Pediatrics: Horner`s syndrome can occur when the sympathetic trunk is damaged at the level of the cervical spine. This can be the case, for example, with neuroblastoma.

hydrocephalus
medical term for abnormal buildup of cerebrospinal fluid in the cavities (ventricles) in the brain; it is caused by a dilation of the brain’s ventricles due to various causes.
Example / Relevance Pediatrics: A so-called occlusive hydrocephalus (hydrocephalus internus occlusus) can be the result of a drainage impairment of the cerebrospinal fluid, e.g. due to a cerebellar tumour, such as medulloblastoma, blocking the flow. Temporary or permanent drainage of the cerebrospinal fluid may then be necessary.

hyperleukocytosis
severe leukocytosis, i.e. a greatly increased number of white blood cells (leukocytes) in the blood compared to the age-appropriate norm (over 100,000 compared to 5,000 to 8,000 leukocytes per microlitre of blood).
Example / Relevance Pediatrics: hyperleukocytosis, for example, occurs in some patients with acute leukaemia and has an adverse effect on the chances of recovery.

hypocellular
reduced number of (blood-forming) haematopoietic cells in the bone marrow, which may affect one or more haematopoietic cell lines; this results in a reduced number of certain blood cells (erythrocytopenia, thrombocytopenia and/or leukocytopenia) or even all blood cells in the blood (pancytopenia).

hypothalamus
part of the diencephalon and supreme control organ of the endocrine system; the hypothalamus controls numerous vegetative body functions (e.g. blood pressure and heart rate) and is the overarching center of homeostasis. It controls, among other things, the wake-sleep rhythm, appetite and thirst, body temperature and sex drive, and it processes the sensation of pain and temperature. It also controls the pituitary gland and stimulates it to release hormones.