Osteoradionecrosis (ORN) refers to a severe delayed radiation-induced injury and is characterized by bone tissue necrosis and failure in healing. There is some overlap with the term radiation osteitis.
Microvascular damage is thought to result in altered blood supply to the bone. Th...
Osteosarcomas are malignant bone-forming tumors. They are the second most common primary bone tumor after multiple myeloma, accounting for ~20% of all primary bone tumors. They can be classified into primary and secondary forms, as well as histologic types, of which conventional osteosarcoma is ...
Osteosclerosing (or osteosclerotic) myeloma is an uncommon form of multiple myeloma. It may manifest as multiple sclerotic lesions or areas of diffuse osteosclerosis 3. It once was considered in the same spectrum of plasma cell dyscrasias with polyneuropathy as POEMS syndrome but is now consider...
An osteotomy refers to an orthopedic surgical procedure that involves a bone to shorten or lengthen it or to change its alignment.
It can by performed at many sites.
Examples include :
Bernese osteotomy - Ganz osteotomy
The ostiomeatal complex (OMC) or ostiomeatal unit (OMU), sometimes less correctly spelled as osteomeatal complex, is a common channel that links the frontal sinus, anterior ethmoid air cells and the maxillary sinus to the middle meatus, allowing airflow and mucociliary drainage.
Some ostiomeatal complex anatomical variations, which do not cause disease by themselves, can promote narrowing and even obstruction 1:
concha bullosa ~10% (range 4-15%) - aerated middle turbinate
intralamellar cell: air cell within vertical portion of the middle turbinate
A useful mnemonic to remember the five parts of the ostiomeatal complex is:
H: hiatus semilunaris
E: ethmoidal bulla
M: maxillary ostium
U: uncinate process
Emus have large beaks, and hence could have large ostiomeatal complexes (if they had paranasal sinu...
The Ostmann fat pads (also known as Ostmann fatty bodies) are located inferomedial to the Eustachian tubes and are thought to be important in normal closure, preventing transmission of nasopharyngeal pressure to the middle ear. Failure to visualize this thin triangular fat pad is a feature of pa...
The os trigonum (plural: os trigona) is one of the ossicles of the foot and can be mistaken for a fracture.
It sits posterior to the talus on the lateral foot radiograph and represents a failure of fusion of the lateral tubercle of the posterior process. It is estimated to be present in ~7% of...
An os vesalianum is an accessory ossicle of the foot. Although asymptomatic, it may become symptomatic occasionally, causing lateral foot pain and requiring surgical excision 2.
It is formed as a result of failed fusion of the secondary ossification center of the metatarsal. It i...
The os triangulare (also known as the os intermedium antebrachii or os triquetrum secundarium) is an accessory ossicle located between the ulnar styloid, lunate and triquetrum 1,2.
They may be unilateral or bilateral and the main differential diagnosis is non-union of an ulnar styloid process f...
The otic capsule or osseous (bony) labyrinth refers to the dense bone of the petrous temporal bone that surrounds the membranous labyrinth of the inner ear. It is surrounded by the less dense and variably pneumatized petrous apex and mastoid part of the temporal bone.
From anterior to posterior...
The otic ganglion is one of four parasympathetic ganglia of the head and neck. It receives parasympathetic fibers from the glossopharyngeal nerve.
small and disc shaped
located in the infratemporal fossa
it lies immediately below the foramen ovale, medial to the mandibular divi...
Otitis externa refers to inflammation of the external ear.
It is quite a common condition and may affect up to 10% of people during their lifetime.
It can present in several forms:
acute otitis externa
chronic otitis externa
necrotizing otitis externa
Otitis media refers to inflammation or infection of the middle ear cavity.
The specific type of otitis media depends on various clinical findings and setting:
acute otitis media: acute infection of the middle ear
otitis media with effusion: middle ear fluid without signs or sympt...
Otomastoiditis, or more simply inflammation of the mastoid air cells, can be divided into two distinct entities:
acute otomastoiditis: usually due to bacterial infection
chronic otomastoiditis: usually due to Eustachian tube dysfunction
Otopalatodigital syndrome type I is a rare genetic disorder characterized by:
and a characteristic face (with hypertelorism, broad nasal root, prominent supraorbital ridges, small flat nose and downslanted palpebral fissures).
It is a member of ...
Otorrhagia denotes hemorrhage from the external acoustic meatus and is commonly seen in the setting of petrous temporal bone fractures or soft tissue injuries to the external or middle ear. Rarely an internal carotid artery aneurysm with dehiscence into the middle ear can present with spontaneou...
Otosclerosis, also known as otospongiosis, is a primary osteodystrophy of the otic capsule (bony labyrinth of the inner ear). It is one of the leading causes of deafness in adults.
The term otosclerosis is somewhat of a misnomer. Much of the clinical course is characterized by luce...
Otosyphyilis, otic syphilis or syphilitic labyrinthitis is a manifestation of neurosyphilis affecting the inner ear.
For a general discussion, and for links to other system-specific manifestations, please refer to the article on syphilis.
The pathological features of syphilitic lab...
The Ottawa ankle rules are a clinical decision-making strategy for determining which patients require radiographic imaging for ankle and midfoot injuries. Proper application has high (97.5%) sensitivity and reduces the need for radiographs by ~35% 1,2,4.
There are two components, assessing for...
The Ottawa knee rules are a clinical decision-making strategy for determining which patients require radiographic imaging for knee pain.
A patient with knee pain qualifies for knee radiographs if any of the following apply:
55 years or older
point tenderness at the fibular head
An outbreak is an epidemiological term used to describe the sudden occurrence of a disease or condition in patterns greater than those expected in a specific geographical area at a specific time. The term is not exclusively used for infectious diseases, e.g. in 1986, the Chernobyl nuclear reacto...
Out of field artifact (also known as incomplete projection artifact) is due to part of the patient existing peripheral to the field of view of the CT scanner. This can be a particular issue in obese patients who only just fit within the scanner bore.
The lack of data from these out of field tis...
The output phosphor is a component of the image intensifier in fluoroscopic systems that converts the energy from the electrons into light photons. In an II, the large number of light photons produced are subsequently captured by various imaging devices to produce a visible image.
The oval window (or fenestra vestibuli) is a kidney-shaped aperture in the medial wall of the mesotympanum of the middle ear, providing communication with the vestibule of the inner ear. The footplate of the stapes is attached to its rim by the annular ligament 1.
The variability of the size o...
Oval window atresia or congenital absence of oval window shows absent cleavage plane between the lateral semicircular canal above and cochlear promontory below associated with anomalous stapes and malpositioned facial nerve (cranial nerve VII).
Profound conductive hearin...
An ovarian adenofibroma is a type of ovarian epithelial tumor. Many authors however overlap this entity with an ovarian cystadenofibroma and consider these tumors often as part of an adenofibroma - cystadenofibroma spectrum.
Adenofibromas are benign compound tumors composed of interm...
The Ovarian-Adnexal Reporting and Data System Magnetic Resonance Imaging (O-RADS MRI) forms the MRI component of the Ovarian-Adnexal Reporting and Data System (O-RADS). This system aims to ensure that there is a uniform, unambiguous MRI evaluation of ovarian or other adnexal lesions, accurately ...
The Ovarian-Adnexal Imaging Reporting and Data System, (O-RADS), aims to ensure that there are uniform unambiguous sonographic and MRI evaluations of ovarian or other adnexal lesions, accurately assigning each lesion to a risk category of malignancy being present, and which informs the appropria...
The Ovarian-Adnexal Reporting and Data System Ultrasound (O-RADS US) forms the ultrasound component of the Ovarian-Adnexal Reporting and Data System (O-RADS). This system aims to ensure that there are uniform unambiguous sonographic evaluations of ovarian or other adnexal lesions, accurately ass...
The ovarian artery is a paired structure and is the main gonadal artery in females.
The ovarian artery arises anterolaterally from the aorta just inferior to the renal arteries and superior to the inferior mesenteric artery (between L2 and L3).
Descends caudally ...
Ovarian borderline mucinous cystadenomas are a subtype of ovarian mucinous tumors and, as the name stands, are intermediate between mucinous cystadenomas and mucinous cystadenocarcinomas.
They account for ~ 10-15% of all ovarian mucinous tumors.
They are microscopicall...
The most commonly adopted ovarian cancer staging system is the FIGO staging system. The most recent staging system is from 2014 1:
CT is considered the best imaging modality for staging ovarian cancer. 4.
stage I: tumor limited to the ovaries
tumor limited to one ovary
Ovarian carcinoid tumors are very rare sub type of ovarian tumor. They are usually classified under ovarian germ cell tumors (monodermal teratoma 5). The term carcinoid tumor of the ovary can be used to described primary ovarian carcinoid tumors or metastatic carcinoid tumors to the ovary. The f...
Ovarian choriocarcinoma is a rare sub type of ovarian germ cell tumor.
They account for less than 1% of ovarian tumors.
In pre-menarchal patients, the tumors manifest with iso-sexual precocity (approximately 50% of cases) and other symptoms associated with...
Ovarian collision tumors are an uncommon ovarian neoplasm where there is co-existence of two adjacent but histologically distinct tumors in an ovary with no histologic admixture at the interface.
The exact pathogenesis is not well known. They are most commonly composed of ovarian ter...
Ovarian cysts are commonly encountered in gynecological imaging and vary widely in etiology from physiological to complex benign to neoplastic.
Small cystic ovarian structures should be considered normal ovarian follicles unless the patient is pre-pubertal, post-menopausal, pregnant,...
An ovarian cystadenocarcinofibroma (CACF) is an extremely rare ovarian tumor. The tumor has a fibrous component is considered as the malignant counterpart of an ovarian cystadenofibroma (CAF) 1. There is very little literature on the imaging findings of these.
Ovarian cystadenofibromas are a relatively uncommon benign epithelial ovarian tumor where the fibrous stroma remains a dominant component of the neoplasm. As a group, they are thought to represent ~1.7 % of all benign ovarian tumors 3.
Lesions can be bilateral in ~15% of cases. Altho...
Ovarian cystadenoma is a broad term given to a certain types of ovarian epithelial tumors. This can include
ovarian serous cystadenoma
ovarian borderline serous cystadenoma
ovarian mucinous cystadenoma
ovarian borderline mucinous cystadenoma
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
Ovarian dysgerminomas are a type of germ cell tumor of the ovary. They are the most common malignant germ cell tumors of the ovary and are thought to account for ~1% of all ovarian neoplasms 5.
They are rare ovarian tumors that occur predominantly in young women (majority occurrin...
Ovarian ectopic pregnancies are rare when compared to other types of ectopic pregnancy such as tubal ectopic.
The ovary is the anatomic site of less than 3% of ectopic pregnancies 5.
Patients present with abdominopelvic pain during the first trimester (usu...
Ovarian embryonal carcinomas are rare and malignant germ cell tumors of the ovary.
It is found predominantly in children and adolescents (average age 14 years).
Precocious puberty or menstrual irregularity occurs in 60% 2. The tumor can secrete beta-hCG and...
Ovarian fibromas are a benign ovarian tumor of sex cord / stromal origin. Although fibromas account for ~4% of all ovarian neoplasms, they are the most common sex cord ovarian tumor.
Fibromas occur at all ages but are most frequently seen in middle-aged women.
Ovarian fibromatosis (OF) refers to a rare benign phenomenon where there is tumor-like ovarian enlargement due to diffuse ovarian fibrosis.
It may have a predilection towards younger pre-menopausal females (age range around 13-39 years) with a mean age of presentation of 25 years ...
Ovarian fibrosarcoma is a malignant mesenchymal fibroblastic tumor of the ovary that has multiple mitotic figures which is the most important factor in histopathological diagnosis (4 or more mitotic figure per 10 high power fields).
Ovarian fibrosarcoma is a very rare malignant o...
Ovarian fibrothecomas comprise tumors in the spectrum of ovarian sex cord / stromal tumors where there are components of both an ovarian fibroma and an ovarian thecoma.
Most occur in adult women, with ~66% in postmenopausal women. Although they account for ~1% of all ovarian tumo...
An ovarian follicle (also known as a Graafian follicle in its mature state) is the basic unit of female reproductive biology and is composed of roughly spherical aggregations of cells and contains a single oocyte.
An ovarian follicle can be initiated to grow and develop, culminat...
An ovarian follicular cyst is type of simple physiological ovarian cyst.
The terms "ovarian cyst" and "ovarian follilcular cyst" are often used interchangeably. These two terms describe lesions >3 cm, and it is important to differentiate them from an "ovarian follicle" which is <3 ...
Ovarian hyperstimulation syndrome (OHSS) is a complication of ovarian stimulation treatment (ovarian induction therapy) for in vitro fertilisation. Rarely, it may also occur spontaneously in pregnancy (see below). It consists of ovarian enlargement with extravascular accumulation of fluid leadin...
Ovarian hyperthecosis (OHT) is a condition where there is a presence of luteinized thecal cells within a hyperplastic ovarian stroma.
Clinical manifestations include hyperandrogenism, obesity, hypertension, and impaired glucose tolerance. Virilization has been reported to...
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:
The ligament of the ovary, utero-ovarian ligament or ovarian ligament, is one of the supporting ligaments of the ovary and uterus within the female pelvis. It should not to be confused with the suspensory ligament of the ovary, which is a separate structure that extends laterally from the ovary....
Ovarian lymphoma can refer to
primary involvement of the ovaries with lymphoma (i.e. primary ovarian lymphoma): very rare
secondary ovarian involvement of the ovaries with generalized lymphoma (i.e. secondary ovarian lymphoma): more common scenario
Mucinous cystadenocarcinoma of the ovary is a rare malignant ovarian mucinous tumor. This type can account for 5-10% of all ovarian mucinous tumors. It is a type of ovarian epithelial tumor.
Retrospective studies have suggested that many mucinous carcinomas initially diagnosed as pr...
Mucinous cystadenoma of the ovary is at the benign end of the spectrum of mucin-containing epithelial ovarian tumors.
The estimated peak incidence is at around 30-50 years of age.
They comprise approximately 80% of mucinous ovarian tumors and 20-25% of all benign ovarian tumors....
Ovarian mucinous tumors are a subgroup of ovarian epithelial tumors. They represent 10-15% of all ovarian tumors and ~10% of all malignant ovarian tumors. They are subdivided according to their malignant potential and clinical behavior into:
ovarian mucinous cystadenoma
ovarian borderline muci...
Ovarian serous cystadenocarcinoma is the malignant form of ovarian serous tumor, the most common type of ovarian epithelial tumor. It is the most common type of ovarian malignancy.
Increasingly, high-grade serous carcinoma and low-grade serous carcinoma are recognized as distinct tumor types ra...
Ovarian serous cystadenomas are a type of benign ovarian epithelial tumor at the benign end of the spectrum of ovarian serous tumors.
Serous ovarian tumors are traditionally described with a "cyst-" prefix because of their primarily cystic composition, e.g. cystadenoma, cystadenoca...
Ovarian serous neoplasms are the commonest of four general types of the epithelial ovarian tumors, and are more prevalent than the mucinous ovarian tumors.
Serous ovarian neoplasms are subdivided into benign, borderline, and malignant lesions according to their malignant potential and clinical ...
Ovarian Sertoli-Leydig cell tumors (SLCT), also known as ovarian androblastomas, are a subtype of ovarian sex cord-stromal tumor.
They are rare and only account for ~0.5% of all ovarian tumors. While they can present at any age, they typically present <30 years old, with a mean ag...
Ovarian teratomas are the most common group of ovarian germ cell tumors.
They can be divided into 3 main sub types
mature ovarian teratoma
immature ovarian teratoma
struma ovarii tumor
Ovarian thecomas are benign ovarian tumors of sex cord / stromal (mesenchymal) origin. They are thought to account for approximately 0.5-1% of all ovarian tumors. As ovarian thecomas secrete estrogen, they are described as functional ovarian tumors.
They typically present in older...
Ovarian torsion, also sometimes termed adnexal torsion or tubo-ovarian torsion, refers to rotation of the ovary and portion of the fallopian tube supplying the vascular pedicle.
It can be intermittent or sustained and results in venous, arterial and lymphatic stasis. It is a gynecological emer...
Ovarian transposition is a surgical procedure in which the ovaries are displaced from the pelvis before pelvic radiation therapy in order to protect them from radiation injury.
It is performed in premenopausal women with a variety of pelvic malignancies (e.g cervical cancer, rectal cancer, and ...
Ovarian tumors are relatively common and account for ~6% of female malignancies. This article focuses on the general classification of ovarian tumors. For specific tumor features, please refer to the relevant subarticles.
Primary ovarian tumors
Surface epithelial-stromal o...
There are several ovarian tumors associated with endometrial thickening and this is often due to oestrogenic effects of the ovarian tumor.
Such tumors include:
ovarian epithelial tumors
endometrioid carcinoma of the ovary
may have synchronous endometrial carcinoma or endometrial hyperplasia,...
Ovarian vein embolization is an interventional technique primarily used towards the treatment of varicosities.
The main indications are:
as part of management of pelvic congestion syndrome 1-4
to treat pelvic varicosities diagnosed by imaging
to treat labial and/or perineal vari...
Ovarian vein syndrome is a relatively rare condition where a dilated ovarian vein (ovarian venous varix) causes notching, dilatation, or obstruction of the ureter. This is usually secondary to varicosities of the ovarian vein or ovarian vein thrombosis and occurs at the point where the ovarian v...
Ovarian vein thrombosis (actually most often thrombophlebitis) occurs most commonly in postpartum patients and can result in pulmonary emboli. A presentation is usually with acute pelvic pain in the postpartum period, then termed puerperal ovarian vein thrombosis or postpartum ovarian vein throm...
Ovarian venous varix is a situation where there is variceal dilatation of the ovarian vein (usually left). It can be associated with pelvic congestion syndrome.
May be seen as a serpiginous structure adjacent to the aorta along the course of the ovarian vein.
Ovarian yolk sac tumors, also known as endodermal sinus tumors, are a type of ovarian germ cell tumors.
Ovarian yolk sac tumor is a rare malignant ovarian germ cell tumor that usually occurs around the second decade of life. It is considered the most common malignant germ cell tum...
The ovaries (TA: ovarium 9) are paired female gonads of the reproductive and endocrine systems. They lie within the ovarian fossa on the posterior wall of the true pelvis and form part of the adnexa.
The ovaries are firm and ovoid in shape and measure approximately 1.5-3.0 cm × ...
Overall visual assessment of coronary artery calcification is a simple scoring system for risk assessment of coronary heart disease mortality by an overall "gestalt" of none, mild, moderate or heavy coronary artery calcification. It is comparable to the Agatston score but has the advantage of be...
Overfitting is a problem in machine learning that introduces errors based on noise and meaningless data into prediction or classification. Overfitting tends to happen in cases where training data sets are either of insufficient size or training data sets include parameters and/or unrelated featu...
Fecal impaction is a sequela of long term constipation, whereby a hard fecal mass in the rectum prevents defecation from occurring. The resultant rectal dilatation leads to smooth muscle relaxation of the internal anal sphincter. Concurrently the obstructing stool mass leads to increased secreti...
Overlapping fetal fingers is an antenatal ultrasound observation where the fetal fingers are seen to overlap each other. It may be seen seen with a concurrent clenched fetal hand. If the hand is clenched typically the 2nd finger is seen to overlap the 3rd 4.
a well re...
The owl-eyes sign, also referred to as snake-eyes sign or fried-eggs sign, represents bilaterally symmetric circular to ovoid foci of high T2-weighted signals in the anterior horn cells of the spinal cord and is seen on axial MR imaging. The sagittal corollary is a "pencil-like" vertical linear ...
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.
Oxycephaly (also known as turricephaly) is the most severe of the craniosynostoses and results from the premature closure of all sutures.
Characterized by a tower-like skull which may be associated with:
8th cranial nerve lesion
optic nerve compression
Oxygen (chemical symbol O) is one of the basic organic elements, and is a constituent of most of the known organic molecules - and therefore all lifeforms - on earth.
Oxygen is a colourless odorless diatomic gas with an atomic number 8 and atomic weight 15.999. It h...
Oxygen masks are commonly visible on chest imaging, as they are generally not removed before the examination is performed.
Oxygen masks are of soft-tissue density and may mimic lung lesions. A nebuliser mask with liquid in its cup causing an air-fluid l...
p16 is a widely used immunohistochemical marker indicating expression of the cell cycle protein cyclin-dependent kinase inhibitor 2A, which is upregulated by human papillomavirus (HPV) infection. In the uterine cervix, p16 positivity supports the diagnosis of a high-grade squamous intraepithelia...
Pachydermoperiostosis (PDP) refers to a rare osteoarthrodermopathic 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.
Also known as Touraine-Solente-Golé syndrome, ...
Pacinian corpuscles, also known as lamellar corpuscles, are pressure-sensitive nerve endings in the hand. They are the largest mechanoreceptors in the body and are important to recognize as they may be mistaken for pathology.
Pacinian corpuscles are seen as ovo...
Paclitaxel lung toxicity is a form of drug induced lung disease that can precipitate following the use of paclitaxel which is a chemotherapeutic agent commonly used in the treatment of breast, ovarian, and non-small cell lung cancers.
Two forms have been described:
hypersensitivity reactions 1...
The AP supine abdominal radiograph is a routine view when imaging the pediatric abdomen. This view may be taken alongside the PA erect and lateral decubitus views. As radiation protection is an essential consideration in pediatrics, some departmental protocols may only perform one view (either t...
The invertogram view is an additional projection to demonstrate the pediatric abdomen and is often used exclusively in characterizing anal atresia. However, as this view may be less comfortable for the patient and result in a more technically challenging examination, a more ideal alternative tec...
The lateral decubitus radiograph is an additional projection for assessing the pediatric abdomen. This view is ideal for displaying free air in the abdomen and/or if the patient is unable to lie supine 1. As radiation dose is an important consideration for pediatric imaging, the lateral decubitu...
The PA erect abdominal radiograph is the standard view for assessing air-fluid levels and free air in the pediatric abdomen. This view may be taken alongside the AP supine and lateral decubitus views. As radiation protection is an essential consideration in pediatrics, some departmental protocol...
The prone cross-table lateral view is an additional projection to demonstrate the pediatric abdomen and is a more ideal alternative to the invertogram, which may be less comfortable for the patient. This discomfort may result in a continuously crying baby, causing the puborectalis sling to contr...