H1N1 influenza is a strain of influenza that notably resulted in a pandemic in 2009.
It is type of influenza A virus of swine origin.
There can be a wide spectrum of clinical syndromes with patient's ranging from being asymptomatic to having fulminating viral p...
The habenula is part of the epithalamus and receives input from the brain via the stria medullaris. It outputs to many midbrain areas involved in releasing neuromodulators, such as dopamine, norepinephrine, and serotonin.
The habenula was traditionally divided into lateral (limbic) and medial (...
A habitual miscarriage is the term given when a woman has had more than 3 miscarriages and it affects approximately 1-2% of women.
Many causes are identified.
mullerian duct anomalies
acquired uterine causes
uterine adhesion bands
Haemangioblastomas are tumours of vascular origin and occur both sporadically and in patients with von Hippel Lindau (vHL). They are WHO grade I tumours that can occur in the central nervous system or elsewhere in the body, including kidneys, liver, and pancreas.
These tumours generally present...
A haemangioendothelioma is a tumour derived from blood vessels.
Sub types dependent on location include
haemangioendothelioma of liver
This article is intended to be the general article on haemagi...
Haemangiomas are benign tumours of vascular origin usually seen in early childhood, divided into
Unfortunately, the term haemangioma has been widely misused to apply to many non-neoplastic vascular malformations, particularly the com...
Haemangiopericytoma is a term formerly used to describe a continuum of mesenchymal tumours with elevated cellularity found throughout the body in soft tissue and bone. After many years of controversy, haemangiopericytomas have been shown to not only share histological features similar to solitar...
Haemangiopericytomas of the spleen are a very rare vascular neoplasm with only a few case reports available at the time of writing.
Splenic haemangiopericytomas are typically asymptomatic or can result in splenomegaly.
These are a soft tissue vascular neoplasm...
Haemarthosis is haemorrhage into a joint space and can be regarded as a subtype of a joint effusion.
Trauma is by far the most common cause of a haemarthosis. Other causes include bleeding disorders, neurological deficits, arthritis, tumours and vascular damage.
Lipohaemarthrosis is a result o...
Haematocolpos is a term given to a blood-filled dilated vagina due to menstrual blood in the setting of an anatomical obstruction, usually an imperforate hymen. In this condition, there is no distention of the uterine cavity, c.f. haematometrocolpos.
Patients may present...
The haematocrit effect with fluid-fluid levels is the result by layering of heavier cellular elements of blood located dependent to liquid supernatant may be seen on CT or MRI. It is most frequently seen in the setting of anticoagulation therapy or coagulopathy.
signal flare phenomenon
A haematometrium refers to a uterus filled with blood.
pyometrium: uterus filled with pus
haematometrocolpos: uterus and vagina filled with blood
hydrometrium: uterus filled with fluid
Haematometrocolpos refers to a blood-filled distended uterus and vagina usually due to an anatomical mechanical obstruction precluding the evacuation of the menstrual blood.
The estimated incidence in teenagers is at ~1 in 1000-2000 5.
imperforate hymen: in ~2...
Haematomyelia refers to the presence of intramedullary haemorrhage or haematoma within the spinal cord. This is distinct from extramedullary haemorrhage, such as that seen in epidural haematomas.
Although this can occur in the setting of trauma, the term is generally used to signify non-traumat...
Haematopoietic stem cell transplantation (HSCT) is a relative common procedure used to treat a wide spectrum of conditions 1,2:
lymphoproliferative disorders, e.g. lymphoma, multiple myeloma (most common indication)
solid tumours, e.g. neuroblastoma, Ewing sarcoma, extragonadal germ...
Abdominal complications of haematopoietic stem cell transplantation can occur early (0-100 days) or late (>100 days) post transplant.
bacterial infections, e.g. pseudomembranous colitis
fungal infections, often affecting the oesophagus or as hepatic/splenic microabscesse...
A haematosalpinx refers to intraluminal blood within the Fallopian tube (often dilated).
tubal ectopic pregnancy: common cause 1
endometriosis: common cause 5
pelvic inflammatory disease
fallopian tube torsion
Haematospermia refers to the presence of blood in semen or ejaculatory fluid. It is a symptom that can cause great anxiety to patients despite commonly being of benign aetiology.
urogenital infections including sexually transmitted disease
commonest cause in <40 years of ...
Haematuria occurs when blood enters the urinary collecting system. There are many aetiologies for haematuria, and they range from benign and transient to gravely concerning. Haematuria can derive from the kidneys, ureters, bladder, prostate (in men), or urethra. Imaging can often be useful to de...
Haematuria in a child is evaluated differently than in an adult in two main respects:
there is a lower likelihood of a malignancy (renal or bladder) causing the haematuria
preference is given to nonionizing radiation
Haematuria can be considered in three main forms:
Haemobilia refers to the presence of blood in the biliary tree.
The classical clinical triad, only seen in ~50% of cases, consists of:
melaena (i.e. upper gastrointestinal bleeding)
iatrogenic: surgical or percutaneous pro...
Haemochromatosis is an iron overload disorder characterised by a progressive increase in total body iron stores and deposition of iron in some non-reticuloendothelial system (RES) body organs which results in some instances in organ dysfunction.
This article focus on the general principles of h...
Cardiac involvement in haemochromatosis typically occurs with primary haemochromatosis, as the organ is usually spared in the secondary form of the disease.
Cardiac involvement occurs in approximately 15-20% of the patients with haemochromatosis.
Pancreatic manifestations of haemochromatosis typically occur with primary haemochromatosis, as the organ is usually spared in the secondary form of the disease.
Iron deposition can occur in the pancreas with primary hemochromatosis. Pancreatic involvement is uncommon in patients wi...
Haemochromatosis is a systemic disease which affects many organs systems (see the main hemochromatosis article), including the joints, characterised by haemosiderin and calcium pyrophosphate deposition resulting in:
chondrocalcinosis: particularly knees and triangular fibrocartilage
An acquired arm arteriovenous fistula (AVF) creation is a procedure performed for haemodialysis access in those with end stage renal failure. It connects and artery to a vein in the vein. This can either be a native connection or a connection using a PTFE (polytetrafluoroethylene) graft.
A hemoglobinopathy is a genetic disorder which alters the structure of hemoglobin 1. The result is reduced oxygen carrying capacity of the blood to the tissues.
Types of hemoglobinopathies include the following:
Sickle cell disease (Hb S)
Sickle cell trait (HB AS)
Haemolytic anaemia is a form of anaemia where red blood cells (RBCs) are destroyed either intravascularly or extravascularly.
The patient presents with anaemia and jaundice. Diagnosis is based on several laboratory parameters 1:
increased unconjugated bi...
Haemolytic disease of the newborn (HDN) results when maternal antibodies attack the fetal red blood cells, leading to a haemolytic anaemia and accumulation of bilirubin in the fetus or newborn. It can affect the newborn to varying degrees of severity. When the condition occurs in utero, the term...
Haemolytic uraemic syndrome (HUS) is a multisystem thrombotic microangiopathic disease characterised by the triad of renal failure, haemolytic anaemia and thrombocytopenia. It is the most common cause of renal failure in infancy and childhood requiring dialysis.
There are two forms of this syn...
Haemopericardium refers to the presence of blood within the pericardial cavity, i.e. a sanguineous pericardial effusion. If enough blood enters the pericardial cavity, then a potentially fatal cardiac tamponade can occur.
There is a very long list of causes 1,4 but some o...
Haemoperitoneum is the presence of blood within the peritoneal cavity.
penetrating or non-penetrating abdominal trauma (often with associated organ injury) 1
ruptured ectopic pregnancy
ovarian cyst rupture
aneurysm or pseudoaneurysm rupture
Haemophagocytic lymphohistiocytosis (HLH) is a nonmalignant disorder of immune regulation characterised by overproduction of cytokines and diminished immune surveillance. It may affect multiple organs.
It typically affects infants and children 5.
The condition can be p...
Haemophilia is an inherited bleeding disorder which is X-linked recessive and therefore occurs almost exclusively in males. There are two subtypes - haemophilia A (80%) and haemophilia B (20%).
The incidence of haemophilia A is around 1 in 5000 male births, and the incidence of h...
Haemophilic arthropathy refers to permanent joint disease occurring in haemophilia sufferers as a long-term consequence of repeated haemarthrosis. Around 50% of patients with haemophilia will develop a severe arthropathy.
Haemophilia is an x-linked recessive disease affecting mal...
Haemophilic pseudotumour is a rare complication of haemophilia consisting of a progressive cystic swelling of muscle and/or bone, occurring in less than 2% of haemophiliacs.
It is reported in 1-2% of haemophiliacs patients.
Most develop in the muscles of the pelvis a...
Haemopneumothorax is a term given when there is concurrent presence of a haemothorax and well as a pneumothorax. It is a variant of a hydropneumothorax.
Approximately 5% of patients with pneumothorax will have concomitant haemothorax 6
It is typically seen in the sett...
Haemoptysis refers to coughing out blood. Generally, it appears bright red in colour as opposed to blood from gastrointestinal tract which appears dark red. It is considered an alarming sign of a serious underlying aetiology.
Massive haemoptysis is referred to as expectoration of >...
Haemorrhage exclusion sign can be a useful MRI finding following prostate biopsy.
The normal prostate produces high concentrations of citrate, which among other properties, acts as an anticoagulant 1. As tumour cells are dysfunctional, they will produce lower levels of citrate than t...
Haemorrhagic cholecystitis refers to an inflammatory process of the gallbladder, complicated by haemorrhage into the lumen.
The presenting features may mimic non-haemorrhagic acute cholecystitis, with right upper quadrant pain being a dominant feature. If the blood is pa...
Haemorrhagic corpus luteal cysts result from bleeding into corpus luteal cysts.
Commonly described findings include
complex adnexal mass
adnexal thick walled cystic lesion with lace like strands
adnexal thick walled cystic lesion with low-level echoes withi...
Haemorrhagic infarct or haemorrhagic transformation of an infarct is seen to occur secondary to the breakdown of the lamina of the microvessels.
Intracerebral haemorrhage (ICH) may overlap with a haemorrhagic infarct and hence needs to be differentiated as the line of treatment will vary.
Haemorrhagic intracranial metastases are considered to represent between 3-14% of all cerebral metastases (c.f. 1-3% of gliomas are haemorrhagic).
These classically originate from:
melanoma: melanoma metastases to brain
renal cell carcinoma
thyroid carcinoma: papillary carci...
Various types of brain tumours may cause haemorrhage. Increased tumour vascularisation with dilated, thin-walled vessels and tumour necrosis are the most important mechanisms of haemorrhage. The list includes:
choroid plexus carc...
A mnemonic for primary malignancies responsible for haemorrhagic metastases is:
MR CT BB
M: melanoma: metastatic melanoma to brain
R: renal cell carcinoma
T: thyroid carcinoma, teratoma
B: bronchogenic carcinoma
B: breast carcinoma
Haemorrhagic ovarian cysts (HOCs) usually result from haemorrhage into a corpus luteum or other functional cyst. Radiographic features are variable depending on the age of the haemorrhage. They typically resolve within eight weeks.
Patients may present with sudden-onset ...
Haemorrhagic pancreatitis is a possible uncommon complication that can occur with pancreatitis and is characterised by bleeding within or around the pancreas. It is usually considered a late sequela of acute pancreatitis.
Haemorrhage can occur in patients with severe necrotising panc...
Haemorrhagic pneumonia refers to a descriptive term for a pneumonia (infective - inflammatory consolidation of the lung) when is complicated by pulmonary haemorrhage. It can be localised or diffuse to varying degrees dependant on the extent of involvement +/- aetiological agent.
Haemorrhagic pulmonary metastases are those which tend to be complicated by pulmonary haemorrhage within them, resulting in characeristic imaging appearances. Metastases of some tumour histologies are more likely to haemorrhage -- knowledge of this can help refine the differential diagnoses.
Haemorrhagic transformation is a complication of cerebral ischaemic infarction and can significantly worsen prognosis.
It should be noted that the term haemorrhagic transformation is a little variably used and collectively refers to two different processes, which have different inc...
The haemosiderin cap sign refers to an MR imaging feature in some spinal tumours where a cap of T2 hypointense haemosiderin is above and/or below the tumour due to previous haemorrhage.
It is most often associated with spinal cord ependymomas, being seen in 20-33% of these cases 1. The sign, h...
Haemosiderosis is a general term referring to accumulation of haemosiderin, which particularly occurs in the reticuloendothelial system (RES) and does not cause organ damage.
Some causes include:
mainly depositional siderosis in RES
if >40 units transfused: t...
Haemosuccus pancreaticus, also known as pseudohaemobilia or haemoductal pancreatitis, is defined as upper gastrointestinal tract haemorrhage originating from the pancreatic duct into the duodenum via the ampulla of Vater, or major pancreatic papilla.
male:female ratio is 7:1
Haemothorax literally means blood within the chest, is a term usually used to describe a pleural effusion due to accumulation of blood. If a haemothorax occurs concurrently with a pneumothorax it is then termed a haemopneumothorax.
A tension haemothorax refers to haemothorax that results from ...
The Haggitt level is a histopathological term used for describing the degree of infiltration from a malignant polypoidal lesion.
Levels of invasion
0: carcinoma in situ or intramucosal carcinoma
1: invasion of the submucosa, but limited to the head of the polyp
2: invasion extending into the...
Haglund deformity, also known as a pump bump or Bauer bump or Mulholland deformity, is defined as bony enlargement formed at posterosuperior aspect of calcaneum. This deformity leads to retrocalcaneal bursitis.
It may result secondary to chronic pressure of rigid shoes.
Haglund syndrome refers to the triad (Haglund's triad) of
insertional Achilles tendinopathy
Haglund deformity (i.e. posterosuperior calcaneal exostosis)
This results in pain at the back of the heel. It is associated with calcaneal spurs, and the wearing of high heels ...
The hair on end sign refers to a radiographic appearance of the diploic space of the skull vault which results from a thickening of trabeculae as the diploic space expands. These trabeculae are perpendicular in orientation, interspersed by radiolucent marrow hyperplasia along the skull vault.
The so-called hairy pleural plaque, are a manifestation of asbestos related disease. They arises from the visceral pleura, typically from an interlobar fissure. The hairiness stems from short radially oriented linear regions of fibrosis extending from the plaque into the adjacent lung parenchyma...
Hajdu-Cheney syndrome was first described as cranioskeletal dysplasia 1 in 1948. It is a very rare connective tissue disorder with only 50 cases reported in the literature 2.
It is mostly diagnosed in adulthood or adolescence with the presence of a positive family history...
Physical half life time (Tp)
The time interval required for an amount of certain radioactive nuclei to decay to its half of original value.
Biological half life time (Tb)
The time interval required for the body to eliminate 50% of any substance by normal routes of elimination: metabolic turn...
Half value layer (HVL) is the width of a material required to reduce the air kerma of a x-ray or gamma-ray to half its original value. This applies for narrow beam geometry only as broad-beam geometry will experience a large degree of scatter, which will underestimate the degree of attenuation. ...
Halitosis refers to the symptom of foul oral odour, commonly termed "bad breath", that patients can present with, usually to dental services.
It is thought to be caused by the presence of volatile sulphur compounds that are produced by bacteria. Although the underlying cause can be s...
Haller cells are also known as infraorbital ethmoidal air cells or maxilloethmoidal cells. They are extramural ethmoidal air cells that extend into the inferomedial orbital floor and are present in ~20% (range 2-45%) of patients, depending on their exact definition 1-3.
In most instances they a...
Hallux rigidus (osteoarthrosis with restricted motion) is the second most common disabling deformity of the first metatarsophalangeal joint after hallux valgus.
It is most commonly seen in middle-aged patients, but can develop during adolescence. Unlike a hallux valgus, males appe...
The hallux sesamoid bones are paired, dual ossicles of the foot. They function as a fulcrum to increase the leverage of both flexor hallucis brevis and longus.
The hallux sesamoids are ovoid-shaped ossicles. There is a medial (tibial) and lateral (fibular) hallux sesamoid and ar...
A hallux valgus is fixed abduction of the first metatarsophalangeal joint of the great toe. It is usually due to metatarsus primus varus which is medial deviation or adduction of the first metatarsal with an increased first - second metatarsal angle.
Halo sign in mammography refers to a radiolucent rim (halo) around a lesion and is generally but not always indicative of a benign breast lesion. Exceptions include intracystic carcinoma, papillary carcinoma, and carcinoma arising within a fibroadenoma.
halo sign (chest)
halo sign (u...
The halo sign (HS) in chest imaging is a feature seen on lung window settings (typically HRCT), ground glass opacity surrounding a pulmonary nodule or mass and represents haemorrhage. It is typically seen in angioinvasive aspergillosis.
Histopathologically, it represents a focus of p...
The hamate is one of the carpal bones, forms part of the distal carpal row and has a characteristic hook on its volar surface.
The hamate has a wedge-shaped body. It bears an uncinate (unciform) hamulus (hook of hamate) which projects in a volar fashion from the dista...
Hamatolunate impingement is an uncommon cause of ulnar-sided wrist pain. The condition occurs most commonly in wrists where there is type II lunate morphology (existence of a medial facet on the distal lunate for articulation with the hamate). Repeated impaction of the opposing articular surface...
Hamburg classification system of vascular malformations is one of the more commonly used systems to describe the wide range of vascular malformations, largely replacing the many various eponymous syndromes traditionally used. It accounts for the underlying anatomical, histological, and pathophys...
Hamman syndrome, also known as Macklin syndrome, refers to spontaneous pneumomediastinum along with subcutaneous emphysema.
It is a rare entity most often encountered in young adults. It is a known entity peri- and postpartum 3.
The condition is most common...
A hammertoe deformity is a flexion deformity of the foot where there is an abnormal flexion posture of the proximal interphalangeal (PIP) joint of one or more of the lesser toes. The PIP joint flexion deformity may be fixed or supple. With a severe hammertoe deformity, there is a compensatory hy...
Hampton hump refers to a dome-shaped, pleural-based opacification in the lung most commonly due to pulmonary embolism and lung infarction (it can also result from other causes of pulmonary infarction (e.g. vascular occlusion due to angioinvasive aspergillosis). While a pulmonary artery embolism ...
The Hampton line is a thin millimetric radiolucent line seen at the neck of a gastric ulcer in barium studies (profile view), indicating its benign nature. It is caused by a thin line of mucosa overhanging the ulcer's crater.
The hamstrings are the muscles of the posterior compartment of the thigh and include the:
lateral: biceps femoris
medial: semimembranosus and semitendinosus
Apart from the short head of biceps femoris, the muscles share two common features:
span both the hip and knee joints and therefore pro...
Hereditary angiopathy with nephropathy, aneurysms, and muscle cramps (HANAC) syndrome is an autosomal dominant monogenic COL4A1-related disorder.
The exact prevalence is unknown.
The cardinal features of HANAC syndrome are helpfully described in the name of...
The Nørgaard projection is also known as the ball-catcher view or posterior oblique view of both hands. It is an additional projection of the routine hand series. The ball-catcher view is often done to investigate signs of rheumatoid arthritis.
patient may be seated alongside...
The bilateral PA view often compliments the ball-catcher view. It is often done to investigate signs of rheumatoid arthritis and osteoarthritis.
patient may be seated alongside or facing the table
both hands are pronated with their palmer surfaces placed on the detector
Hand-foot-and-mouth disease is a viral illness that manifests as vesicular eruption on the hands and feet as well as painful ulcers of the oral mucosa. Symptoms usually resolve spontaneously in 7-10 days.
In most cases, there is a prodrome of fever, vomiting, diarrhoea, anorexia, and malaise.
All the intrinsic muscles of the hand are innervated by the ulnar nerve, except four muscles which are supplied by the median nerve and are easily recalled with the mnemonic:
FOAL or LOAF
F: flexor pollicis brevis
O: opponens pollicis
A: abductor pollicis brevis
L: lateral two lum...
The lateral hand view is an orthogonal view taken along with the PA view of the hand. Often an additional projection, the lateral view is used primarily to assess for foreign bodies and/or displacement of fractures/dislocations.
patient is seated alongside the table
hand is e...
The hand oblique view is part of a two view series metacarpals, phalanges, carpal bones and distal radial ulnar joint.
patient is seated alongside the table
the affected arm if possible is flexed at 90° so the arm and hand can rest on the table
the hand is rotated externall...
The Hand PA view is part of a two view series metacarpals, phalanges, carpal bones and distal radial ulnar joint.
patient is seated alongside the table
the affected arm if possible is flexed at 90° so the arm and hand can rest on the table
the affected hand is placed, palm ...
Hand radiographs are commonplace in the Emergency Department or the trauma reporting list.
Review the wrist
A hand radiograph contains a PA and oblique view of the distal radius and ulna and the carpus.
check the wrist as you would for a wrist radiograph (an approach)
The hand is part of the upper limb below the forearm and wrist. In the supinated anatomical position, the palm is facing anteriorly. The bones of the hand are:
Hand-Schüller-Christian disease is a clinically intermediate form of a spectrum of histiocytic disorders, which ranges from acute fulminant to chronic indolent disease. It primarily affects children, less often young adults, and rarely older adults.
Hand-Schüller-Christian disease has been desc...
The hand series is comprised of a posteroanterior and oblique, projection although additional radiographs can be taken for specific indications.
The series primarily examines the metacarpals, hamate, phalanges along with the carpal bones that are consisting of the scaphoid, lunate, triquetrum, ...
A hand series (or hand x-ray) may be performed for a multitude of reasons. However, they are most commonly used in the assessment of trauma, by clinical teams within the Emergency Department or Orthopaedic service.
This is a summary article. For more information, you can read...
Hanging noose sign in obstretric imaging is a rarely described but classical finding of a true umbilical cord knot. It demonstrates a transverse section of the umbilical cord surrounded by a loop of umbilical cord and changes in the pressure of the knot can be demonstrated with the fetus movemen...
Hangman fracture, also known as traumatic spondylolisthesis of the axis, is a fracture which involves the pars interarticularis of C2 on both sides, and is a result of hyperextension and distraction.
Post-traumatic neck pain after a high-velocity hyperextension injury is ...
A hard metal pneumoconiosis is usually classified as a type of fibrotic pneumoconiosis where the precipitating agent consists of a hard metal (not a heavy metal) such as.
tungsten / tungsten carbide alloys
or a mixture
A more broader term used is hard metal lung disease (...