P-value is defined as the probability that the difference between the means of two studies is not just due to chance. The values range between zero to one.
By convention, p-value <0.05 is considered statistically significant.
The p-value is used in deciding if the null hypothesis made befor...
Pachydermoperiostosis (PDP) refers to rare osteo-arthro-dermopathic syndrome with familial and idiopathic forms. It is also known as primary hypertrophic osteoarthropathy because it is not due to a secondary cause such as lung disease.
PDP most commonly affects black people and ad...
A number of paediatric cardiovascular procedures are encountered when reporting paediatric imaging. They include:
Blalock Taussig (BT) shunt
classic: end to side subclavian to ipsilateral pulmonary arterial anastomosis
modified: graft anastomsis
Sano shunt: right ventricle t...
The clavicle is a unique bone and as such it often displays unique pathology. The following is an attempt to summarise paediatric clavicle abnormalities.
Paediatric bone tumours and tumour-like lesions of the clavicle
majority of clavicular tumours are malignant
Ewing sarcoma (most common)
The paediatric curriculum is one of our curriculum articles and aims to be a collection of articles that represent the core paediatric knowledge.
Topics pertaining to paediatric radiology, including paediatric neuroradiology and fetal radiology, although there will be some cross cov...
The paediatric cystic renal diseases comprises a group of conditions that are all either autosomal recessive or non-hereditary:
autosomal recessive polycystic kidney disease (ARPKD):
hyperechoic and enlarged kidney
multicystic dysplastic kidney (MCDK):
absence of functional parenchyma, urete...
Paediatric elbow radiographs are commonly encountered in the emergency department and when approached in a standard fashion, not as difficult to interpret as most people think!
Check that the ossification centres are present and in the correct position. They app...
The paediatric kidneys follow a growth curve. The measurements below are of the longest maximal dimension. Measurements in parentheses are one standard deviation.
0 months 1: female: 4.15 cm (0.35); male: 4.22 cm (0.32)
2 months: 5.28 cm (0.66)
6 months: 6.15 cm (0.67)
10 months: 6.23 cm (0...
Pulmonary lung lesions are a heterogenous group of lung lesions:
lung agenesis-hypoplasia complex
hypogenetic lung syndrome (Scimitar syndrome)
Paediatric cystic lung lesions:
congenital lobar emphysema
congenital cystic adenomatoid...
Paediatric mediastinal masses are the most common chest masses in children, with the anterior mediastinum being the most common site 1.
As in adults, mediastinal masses are classified depending on anatomical sites:
anterior mediastinal masses
middle mediastinal masses
posterior mediastinal m...
This classification system based on the embryology and anatomy of the nasal cavity, nasofrontal region, and nasolacrimal apparatus as well as anomalies associated with craniofacial syndromes.2
choanal atresia and stenosis
pyriform aperture stenosis
Tumours of the posterior fossa in children can be remembered using the mnemonic:
The mnemonic is not in order of prevalence; pilocytic astrocytomas are most common.
B: brainstem glioma
A: astrocytoma (pilocytic) (85%)
Paediatric renal tumours and masses are another group of diseases (just like cystic renal diseases in both the adult and child) that are bewildering in their number, nomenclature and overlapping findings.
Wilms tumour: common in older children 1-8 years old
Paediatric shoulder radiographs are usually performed after trauma in older children. However, seat-belt injuries during motor vehicle accidents can cause shoulder trauma at any age. Birth trauma may also be factor.
Check the cortex and review alignment:
if there i...
There is a wide range of primary malignancies that results in paediatric skeletal metastases 1:
leukaemia: although not truly metastases
clear cell sarcoma: Wilms’ variant
Ewing’s sarcoma: lung metastases much more common
Paediatric urinary tract infections are common and are a source of significant imaging in young children.
Paediatric urinary tract infections affect up to 2.8% of all children every year, with approximately 2% of boys and 8% or more of girls developing a urinary tract infection at...
The British National Institute for Health and Care Excellence (NICE) published in 2007 the “Urinary tract infection in under 16s: diagnosis and management” as a guideline for paediatric urinary tract infection (UTI) management, including imaging, prophylaxis and follow-up 1.
This article inden...
Page kidney refers to the phenomenon of hypertension that develops following long-standing compression of renal parenchyma by subcapsular renal collection, e.g. haematoma, seroma, urinoma.
Compression of the renal parenchyma results in compression of the renal vessels, which leads to...
Paget disease can refer to either:
Paget disease of bone
Paget disease of breast
History and etymology
Both conditions are named after Sir James Paget (1814-1899), British surgeon and physiologist.
Paget disease of the bone is a common, chronic bone disorder characterised by excessive abnormal bone remodelling. It frequently affects the pelvis, spine, skull and proximal long bones and has characteristic radiographic features.
It is relatively common and can affect up to 4% o...
Paget disease of the breast (which is also known as Paget disease of the nipple) has traditionally been described as a form of breast malignancy characterised by infiltration of the nipple epidermis by malignant cells. Although most case have underlying focus or foci of in situ or invasive carci...
Paget-Schrötter syndrome, alternatively spelled Paget-Schroetter syndrome and also known as effort thrombosis, refers to primary thrombosis of the axillary and/or subclavian vein. It can be thought of as a venous equivalent of thoracic outlet syndrome.
It is associated with forced...
A paintbrush appearance is termed to describe the streaky appearances of dilated contrast filled tubules within the renal medulla on IVP or CT-IVU. This appearance is characteristic for medullary sponge kidneys.
bouquet of flowers appearance
Pair production (PP), like the photoelectric effect, results in the complete attenuation of the incident photon. Pair production can only occur if the incident photon energy is at least 1.022 MeV. As the photon interacts with the strong electric field around the nucleus it undergoes a change of ...
The paired t-test is the appropriate method when the researcher takes an experimental group, measures the baseline, subjects the members to an intervention, and then measures the results.
Testing in a before-and-after manner like this ("matched data" or "repeated measures") ...
Pallister-Killian syndrome (PKS) is an extremly rare chromosomal anomaly.
It may be more prevalent in woman of advanced age 4.
It is a polymalformative complex with tetrasomy of isochromosome 12p although many cases are mosaic.
The majority of cases are th...
Pallister-Hall syndrome is characterised by:
renal anomalies, e.g horseshoe kidney
The palmaris brevis, a small intrinsic muscle of the hand, is a quadrangular-shaped subcutaneous muscle that overlies the hypothenar muscles, ulnar artery and superficial branch of the ulnar nerve at the medial side of the palm.
palmar aponeurosis and flexor retinaculum
Palmaris longus (PL) is a superifical, weak flexor of the wrist located in the anterior compartment of the forearm.
Palmaris longus is often absent, more commonly unilaterally absent than bilaterally. There is ethnic variation in prevalence of absence:
absence in ~3% of Asians
absence in ~5% ...
Palmer classification for triangular fibrocartilage complex (TFCC) abnormalities is based on the cause, location and degree of injury 1:
Class 1 - traumatic injury
a: central perforation
b: ulnar avulsion with or without distal ulnar fracture
may involve the proximal or distal lamina (foveal...
Palmini classification of focal cortical dysplasia published in 2004 was one of the leading classification systems used for focal cortical dysplasia, recently replaced by a newer classification; Blumcke classification of focal cortical dysplasia.
Unfortunately, as is the case with many classif...
The term panbronchiolitis refers to a bronchiolitis affecting throughout the lungs. Most radiological publications describe this as diffuse panbronchiolitis.
Pancake brain, is the classical sign of alobar holoprosencephaly. It is due to fusion of the cerebral hemispheres leaving a single ventricle in its center. It is the most severe form of holoprosencephaly. It is associated with multiple facial abnormalities.
Pancake kidney (also known as discoid kidney, disc kidney, lump kidney, fused pelvic kidney or cake kidney) is a rare renal fusion anomaly of the kidneys of the crossed fused variety.
Pancake kidney may be an incidental finding. However, they can present clinically becaus...
Pancoast syndrome results from involvement of brachial plexus and sympathetic chain by a Pancoast tumour, or less commonly from other tumours involving the superior pulmonary sulcus. The syndrome consists of:
C8-T2 radicular pain
The classical syndrome is uncomm...
Pancoast tumour, otherwise known as superior sulcus tumour, refers to a relatively uncommon situation where a primary bronchogenic carcinoma arises in the lung apex and invades the surrounding soft tissues.
Definitions vary from author to author, with some only referring to Pancoas...
The pancreas is a retroperitoneal organ that has both endocrine and exocrine functions: it is involved in the production of hormones (insulin, glucagon and somatostatin), and also involved in digestion by its production and secretion of pancreatic juice.
The pancreas can be divid...
Pancreas divisum represents a variation in pancreatic ductal anatomy that can be associated with abdominal pain and idiopathic pancreatitis. It is characterised, in the majority of cases, by the dorsal pancreatic duct (main pancreatic and Santorini ducts) directly entering the minor papilla wit...
A pancreas transplant is a procedure performed in some medical centers in which a donor pancreas is transplanted to a recipient. The donor pancreas is typically cadaveric, but may rarely be a segment from a living donor 1. The transplant is meant to establish normoglycemia in patients with dia...
Pancreatic atrophy is non-specific is common in elderly patients, although in younger patients it can be a hallmark of pathology. Most commonly it is associated with aging, obesity and end-stage chronic pancreatitis.
It occurs principally with fatty replacement of the pancreas (pancreatic lipo...
Pancreatic calcifications can arise form many aetiologies.
Punctate intraductal calcifications
acute alcoholic pancreatitis (20-40%)
intraductal, numerous, small, irregular
preponderant cause of diffuse pancreatic intraductal calcification
idiopathic: no underlying ca...
The diameter of the (main) pancreatic duct is a commonly assessed parameter in imaging.
The duct diameter is greatest at the head and neck region and is slightly narrower towards the body and tail. Its normal reported value ranges between 1-3.5 mm 5, 8:
head: 3.5 mm
body: 2.5 m...
Pancreatic ductal adenocarcinoma makes up the vast majority (~90%) of all pancreatic neoplasms and remains a disease with very poor prognosis and high morbidity.
On imaging, it usually presents as a hypodense mass on CT that is poorly marginated, which may encase vessels and the common biliary ...
Both endocrine and exocrine tumours of the pancreas are now staged by a single pancreatic staging system.
Staging of pancreatic ductal adenocarcinoma is with the TNM system, and as a majority of tumours are not-resectable, this is mostly achieved with imaging (typically CT scan) although laparo...
The pancreatic ductal embryology is moderately complicated, leading to a number of anatomical variants of the pancreatic ducts, many of which are clinically significant.
The normal arrangement is for the entire pancreas to be drained via a single duct, to the ampulla of Vater through the sphinc...
Pancreatic intraductal tubulopapillary neoplasms (ITPNs) are rare variants of intraductal papillary neoplasms. Unlike an IPMN, an ITPN does not produce mucin.
Incidence/prevalence is unclear. Small series show an even male:female distribution and an average age of presentation of ...
Pancreatic intraepithelial neoplasia (PanIN) is a precursor lesion to pancreatic ductal adenocarcinoma, but the frequency at which this transition occurs is unknown.
Increasing incidence with age 1. Risk factors:
pancreatic lipomatosis 3
More commonly locat...
Pancreatic lipomas are uncommon mesenchymal tumors of the pancreas.
Rarely symptomatic, they are more often detected incidentally on cross-sectional imaging for another purpose. If they do cause symptoms, it will typically be those related to regional mass effect from the...
Pancreatic lipomatosis refers to fatty replacement of pancreatic parenchyma. This finding is most often associated with obesity and aging.
It tends to be commonest pathological condition involving the pancreas. The condition may occassionally simulate a mass like lesion particularly when fatty...
Pancreatic lymphangiomas are benign lesions that are often found incidentally during cross-sectional imaging for another reason.
More common in adults (in contrast to lymphangiomas in the head and neck, which are more common in children). Account for approximately 1% of a...
Pancreatic lymphoma is most commonly a B-cell sub-type of non-Hodgkin lymphoma and is classified as either primary or secondary:
primary pancreatic lymphoma is a rare extranodal manifestation of any histopathologic subtype of B-cell non-Hodgkin's lymphoma, representing < 2% of extranodal lym...
Pancreatic mesenchymal neoplasms (or pancreatic nonepithelial neoplasms) are a group of rare pancreatic neoplasms that arise from the structural elements of the pancreas (nerves, fat, lymph), rather than from the exocrine or endocrine cells of the pancreas. Neoplasms from exocrine and endocrine ...
Pancreatic metastases are uncommon and are only found in a minority (3-12%) of patients with widespread metastatic disease at autopsy . They account for only 2-5% of all pancreatic malignancies.
Although essentially any primary may eventually deposit in the panaceas the most common primaries en...
There are numerous primary pancreatic neoplasms, in part due to the mixed endocrine and exocrine components.
Classification based on function
exocrine: ~99% of all primary pancreatic neoplasms
pancreatic ductal adenocarcinoma ~90-95%
intraductal papillary muc...
Pancreatic neurofibromas are rare nonepithelial neoplasms of the pancreas. They are similar to neurofibromas found elsewhere in the body, and are associated with neurofibromatosis type I.
If they do cause symptoms, it will typically be those related to regional mass effe...
Pancreatic perivascular epithelioid cell tumours (or "Pancreatic PEComas") are a subtype of the larger family of PEComas. Pancreatic PEComas are very rare with <20 cases described.
More common in adults (in contrast to lymphangiomas in the head and neck, whic...
Pancreatic pseudocysts are common sequelae of acute pancreatitis or chronic pancreatitis, and the most common cystic lesion of the pancreas. They are important both in terms of management and differentiation from other cystic processes or masses in this region.
The following are th...
The pancreas is uncommonly injured in blunt trauma; however, pancreatic trauma has a high morbidity and mortality.
The pancreas is injured in ~7.5% (range 2-13%) of blunt trauma cases 1,3. Motor vehicle accidents account for the vast majority of cases.
A number of pancreatic injury grading systems have been proposed.
American Association for Surgery in Trauma (AAST)
grade 1: haematoma with minor contusion/laceration but without duct injury
grade 2: major contusion/laceration but without duct injury
grade 3: distal lacerati...
Pancreatic ultrasound can be used to assess for pancreatic malignancy, pancreatitis and its complications, as well as for other pancreatic pathology.
Proper preparation of the patient is necessary, with a minimum time of last meal of 4-6 hours prior to examination. If the patient i...
Pancreatitis refers to inflammation involving the pancreas.
It has various forms which can be classified in many many ways according to time of onset, aetiological agent or associated pathology.
interstitial oedematous pancreatitis
Pancreatoblastomas are rare paediatric tumours of the pancreas. However, they are the most common pancreatic neoplasm of childhood and are often associated with a raised alpha-fetoprotein.
There is slight male predilection. Usually occurs in the first decade of life with a mean ag...
The humble panda has a few signs to its name:
panda sign of the midbrain
panda sign of sarcoidosis
animal and animal produce inspired signs
The panda sign of sarcoidosis is a gallium-67 citrate scan finding. It is due to bilateral involvement of parotid and lacrimal glands in sarcoidosis, superimposed on the normal uptake in the nasopharyngeal mucosa.
The presence of perihilar adenopathy adds the lambda distribution of increased up...
The panda sign in neuroimaging refers to the appearance of the midbrain, when the red nucleus and substantia nigra are surrounded by high T2 signal.
It is classically seen in Wilson disease, although whenever the white matter is diffusely abnormal in the region a similar appearance will be perc...
Panlobular emphysema is a morphological descriptive type of emphysema that is depicted by permanent destruction of the entire acinus distal to the respiratory bronchioles with no "obvious" associated fibrosis.
Panacinar emphysema is characterised by permanent destruction of...
Panner disease is an osteochondrosis of the capitellum. It should be distinguished from osteochondritis dissecans of the elbow which also affects the capitellum.
Panner disease is typically seen in children (5-10 years of age), although it is also seen in throwers due to repeated...
A pantaloon hernia (dual hernia or Romberg's hernia or saddle bag hernia) is defined as ipsilateral, concurrent direct and indirect inguinal hernias. Hernial sacs are present on both sides of the inferior epigastric vessels, and separated by the posterior wall of the inguinal canal brought down ...
Pantopaque is an oily contrast medium that used to be used for myelography. Its generic name is iodophenylundecylic acid and it was first used in 1944.
A major drawback is the lack of resorption. Complete removal through aspiration is usually impossible after a procedure and the remaining drop...
Panzerherz (or armoured heart) is a term used to describe the appearance of the heart in calcified constrictive pericarditis.
The pericardium becomes circumferentially thickened with calcification, limiting the ability of the heart to contract. The rim of dense calcification describes how the h...
The Papez circuit is a fundamental component of the limbic system. It is a closed neural circuitry that starts and ends in the hippocampus. It is also known as the medial limbic circuit.
The Papez circuit involves different structures of the brain including 2:
hippocampus and a...
Papillary carcinoma of the breast is a rare ductal breast malignancy.
They are thought to account for 1-2% of breast carcinomas 2. They typically present in post menopausal patients with the mean age at being ~63-67 years.
A papillary carcinoma may manifest...
Papillary cystadenomas of the epididymis are the second most common benign tumours of the epididymis after adenomatoid tumours. They are more common in young men. Approximately 30% of the patients have von Hippel Lindau disease and approximately 10% to 40% of patients with von Hippel-Lindau dise...
Papillary fibroelastomas are rare benign primary cardiac tumours. However, of the primary cardiac tumours, they are one of the commonest to occur in relation to the cardiac valves (may account for 75% of valvular tumours 10).
Its estimated prevalence ranges between <0.01 to 0....
Papillary glioneuronal tumours are a newly recognised entity on the 2007 WHO classification of CNS tumours. It is a rare well circumscribed complex solid cystic supratentorial lesion with indolent clinical course.
Papillary glioneural tumours are a WHO grade I with low proliferation ...
Papillary lesions of the breast comprise of a wide group and can range from being benign to malignant.
They develop as tufts of epithelium with a ﬁbrovascular core that arborize into branching papillae and protrude into the duct lumen.
papilloma of breast / intraductal papil...
Papillary meningiomas (PM) are a rare subtype of malignant (WHO grade III) meningiomas that tends to occur in young patients and are characterised by an aggressive growth pattern illustrated by atypical imaging features such as brain and bone invasion. These tumours have a strong tendency of rec...
Papillary renal cell carcinoma (pRCC) is one of the subtypes of renal cell carcinoma.
This sub type may may account 13-20% of all renal cell cancer. There is slightly increased male predilection.
As with other types of of renal cell cancer, most are asympto...
A papillary serous carcinoma of the cervix (PSCC) is an uncommon histological type of cervical cancer. It is considered a sub type of adenocarcinoma of the cervix.
Accodring to some studies, there was a bimodal age distribution, with one peak occurring before the age of 40 years ...
Papillary serous carcinoma (PSC) of the endometrium is an uncommon histological subtype of endometrial cancer. It is considered type II endometrial adenocarcinoma and has a clinically aggressive form with early extension of the tumour via Fallopian tubes into the peritonium and peritoneal seedin...
Papillary squamous cell carcinoma (PSCC) of the cervix is a distinct subtype of squamous cell carcinoma of the cervix.
These tumours are characterised by a papillary architecture containing fibrovascular cores and moderate to severe dysplasia without any of frank keratinization and k...
Papillary thyroid carcinoma (PTC) is the most common malignancy of the thyroid gland, and frequently has nodal metastases at presentation.
Papillary thyroid cancer (as is the case with follicular thyroid cancer) typically occurs in the middle-aged, with a peak incidence in the 3rd...
Papillary tumour of the pineal region (PTPR) is a recently described entity only included in the most recent WHO classification 3, and are though perhaps to arise from specialised ependymocytes of the subcommissural organ located in the lining of the posterior commissure rather than from the pin...
Papilloedema is essentially an ophthalmoscopic diagnosis and refers to swelling of the optic disc. The MRI appearance relates to the dural anatomy of the optic nerve, which is continuous with the subarachnoid space, thereby allowing increased intracranial pressure (ICP) to be transmitted to the ...
Para-oesophageal hernias (POH), or rolling hernias, are an uncommon type of hiatal hernia representing ~10% of all hiatal hernias. The majority of the hiatal hernias being of the sliding type.
Can vary and can include:
gastro-oesophageal reflux disease (mai...
Para-tracheal air cysts are not uncommon in routine thoracic imaging. They characteristically occur on the right side. They occur in the region of the thoracic outlet.
They be present in approximately 3-4% of the population.They may be seen both children and adults. There may be ...
Paracaval lipoma (or juxtacaval fat collection) can be a frequent finding on CT and can seen in up to 0.5% of examinations 1. Some even consider this as a normal variation5. It occurs at the medial aspect of the intrahepatic portion of the inferior vena cava (IVC) above the caudate lobe and rep...
The paracentral lobule is located on the medial surface of the cerebral hemisphere, and includes parts of both the frontal and parietal lobes. It is the medial continuation of the precentral and postcentral gyri. It has motor and sensory functions related to the lower limb.
Parachordomas are rare neuroepithelial tumors with glial differentiation that are histologically similar to chordomas but do not occur in the axial skeleton.
They are generally slow growing and non-disseminating, and sometimes have late local recurrence after resection.
A parachute device improves the cardiac output by partitioning damaged heart muscle in the apical region from normal muscle, allowing improvement of cardiac output and functioning of the left ventricle in patients with ischaemic heart failure secondary to infarction.
Implantation is accomplishe...
A parachute mitral valve is valvular congenital abnormality usually identified in infants or young children though is can present later in adulthood.
Pathohysiology and natural history
It occurs when all the chordae tendineae are attached to a single papillary muscle origin. Unlike the normal ...
Paracicatricial emphysema is a morphological sub type of pulmonary emphysema.
In this form, emphysematous spaces are seen adjanent to areas of scarring with latter usually caused by silicosis, granulomatous infection, tuberculosis, pneumonia or pulmonary infarction.
Paradoxical brain herniation, also known as sinking skin flap syndrome (SSFS), is a rare and potentially fatal entity complicating decompressive craniectomy.
Atmospheric pressure exceeding intracranial pressure at the craniectomy results in displacement of the brain across various i...