Patella baja (or patella infera) is an abnormally low lying patella, which is associated with restricted range of motion, crepitations, and retropatellar pain. If longstanding, extensor dysfunction may ensue with significant morbidity. It is seen in a variety of clinical scenarios including 1:
Patellar tendon rupture is one of the extensor mechanism of the knee injuries and occurs almost invariably at either the patellar or tibial insertion of the patellar tendon, when in the setting of trauma, and is often associated with a small avulsion fracture. Most commonly, it is at the superi...
Patellar tumours are extremely rare. They can be either benign or malignant primary bone tumours, or metastases.
Patellar tumours represent just 0.1% of all primary bone tumours 1.
Patients may present with anterior knee pain and/or a palpable mass 1,3.
Pathological fractures are fractures that occur in abnormal bone. Although the term can be used in the setting of a generalised metabolic bone disease, it is usually reserved for fractures through a focal abnormality. The abnormality may be malignant or non-malignant in nature.
Pattern of bone contusion in knee injuries can give clues for the mechanism and associated injuries.
Five classic bone contusion patterns have been described 1-4:
valgus stress to flexed and externally rotated knee
contusion pattern: posterolateral ...
Neonatal hypoxic ischaemic brain injuries can manifest in different patterns of involvement depending on the severity and timing of the insult. When considering the perinatal maturation process of the brain and the severity of an insult, it is possible to understand the various manifestations.
Pear-shaped (or tear-drop-shaped) bladder is one whose normal round or ovoid shape has been extrinsically compressed to resemble a pear. The pear may be inverted or upright, depending on how the excess pelvic tissue compresses the bladder.
Causes of a pear-shaped bladder i...
A pedunculated intratracheal mass has a variety of differential diagnoses:
benign tumour, e.g. hamartoma, chrondroma, lipoma
metastasis to tracheal mucosa, e.g. renal cell carcinoma, melanoma
polyp, e.g. inflammatory, antrochoanal
Pelvic digit, also known as a pelvic rib, pelvic finger or 11th finger, is a rare congenital abnormality where there is development of bony tissue in the soft tissue pelvis and less commonly in the abdomen. They can be associated with one or more pseudoarticulation. They are usually unilateral, ...
Pelvic masses in females carry a broad differential diagnosis:
benign adnexal cyst: 34%
pelvic malignancy: 14%
pelvic inflammatory disease: 8%
Extra-gynaecological masses, e.g. colorectal carcino...
It is important to have a systematic way of approaching a case with pelvic pain in the exam.
Most examinations are performed using ultrasound. Always say that you would further assess the uterus with 3D ultrasound. You may also say that in my department we would perform a sonohysterogram. Only...
Pencil-in-cup deformity is the description given to one of the appearances on plain radiograph in psoriatic arthritis.
The appearance results from periarticular erosions and bone resorption giving the appearance of a pencil in a cup.
Although classically described with psoriatic arthritis, thi...
Penetrating traumatic neck injury can be a potentially devastating injury due to the high density of crucial anatomical structures within the neck.
Young males are highly represented in patients with a traumatic neck injury. In one study, 11:1 ratio of males to females were ident...
Periampullary tumours are those that arise within 2 cm of the ampulla of Vater in the duodenum.
Tumours that fall under this group include four main types of tumours 1,4 that will be approached in their specific articles:
pancreatic head/uncinate process tumours: includes pancreatic ductal ade...
Common causes of periarticular soft tissue calcification include:
post surgical dystrophic calcification or heterotopic bone formation
calcific tendinitis or bursitis
calcific periarthritis (fingers and toes)
Pericardial calcification usually occurs in patients with a history of pericarditis.
previous trauma or prior pericarditis
later sequelae of rheumatic heart disease
malignant pericardial involvement (e.g. mediastinal teratoma)
On chest radiography, location of...
Pericarditis is defined as inflammation of the pericardium. It is normally found in association with cardiac, thoracic or wider systemic pathology and it is unusual to manifest on its own.
In general, infection is the most common cause of pericarditis. Infection accounts for two-thir...
Perifissural lung nodules (PFNs) are a type of intrapulmonary nodules. They commonly represent intrapulmonary lymph nodes 1. There is some overlap with the term perilymphatic pulmonary nodules since the latter can be perifissural.
PFNs are typically seen as we...
Perigestational haemorrhage refers to haemorrhage that occurs around the fetus during the gestational period. The spectrum of haemorrhage includes:
chorionic haemorrhage: caused by the separation of the chorion from the endometrium
subchorionic haemorrhage: most common type, occurs between th...
Perilymphatic lung nodules follow perilymphatic channels and on imaging are typically subpleural, occur along fissures, interlobular septae and adjacent to the bronchovascular bundles.
Lung nodules in a perilymphatic distribution can be seen in association with a number ...
Perinephric fluid collections are commonly seen after renal transplantation. The appearance of a perinephric fluid collection is often nonspecific, and generating a differential often relies on when the transplant occurred.
Early post-transplant period
Periosteal reaction in the paediatric population, also known as periostitis in children, is relatively common occurrence and can result from many causes.
The differential diagnosis for multiple bone periostitis include but not limited to the following:
Periosteal reaction, also known as periostitis or periosteitis, is a non specific radiographic finding that occurs with periosteal irritation. Periosteal reactions may be broadly characterised as benign or aggressive, or more specifically broken down by pattern.
Benign versus ag...
Periportal hyperechogenicity can result from many causes including:
schistosomiasis of the portal region
recurrent pyogenic cholangitis (oriental)
inflammatory bowel disease: has been described to give "echo-rich" periportal cuffing 2
It may also be observed in ...
Periportal hypoechogenicity can result from many causes:
orthotopic liver transplant rejection
malignant lymphatic obstruction
Peritoneal calcification is seen in a limited number of conditions that result in calcification of peritoneal structures. Therefore, the differential diagnosis is small:
psammoma bodies in malignancy (most frequently cystadenocarcinoma of the ovary): fine sand-like calcification
Peroneal tubercle hypertrophy refers to the presence of an unusually large peroneal tubercle.
Two bony projections or protuberances may be seen from the lateral wall of the calcaneus – the peroneal tubercle and the retrotrochlear eminence.
The peroneal tubercle is presen...
It is important to have a systematic way of approaching a case with per vaginal bleeding in the exam.
intrauterine fetal demise
Pes planus (also called flatfoot) is a deformity of the foot where the longitudinal arch of the foot is abnormally flattened.
It results from loss of the medial longitudinal arch and can be either rigid or flexible. These deformities are usually flexible, which means that on non-weig...
PET-CT is a combination of cross-sectional anatomic information provided by CT and the metabolic information provided by positron emission tomography (PET).
PET is most commonly performed with 2-[F-18]fluoro-2-deoxy-D-glucose (FDG). Fluorine-18 (F-18) is an unstable radioisotope and has a half-...
There is a wide differential diagnosis of petrous apex lesions:
petrous apex cephalocoele 4
cholesterol granuloma: most common cystic appearing lesion 3
mucocoele of petrous apex 2
Phleboliths are literally "vein stones", and represent calcification within venous structures. They are particularly common in the pelvis where they may mimic ureteric calculi, and are also encountered frequently in venous malformations. There is an association with Maffucci syndrome.
Phocomelia is an extremely rare congenital skeletal disorder that characteristically affects the limbs. It can affect either the upper limbs or lower limbs or both. Phocomelia is also a descriptive term to describe the characteristic limb anomalies occurring with its associated conditions.
Photopsias are a visual phenomenon experienced by individuals with a variety of ocular or optic pathway pathology. In lay terms they represent flashing lights, and can be divided into unstructured or structured photopsias, the latter referring to geometric shapes 2.
Phrenic nerve palsy has many causes, and can be caused by lesions anywhere along the course of the phrenic nerve, as it travels from the neck, to pierce the diaphragm adjacent to the pericardium.
No single demographic is affected, as there are numerous causes of a phrenic nerve pa...
Phthisis bulbi, also known as end-stage eye, is an atrophic scarred and disorganised globe that may result from a variety of severe ocular insults.
The globe is reduced in size (usually <20 mm) with a thickened/folded posterior sclera. Dystrophic calcification is common, and osseous...
Picture archiving and communication system (PACS) is a modality of imaging technology which helps in image transmission from the site of image acquisition to multiple physically-disparate locations. This technology not only is economical (film-less department), but also convenient to access mult...
Pineal parenchymal tumours comprise a group of related tumours ranging from the relatively benign to the highly malignant. This group comprises of:
14-30% of pineal parenchymal tumours 2
mature well-differentiated tumour
WHO grade I
pineal parenchymal tumour with intermediate di...
A simple and popular mnemonic to remember the common suprasellar/parasellar/intrasellar masses is SATCHMO. The more comprehensive list includes:
pituitary adenoma (commonest in the adult population)
The five most common masses in the pituitary region are:
suprasellar pilocytic astrocytoma
Craniopharyngioma and suprasellar pilocytic astrocytoma are common in children, and pituitary macroadenoma, meningioma, aneurysm are mostl...
Pituitary region mass with an intrinsic high T1 signal, also referred as suprasellar hotspots, are relatively frequently encountered, and the presence of high T1 signal narrows the differential somewhat.
pituitary macroadenoma with haemorrhage/necrosis
Pituitary tumours, in other words, tumours which arise from the pituitary gland itself, include:
spindle cell oncocytoma (rare)
Often the term is used more broadly to refe...
Placentomegaly is a term applied to an abnormally enlarged placenta.
It can be associated with number of maternal and fetal disorders which include:
chronic intrauterine infections
Pleural adhesions usually refers to the formation of fibrotic bands that span the pleural space, between the parietal and visceral layers of the pleura.
They may be local or diffuse. The presence of a pleural adhesion is one of the causes for a pneumothorax not to resolve.
Pleural calcification can be the result of a wide range of pathology and can be mimicked by a number of conditions/artifacts.
calcified pleural plaques from asbestos exposure: typically has sparing of costophrenic angles
infection involving the pleura: e.g pyot...
Pleural effusion tends to be used as a catch-all term denoting a collection of fluid within the pleural space. This can be further divided into exudates and transudates depending on the biochemical analysis of aspirated pleural fluid (see below). Essentially it represents any pathological proces...
Pleural involvement with lymphoma can occur in two situations:
primary pleural lymphoma
primary effusion lymphoma
secondary involvement of the pleura with lymphoma
Pleural thickening is a descriptive term given to describe any form of thickening involving either the parietal or visceral pleura.
It can occur with both benign and malignant pleural disease. According to aetiology it may be classified as:
benign pleural thickening
following recurrent infla...
There are several tumours that can involve the pleura which can range from being benign to malignant. The list includes:
primary pleural tumours
malignant pleural mesothelioma
pleural fibroma: solitary fibrous tumour of the pleura
primary pleural ly...
Pneumatoceles are intrapulmonary air-filled cystic spaces that can have a variety of sizes and appearances. They may contain air-fluid levels and are usually the result of ventilator-induced lung injury in neonates or post-infectious. They should not be mistaken for a cavitating lung mass.
Pneumatosis coli is a descriptive sign presenting radiographically as intramural gas limited to the colonic wall.
There are different terminologies in the medical literature, such as pneumatosis intestinalis, pneumatosis coli, and pneumatosis cystoides intestinalis. Pneumatosis in...
Pneumoconioses are a broad group of lung diseases that result from inhalation of dust particles. It is therefore considered part of the spectrum of inhalational lung disease.
The offending agents are mainly mineral dust. They can be broadly classified as 2-3:
Pneumonectomy is the complete surgical removal of the lung. It is most commonly performed for a primary lung malignancy. The lung is removed in its entirety providing the patient has adequate pulmonary reserve from the contralateral lung.
Recognised post-pneumonectomy complications include:
Pneumonia is a general term in widespread use, defined as infection within the lung. It is due to material, usually purulent, filling the alveoli.
Pneumonia is in contrast to pneumonitis, which is inflammation of the pulmonary interstitium. Of note, some of the interstitial lung di...
Pneumoparotid refers to air in the parotid gland and can cause unilateral/bilateral parotid swelling. In severe cases it can be associated with subcutaneous emphysema.
Any profession or recreation that increases oral positive pressure can cause air to reflux up the parotid ducts int...
Pneumoretroperitoneum is by definition presence of gas within the retroperitoneal space.
Pneumoretroperitoneum is always abnormal and has a relatively small differential:
perforated retroperitoneal hollow viscus
peptic ulcer disease
blunt or penetrating abdominal trauma
A pneumothorax does not display classical signs when a patient is positioned supine for a chest radiograph. Instead, the pneumothorax may be demonstrated by looking for the following signs:
relative lucency of the involved hemithorax
deep, sometimes tongue-like, costophrenic sulcus: deep sulcu...
Polyarticular arthropathy can arise from a number of causes. The list includes
Polyhydramnios refers to a situation where the amniotic fluid volume is more than expected for gestational age.
It is generally defined as:
amniotic fluid index (AFI) >25 cm
largest fluid pocket depth (maximal vertical pocket (MVP)) greater than 8 cm 6: although some centres particularly in A...
Polymyalgia rheumatica (PMR) is a common inflammatory condition typically affecting elderly people. It is a multisystem disorder but usually affects the musculoskeletal system.
It can manifest in various ways, which are best discussed in the separate articles below:
polymyalgia rheumatica: mus...
Common causes of polyostotic bone lesions in adults include:
arthritic or synovial-based lesions
nonossifying fibromas (fibroxanthomas)
polyostotic fibrous dysplasia (McCune-Albright syndrome)
Porcelain left atrium, also known as coconut left atrium, is a term used when a large part of or the entire left atrial wall becomes calcified. It can occur as a rare consequence of endocarditis (with underlying rheumatic heart disease). It has also been described in the setting of end-stage ren...
Portal venous gas is the accumulation of gas in the portal vein and its branches. It needs to be distinguished from pneumobilia, although this is usually not too problematic, when associated findings are taken into account along with the pattern of gas (i.e. peripheral in portal venous gas, cent...
Posterior fossa astrocytomas, those arising either from the cerebellum or from the brainstem are most frequently seen in children. Approximately 60% of all paediatric astrocytomas are found in the posterior fossa (20% brainstem, 40% cerebellum).
Many types of astrocytoma are found in the poster...
Posterior inferior cerebellar artery (PICA) occlusion may cause infarction of any of the vascular territory of the PICA, namely the posterior inferior cerebellum, inferior cerebellar vermis and lateral medulla.
Typically considered the most common territory involved in cerebellar ...
The differential diagnosis for a posterior mediastinal mass includes:
neurogenic tumours - most common
nerve sheath tumours
malignant peripheral nerve sheath tumour
parasymphathetic ganglion tumours
Posterior shoulder dislocations are far less common than anterior shoulder dislocations and can be difficult to identify if only AP projections are obtained. I high index of suspicion is helpful.
Posterior shoulder dislocations account for only 2-4% of all shoulder dislocations (t...
Post-obstructive pulmonary oedema is a type of non-cardiogenic pulmonary oedema and is an uncommon but well-described complication of upper airway obstruction.
It essentially occurs in three clinical settings 6:
acute airway obstruction
chronic upper airway obstruction
Post surgical breast scar is a benign complication that usually occurs following surgical intervention to breast tissue. It can however be a strong and potentially very confusing mimicker of breast malignancy.
Review of the patient's past history and previous mammography...
A Pott shunt is a form of palliative surgery performed in patients with tetralogy of Fallot prior to the ability to repair the defect. It consists of a shunt formed between the descending thoracic aorta and the left pulmonary artery.
This does not relieve the right ventricular outflow obstructi...
Powers ratio is a measurement of the relationship of the foramen magnum to the atlas, used in the diagnosis of atlanto-occipital dissociation injuries.
The ratio, AB/CD, is measured as the ratio of the distance in the median (midsagittal) plane between the:
basion (A) and the posterior spinola...
Pre-axial polydactyly refers to polydactyly where the additional digit is towards the first digit of the hand (radial side) or foot (medially).
Pre-axial polydactyly is less common than post-axial polydactyly, with an estimated incidence of 1 in 7000.
Pregnancy associated breast cancer (PABC) is usually defined as a breast breast cancer diagnosed during pregnancy or one year following delivery. PABC occurs in one out of every 1500-10,000 pregnancies 5-6 and represents up to 3% of all breast malignancies. The incidence may be increasing due to...
Pregnancy of uncertain viability (PUV) is a term given to an intrauterine pregnancy in a situation where there are not enough criteria (usually on ultrasound grounds) to confidently categorise an intrauterine pregnancy as either viable or a failed pregnancy.
Pre-invasive lesions of the lung are a category of lesions which have not yet progressed to malignancy but have the potential to do so.
This category includes:
squamous dysplasia (SD) of lungs: squamous cell carcinoma in situ (CIS) of lung
atypical adenomatous hyperplasia (AAH)
Premature closure of a growth plate subsequently results in a shortened bone, which can occur in a number of situations.
juvenile chronic arthritis
juvenile rheumatoid arthritis
Primary benign cardiac tumours are much less common than secondary metastatic deposits. However they are more likely when a cardiac mass is seen outside of the setting of terminal metastatic disease. Tumours include 1-2:
most common in adults
accounts for ~50% of all primary be...
The most common tumour of the spine is metastatic deposits. A number of both benign and malignant tumours may arise primarily from the spine.
giant cell tumour (GCT)
aneurysmal bone cyst (ABC)
eosinophilic granuloma (EG)
Primary immunodeficiency states are heterogenous group of disorders that occur when there is an impairment of humoral or cell-mediated immunity in the absence of any recognised precipitating cause such as drug therapy or infective agent such as human immunodeficiency virus (HIV).
There are a number of primary malignancies of the nasopharynx:
nasopharyngeal carcinoma (squamous cell carcinoma): 70%
lymphoma (sinonasal lymphoma): 20%
adenoid cystic carcinoma
Primary malignant cardiac tumours are rare, and account for only ~25% of primary cardiac tumours, and only a small proportion of all malignant tumours which involve the heart: direct extension of adjacent tumours or metastatic deposits are far more common. Histologcal types include 1:
Although primary tumours of the thymus are rare, they are the most common causes of a neoplasm of the anterosuperior mediastinum 1.
one-third are benign
two-thirds are malignant
invasive thymoma (most)
thymic carcinoma (rare)
Primary peritoneal neoplasms comprise of an uncommon group of heterogenous entities.
The list includes:
primary (malignant) peritoneal mesothelioma
primary perioneal multicystic mesothelioma
primary peritoneal well differentiated papillary mesothelioma
Primary pneumatosis intestinalis (PPI) is a benign idiopathic condition in which multiple gas-filled cystic lesions are seen in the gastrointestinal tract wall. The changes are usually seen initially on radiography or CT with CT being the more sensitive test.
Primary pneumatosis i...
Primary pulmonary tuberculosis is seen in patients not previously exposed to Mycobacterium tuberculosis.
It is most common in infants and children and has the highest prevalence in children under 5 years of age 1.
Primary pulmonary tuberculosis manifests as...
Programmable cerebrospinal shunts are a type of ventriculoperitoneal shunt that can be set to different CSF pressure settings. It is of particular value in normal pressure hydrocephalus and in paediatrics patients.
The 2010 AJNR article by Lollis et al. 1 provides radiographic features of the s...
Proptosis refers to forward protrusion of the globe with respect to the orbit. There are many causes of proptosis which can be divided according to location and it is worth remembering that it is not just orbital disease processes that cause proptosis.
Exophthalmos also describes f...
Prosopagnosia is the inability to recognise faces. There are varying degrees of impairment and only the recognition of familiar faces can be affected. There is usually preservation of other aspects of visual processing and intellectual functioning. With the most extreme impairment the sufferer c...
Transrectal ultrasound–guided biopsy is considered the standard approach for prostate biopsy and is most commonly performed on an outpatient with a positive screening for prostate cancer.
Nowadays, with the MRI capacity for depicting abnormal areas of the prostate, is possible to obtain target...
Prostate cystic disease encompasses a wide variety of pathologies that all result in cyst formation within the prostate.
Prostatic cysts are common, and ~5-8% men will develop one 4,7. However they are much more common in patients being investigated for infertility, with one study showing a 20%...
Prostate peripheral zone T2 hypointensity is a common finding in pelvic MRIs that needs to be differentiated. A prostate directed MRI is usually performed using a multi-parametric technique to differentiate prostate cancer from more benign changes. This includes T2 weighted images, dynamic contr...
Prostatic utricle cyst (PUC) is an area of focal dilatation that occurs within the prostatic utricle.
They are midline cystic masses in the male pelvis and can be very difficult or impossible to distinguish from a Mullerian duct cyst.
Utricle cysts are most often detected in the ...
Prostatomegaly is a term used to generally describe enlargement of the prostate gland from whatever cause. Usually the prostate is considered enlarged on imaging when it measures beyond 30 cc (30 grams) in size.
The term prostatomegaly is often used interchangeably with benign pro...