Nipple shadows refer to the silhouettes of the nipples on frontal chest radiographs, which may mimic solitary pulmonary nodules (SPNs).
Nipple shadows are apparent on ~7.5% (range 3.5-11%) of frontal chest x-rays 1.
It has been proposed by Miller et al. that solitary p...
Nodular filling defects due to mucosal lesions in the duodenum are due to a number of processes. For a differential list which includes non-mucosal lesions see duodenal filling defects.
The differential diagnosis for mucosal lesions includes:
heterotopic gastric mucosa
Nodular pleural thickening is a form of pleural thickening.
Most common causes of nodular pleural thickening are malignant and include:
metastatic pleural disease, particularly from adenocarcinomas, e.g.
Non-calcified hyperdense pulmonary nodules are predominantly the result of inhalational exposure to substances, although embolization of material may cause dense nodular opacification within the lung.
inhalation disease, e.g. pneumoconioses
pulmonary baritosis (barium dust)
Non-neoplastic solid lesions of the pancreas are conditions which may mimic pancreatic neoplasms on imaging. They include:
intrapancreatic accessory spleen
peripancreatic lymph node
Non-seminomatous germ cell tumors (NSGCT) are one of the main groups of germ cell tumors (the other being seminoma). Although they are made up of distinct histological entities, in general, they have similar radiographic appearances. They can, however, be found widely in the body, with variable ...
Non-small-cell lung cancer represents a heterogeneous group of lung cancers that do not have "small cells" on histology. They are thus separated, as small cell carcinoma of the lung has distinctive management implications. The major histological types include:
adenocarcinoma of lung
Normal intracranial calcifications can be defined as all age-related physiologic and neurodegenerative calcifications that are unaccompanied by any evidence of disease and have no demonstrable pathological cause.
The most common sites include:
seen in 2/3 of the adult population ...
A list of normal radiological reference values is as follows:
adrenal gland: <1 cm thick, 4-6 cm length
aorta: <3 cm diameter
appendix: on CT <6 mm caliber
adults: <3 mm
children: <5 mm
azygous vein: on erect chest x-ray <10 mm diameter
bladder wall: <3 mm (well-di...
Obesity is defined as a body mass index (BMI) greater than 30 kg/m2. It is described as being a "modern epidemic" due to increased rates of metabolic syndrome and other complications in these patients, along with a high and increasing prevalence.
Obesity rates vary around the wor...
Obstruction of nasolacrimal drainage apparatus results in epiphora and can be primary or secondary, congenital or acquired. Obstruction can occur at canalicular, lacrimal saccular, or nasolacrimal ductal (post-saccular) levels.
Causes of obstruction
persistence of the m...
An obstructive uropathy is a catch-all term encompassing any cause of complete or partial, congenital or acquired and permanent or intermittent obstruction to the urinary tract. Depending on the severity of obstruction and extent, it may result in permanent change in both the collecting system p...
Occult fractures are those that are not visible on imaging, most commonly plain radiographs and sometimes CT, either due to lack of displacement or limitations of the imaging study. There may be clinical signs of a fracture without one actually being seen. MRI or nuclear medicine studies are som...
Ocular metastases, also termed uveal metastases, account for over 80% of all ocular pathology, and need to be distinguished from extraocular metastasis, which are a quite different group of tumors.
This article will discuss metastatic lesions affecting the orbits. For other intracranial metasta...
Ocular pathology covers a wide range of conditions and therefore represents the cause of a wide range of symptoms, signs and radiographic features.
Ocular metastases account for over 80% of all ocular pathology. With regard to the remainder of ocular lesions, the primary differentiating factor ...
Odontohypophosphatasia is the mildest form of hypophosphatasia that manifests as tooth dysplasia and/or early loss of deciduous or permanent teeth.
As with all forms of hypophosphatasia, the underlying abnormality is a mutation in the ALPL gene that encodes for tissue non-specific al...
Esophageal dysmotility refers to the pathological disruption of the normal sequential and coordinated muscle motion of the esophagus to transport food from the oropharynx to the stomach. It is an umbrella term used to refer to the common pathophysiological endpoint of dysmotility that can be cau...
Esophageal wall thickening can be observed in a number of situations and can be either focal or diffuse. It may be physiological, and can also be due to benign or malignant disorders.
diffuse esophageal spasm
forms of esophagitis
diffuse esophageal intramural hemat...
Oligohydramnios refers to a situation where the amniotic fluid volume is less than expected for gestational age. Often these fetuses have <500 mL of amniotic fluid.
The estimated prevalence can be up to ~6% of pregnancies 4.
The causes of oligohydramnios are pr...
Oligometastases refers to distant disease that is limited in number and distribution, Niibe et al. defined this as ≤5 metastatic/recurrent lesions with control of the primary lesion 1,2. These metastases can be treated with local measures (surgery, radiation therapy, etc.) with the aim of increa...
Omental cake refers to infiltration of the omental fat by material of soft-tissue density. The appearances refer to the contiguous omental mass simulating the top of a cake. Masses on the peritoneal surfaces and malignant ascites may also be present.
The most common cause is metasta...
Omphalomesenteric fistula occurs as a result of failure of obliteration of the omphalomesenteric duct. It is one of the congenital fistulas of the gastrointestinal tract.
The treatment of choice is often a partial transumbilical resection with umbilical restitution.
Open reduction-internal fixation, commonly abbreviated to ORIF, refers to the orthopedic operative management of a fracture (or fracture-dislocation complex) where reduction requires surgical (hence open) approach and internal fixation is applied.
Internal fixation may be in the form of:
Ophthalmoplegia describes the abnormal eye movement that occurs because of paralysis of one or more of the six extraocular muscles involved in eye movements. Classification can be based on the cause of the ophthalmoplegia or the directions of the affected movements.
There are numerous causes of...
Enlargement of the optic nerves is uncommon and has a surprisingly broad differential:
optic nerve glioma
optic nerve meningioma
Several cystic and cyst-like orbital lesions may be encountered in imaging of the orbits:
developmental orbital cysts
dermoid: commonest benign orbital tumor in childhood
congenital cystic eye
lacrimal gland ...
The differential diagnosis of orbital inflammatory diseases (including orbital pseudotumors) can be divided based on their location into:
dacryoadenitis of lacrimal glands
myositis of extraocular muscles
perineuritis of optic nerve
An orbital mass carries a relatively wide differential:
lacrimal gland or duct tumors
rhabdomyosarcoma of the orbit
optic nerve meningioma
optic nerve glioma
optic nerve schwannoma
developmental orbital cysts 3:
Orbital vascular lesions may be difficult to distinguish on imaging. However, the following conditions have been described:
lymphangioma / lymphangiovenous malformation / venolymphatic malformation
orbital venous malformat...
Osteoarthritis of the vertebral column, also known as spondylosis deformans, is common and usually merely referred to as spinal "degenerative change". Complications such as spinal stenosis are important to recognize.
The hallmark of osteoarthritis in the spine, as is the...
Elbow involvement in osteochondritis dissecans is rare. It is defined as a localized fragmentation of bone overlying the capitellum cartilage. For a general discussion of osteochondritis dissecans refer to the parent article - osteochondritis dissecans.
Most commonly seen in young...
Osteochondrosis is the descriptive term given to a group of disorders that affect the progress of bone growth by bone necrosis. It is only seen in children and adolescents who are still growing.
The commoner examples include:
The differential diagnosis for osteoid lesions includes:
bone island (enostosis)
associations: osteopoikilosis, osteopathia striata, melorheostosis
Osteophyte induced adjacent pulmonary atelectasis and fibrosis are typically seen as focal pulmonary interstitial opacities adjacent to thoracic spinal osteophytes. They can be a relatively common finding in thoracic CT imaging.
They are more common in older individuals.
Osteoporosis circumscripta cranii (also known as osteolysis circumscripta) refers to discrete radiolucent regions of the skull on plain radiographs. They are often seen in context of the lytic (incipient-active) phase of Paget disease of the skull, but may be observed in other circumstances as w...
The differential for osteoporosis includes:
mastocytosis (mast cells produce heparin)
Ovarian cystic neoplasms can be either benign or malignant and can arise from epithelial, stromal, or germ cell components. In general, the risk of malignancy in unilocular cystic tumors <10 cm in women over the age of 50 years is thought to be low 3-4.
ovarian mature cystic teratoma
A hypointense ovarian lesion on T2 weighted MRI is usually a sign of benignity. The low signal is considered to be due to fibrosis and blood products 1.
Lesions that can give this appearance include 1:
Ovarian tumors are relatively common and account for ~6% of female malignancies. This article focuses on the general classification of ovarian tumors. For specific features, refer to the subarticles.
Primary ovarian tumors
Surface epithelial-stromal ovarian tumors (60-70%)...
There are several ovarian tumors associated with endometrial thickening and is often due to oestrogenic effects of the ovarian tumor.
Such tumors include:
ovarian epithelial tumors
endometroid carcinoma of the ovary
may have synchronous endometrial carcinoma or endometrial hyperplasia, prese...
Oxalosis is supersaturation of calcium oxalate in the urine (hyperoxaluria), which in turn results in nephrolithiasis and cortical nephrocalcinosis.
This article focus on the secondary oxalosis, please refer to primary oxalosis for a specific discussion on this entity.
The differential diagnosis of pediatric cervical lesions is commonly encountered in practice, unfortunately, the list is long.
Most lesions tend to be inflammatory 3:
nontuberculous mycobacterial lymphadenitis
The clavicle is a unique bone and as such it often displays unique pathology. The following is an attempt to summarize pediatric clavicle abnormalities.
Pediatric bone tumors and tumor-like lesions of the clavicle
majority of clavicular tumors are malignant
Ewing sarcoma (most common)
Pediatric nasal cavity masses can occur within the nose or the nasopharynx. These masses are often found incidentally on imaging but can be readily apparent clinically.
The clinical features of these lesions tend to mimic upper respiratory processes and may result in dela...
Pediatric renal tumors 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 tumor: common in older children 1-8 years old
There is a wide range of primary malignancies that results in pediatric skeletal metastases 1:
leukemia: although not truly metastases
clear cell sarcoma: Wilms’ variant
Ewing’s sarcoma: lung metastases much more common
Pancreatic atrophy is non-specific and 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 ...
Pancreatic calcifications can arise from many etiologies.
Punctate intraductal calcifications
alcoholic pancreatitis (20-40%) 2
intraductal, numerous, small, irregular
preponderant cause of diffuse pancreatic intraductal calcification
gallstone pancreatitis (2%) 2
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...
Pancreatitis (plural: pancreatitides) refers to inflammation involving the pancreas.
It has various forms which can be classified in many many ways according to time of onset, etiological agent or associated pathology.
interstitial edematous pancreatitis
A pantaloon hernia (dual hernia, Romberg 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 by t...
Papillary lesions of the breast comprise a wide group and range from 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 papilloma of the b...
Paralabral cysts are type of cyst located adjacent to a cartilage labrum of large joints. They are typically described in the shoulder and hip. Please refer to the sub-articles of discussion of these.
paralabral cyst of the shoulder
paralabral cyst of the hip
Parasyndesmophytes or floating syndesmophytes are, as the name suggests, paravertebral dystrophic soft tissue calcifications or heterotopic ossifications.
They are known to be seen in psoriatic arthritis and reactive arthritis 4.
Initially they begin at a dist...
Paratesticular lesions have a long list of differential diagnoses:
epididymal cyst (most common epididymal mass)
adenomatoid tumor (most common epididymal tumor)
scrotal tunica cysts
tunica vaginalis cyst
tunica albuginea cyst
A paratesticular mass may derive from a number of structures that surround the testicle within the scrotum; most commonly, they derive from the spermatic cord.
The masses can be categorized as benign (70%) or malignant (30%).
spermatic cord lipoma (most common par...
Parkinson-plus syndrome refers to a loose group of neurodegenerative disorders that are characterized by features of Parkinson disease but with other neurological symptoms/signs. They have a poor response to levodopa, and mostly have fairly characteristic neuroimaging features.
Parotid enlargement (also known as parotidomegaly) has a wide differential given the significant breadth of pathology that can affect the parotid gland. These can be separated by the standard surgical sieve approach into infective, inflammatory, immune, neoplastic, infiltrative, and congenital c...
Passive atelectasis, also known as relaxation atelectasis, refers to a form of lung atelectasis due to loss of the negative pressure state in the pleural space. With a loss of the negative intrapleural pressure, the lung is no longer held against the chest wall and is said to relax back to its n...
Patella alta, or a high riding patella, describes a situation where the position of the patella is considered high. It may be idiopathic or may result secondary to a patellar tendon rupture.
Several conditions are known to be associated with patella alta, including:...
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 in...
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 tumors are extremely rare. They can be either benign or malignant primary bone tumors, or metastases.
Patellar tumors represent just 0.1% of all primary bone tumors 1.
Patients may present with anterior knee pain and/or a palpable mass 1,3.
Some medical conditions are characterized by the presence of pathological gas i.e. gas/air found in a space, tissue, or organ, where it would not normally be expected to be.
prefix 'pneumo' is common, especially when it refers to gas within a body space/cavity e.g. pneumothorax
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 ischemic 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 teardrop-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 inc...
A pedunculated intratracheal mass has a variety of differential diagnoses:
benign tumor, 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 pseudoarticulations. 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-gynecological masses, e.g. colorectal carcinom...
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 tumors are those that arise within 2 cm of the ampulla of Vater in the duodenum.
Tumors that fall under this group include four main types of tumors 1,4 that will be approached in their specific articles:
pancreatic head/uncinate process tumors: includes pancreatic ductal adenoca...
Periapical radiolucencies are commonly observed findings in OPG and other dental / head and neck imaging modalities.
They can represent a number of pathologies:
periapical lucency related to apical periodontitis
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)
Peribronchovascular thickening is a broad imaging descriptive term usually used to describe thickening of any or a combination of the below:
peribronchovascular interstitial thickening
bronchial wall thickening: can be differentiated from true peribronchovascular thickening on cross-sectional ...
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 radio...
Pericardial fat pads are normal structures that lie in the cardiophrenic angle. They are adipose tissues surrounding the heart composed of the epicardial fat, which lies between the myocardium and visceral pericardium, and paracardial fat, which is adherent and external to the parietal pericardi...
Perifissural lung nodules (PFNs) are a type of intrapulmonary nodules that, most of the times, represent pulmonary lymph nodes.
Although perilymphatic pulmonary nodules can also be perifissural in distribution, they should be distinguished from PFNs, as they are usually associate...
Perigestational hemorrhage refers to hemorrhage that occurs around the fetus during the gestational period. The spectrum of hemorrhage includes:
chorionic hemorrhage: caused by the separation of the chorion from the endometrium
subchorionic hemorrhage: most common type, occurs between the cho...
Perilymphatic lung nodules follow perilymphatic channels and on imaging are typically subpleural, occur along fissures, interlobular septa and adjacent to the bronchovascular bundles.
Lung nodules in a perilymphatic distribution can be seen in association with a number o...
Perinephric fluid collections are commonly seen after renal transplantation. The appearance of a perinephric fluid collection is often nonspecific but may be partially differentiated by when the transplant occurred.
Early post-transplant period (<4 weeks)
Periosteal reaction in the pediatric 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 characterized 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
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.
Dependent on the definition, the incidence of enlarged peroneal tubercle has been reported to be from 20.5 - 24% 2.
Two bony projections or protuberances may be se...
It is important to have a systematic way of approaching a case with per vaginal bleeding in the exam.
intrauterine fetal demise
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:
asymmetrical marrow / asymmetrical pneumatization
fat signal intensity on all sequences
petrous apex cephalocoele 4
CSF signal intensity on all sequences
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.