≤11 ribs is associated with a number of congenital abnormalities and skeletal dysplasias, including:
Down syndrome (trisomy 21)
asphyxiating thoracic dysplasia (Jeune syndrome)
short rib polydactyly syndromes
chromosome 1q21.1 deletion...
Abnormally thickened endometrium on imaging may occur for a number of reasons which may be categorized based on whether or not they are related to pregnancy. Etiologies may also be classified based on whether the patient is premenopausal or postmenopausal.
Abnormal testicular Doppler flow (arterial, venous, or both) can be a differential challenge. Always remember that the patient's presenting history helps quite a bit in narrowing the differential.
partial testicular torsion (<360 degrees)
venous outflow is obstructed first, resul...
Non-visualization of the fetal stomach on ultrasound can occur with various physiological as well as pathological processes. It becomes a significant sonographic observation >14 weeks of gestation (about the time the fetus begins to swallow).
physiological emptying: transient
Achilles tendon thickening can occur for a number of reasons.
The Achilles tendon has an average AP diameter of 6 mm 1. Thickening of the tendon is when it exceeds 8 mm in AP diameter and can result from:
Acro-osteolysis (plural: acro-osteolyses) refers to resorption of the distal phalanx. The terminal tuft is most commonly affected. It is associated with a heterogeneous group of pathological entities and, some of which can be remembered by using the mnemonic PINCH FO.
When there is linear bone ...
Acute airspace opacification with lymphadenopathy is a subset of the differential diagnosis for generalized airspace opacification and includes:
post-obstructive causes (usually chronic, but 'new' changes can occur)
primary lung cancer
Acute bilateral airspace opacification is a subset of the larger differential diagnosis for airspace opacification. An exhaustive list of all possible causes of acute bilateral airspace opacities is long, but a useful way to consider the huge list is via the material within the airways:
Acute unilateral airspace opacification is a subset of the differential diagnosis for airspace opacification.
The exhaustive list of all possible causes would be huge, but a useful framework includes:
pus, i.e. pulmonary infection
Adrenal calcification is not a rare finding in healthy asymptomatic people and is usually the result of previous hemorrhage or tuberculosis. Addison disease patients only occasionally develop calcification.
sepsis: Waterhouse-Friderichsen syndrome
Cervical lymphadenopathy in an adult can result from a vast number of conditions. They include:
from head and neck tumors
other neoplastic lesions
Air space opacification is a descriptive term that refers to filling of the pulmonary tree with material that attenuates x-rays more than the surrounding lung parenchyma. It is one of the many patterns of lung opacification and is equivalent to the pathological diagnosis of pulmonary consolidati...
The differential for air space opacities is extensive, and needs to be interpreted in context of chronicity (previous imaging) and clinical context. It is therefore useful to divide airspace opacities as follows:
acute airspace opacities with lymph node enlargement
acute airspace opacities: un...
Mammographic screening detects early breast cancers and thereby reduces potential mortality. However, its sensitivity is inversely related to breast density 1.
Altered density between two mammograms can arise in a number of situations:
Affecting both breasts:
interval commencement/cessation ...
Alternating radiolucent and radiodense metaphyseal lines can be seen with a number of conditions and the differential diagnosis is wide:
growth arrest lines
rickets: especially those on prolonged treatment, e.g. vitamin D dependent rickets
Amorphous calcifications, previously known as indistinct calcifications, are a morphological descriptor for breast calcifications that are small and/or hazy such that no clearly defined shape/form can be ascribed.
Many benign and malignant conditions may be seen in association with ...
Anterior knee pain is common with a variety of causes which can be divided anatomically using a layered approach1 from superficial to deep:
Superficial soft tissues
quadriceps tendinosis / partial tear
Anterior vertebral body beaking occurs in a number of conditions and may emanate from the central portion or the lower third of the vertebral body.
Morquio syndrome 1 (middle for Morquio)
Hurler syndrome 2
Apical pleural cap refers to a curved density at the lung apex seen on chest radiograph.
The frequency of apical pleural thickening increases with age 3.
It arises from a number of causes:
idiopathic: chronic ischemic etiology is favored f...
The apple core sign, also known as the napkin ring sign (bowel), is most frequently associated with constriction of the lumen of the colon by a stenosing annular colorectal carcinoma.
The appearance of the apple-core lesion of the colon also can be caused by other diseas...
Dilatation of the ascending aorta is a common finding in the elderly but unusual in younger patients.
In adults, an ascending aortic diameter greater than 4 cm is considered to indicate dilatation 4. Aneurysmal dilatation is considered when the ascending aortic diameter reaches or ex...
Asymmetry in breast size can arise from a number of factors.
Breasts are rarely absolutely the same size or volume. Normal variation is common. Most females have slight discrepancies in breast size. Asymmetric progressive breast enlargement is unusual but known. The role of the breas...
Asymmetries in mammography represents a spectrum of morphological descriptors for a unilateral fibroglandular-density finding seen on one or more mammographic projections that does not meet criteria for a mass. The term refers to a density finding and should not be confused with asymmetry in bre...
Band like structures in the gestational sac is not an uncommon finding in the first trimester or second trimester ultrasound scans and can represent a number of varying conditions
Basal ganglia and thalamus signal abnormalities occur in a wide variety of conditions. Ischemia/hypoxia, metabolic disorders and toxins, particularly those that affect the respiratory chain, have a predilection for affecting the basal ganglia as they are highly metabolically active.
They can b...
Basal ganglia calcification is common and is seen in approximately 1% of all CT scans of the brain, depending on the demographics of the scanned population. It is seen more frequently in older patients and is considered a normal incidental and idiopathic finding in an elderly patient but should ...
There are many causes of basal ganglia T1 hyperintensity, but the majority relate to deposition of T1-intense elements within the basal ganglia such as:
calcium and phosphate abnormalities
acquired non-wilsonian hepatocerebral degeneration
The causes of basal ganglia T2 hyperintensity can be remembered using the mnemonic LINT:
venous infarction (internal cerebral vein thrombosis)
neurodegenerative / metabolic
autoimmune encephalitis (e.g. anti-D2 dopamine antibody encephalitis)
Basal ganglia T2 hypointensities can be caused by any of the following and is commonly remembered using the mnemonic ChOMP.
Parkinson disease: more in globus pallidus
Parkinson-plus syndrome: more in putamen
deoxyhemoglobin of hemorrhage
Basilar invagination, also called basilar impression, is a congenital or acquired craniocervical junction abnormality where the tip of the odontoid process projects above the foramen magnum.
The terms basilar invagination and basilar impression are often used interchangeably becau...
Bat wing or butterfly pulmonary opacities refer to a pattern of bilateral perihilar shadowing. It is classically described on a frontal chest radiograph but can also refer to appearances on chest CT 3,4.
Bat wing pulmonary opacities can be caused by:
pulmonary edema (es...
Benign lytic bone lesions encompass a wide variety of entities. A useful starting point is the FEGNOMASHIC mnemonic.
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The differential for bilaterally enlarged adrenal glands is relatively limited:
micronodular adrenal hyperplasia
macronodular adrenal hyperplasia
adrenocorticotropin (ACTH)-independent macronodular adrenocortical hyperplasia (AIMAH) 2
Bilateral axillary lymphadenopathy can result from a number of causes and generally implies a systemic process. They include:
autoimmune diseases, e.g.:
systemic lupus erythematosus (SLE)
Involvement of both middle cerebellar peduncles is uncommon, but has a relatively long list of differential diagnoses, including 1:
multiple systemic atrophy (MSA)
Bilateral renal enlargement can arise from a number of causes which include 1:
diabetic nephropathy (common)
renal involvement with lymphoma
acute interstitial nephritis
vasculitis / autoimmune
autosomal recessive polycystic kidneys (ARPKD)
adult dominant polycys...
Bilateral testicular lesions have a relatively limited differential diagnosis.
lymphoblastic leukemia (acute or chronic)
primary testicular lymphoma is rare but the testes are often the site of lymphoma/leukemia recurrence due to ...
Bile duct dilatation can be due to several etiologies.
Variable, depending on underlying cause, but usually:
right upper quadrant pain
Harmonic imaging is useful when assessing the biliary system, as it improves the clarity o...
Thickening of the bile duct wall can stem from a variety of etiologies.
bile duct wall thickening
bile duct walls are typically not visible when normal
possible narrowing of the ducts with obstruction
possible secondary signs of cholangitis, including debri...
Differential diagnosis for bladder wall thickening depends on whether the bladder is adequately distended. The bladder wall may be thickened if:
>3 mm when distended
>5 mm when nondistended
If the bladder is not distended, then it is difficult to exclude artifactual thickening from a collapse...
Conditions associated with bone deformity from softening includes:
bowing of long bones
biconcave vertebral bodies / codfish vertebra
There are several bony lesions that can involve or produce a sequestrum.
Brodie abscess: osteomyelitis
certain soft tissue tumors (with bony extension)
malignant fibrous histiocytoma
metastasis (especially from breast ca...
Bone mineral density (BMD) is defined as the amount of mineral (calcium hydroxyapatite) per unit of bone and can be used as an indirect indicator of bone strength.
BMD can be measured by various methods with DEXA the most prevalent:
gamma rays (gamma decay): replaced by...
Bone within a bone is a descriptive term applied to bones that appear to have another bone within them. There are numerous causes including:
thoracic and lumbar vertebrae (neonates and infants)
growth recovery lines (after infancy)
cortical splitting and new periostitis
sickle cell d...
Bowel wall thickening is a useful finding on imaging studies and has a number of different causes.
The reason for bowel wall thickening depends on the underlying etiology but includes submucosal edema, hemorrhage, and neoplastic infiltration.
In describing bow...
Breast calcifications are deposits of calcium salts in the breast, which are radio-opaque on mammography. The majority are benign, but they can be associated with cancer. The ability to diagnose and appropriately manage the significant microcalcifications and differentiate them from innocuous fi...
Breast density refers to the amount of fibroglandular tissue in a breast relative to fat. It can significantly vary between individuals and within individuals over a lifetime.
There are four descriptors for breast density on mammography in the 5th edition of BI-RADS 1,2:
Breast lumps have different characteristics that allow simplification of differential diagnosis by breaking down the vast list into sections. Consider whether the lump fits into one of these categories.
Spiculation is a feature of neoplasms and all masses that display spicula...
Bridging (or fusion) of the pubic symphysis can be associated with various systemic and local causes, including 1-3:
A bronchial stenosis is a descriptive term to denote a region of focal narrowing involving the bronchi, it can arise from a wide variety of etiologies.
It may or may not be associated in intrinsic or extrinsic mass lesion.
It can arise from a large range of etiological fac...
Bronchial wall thickening is an imaging descriptor used to describe abnormal thickening of bronchial walls and can arise from a vast number of pathological entities. It is one of the causes of peribronchial cuffing.
The presence of bronchial wall thickening usually (but not always) implies infl...
Bulging duodenal papilla is a conical or cylindrical protuberance at the medial aspect of the descending or horizontal duodenum at the site of the sphincter of Oddi. It is a finding on small bowel follow-though (and endoscopy) and has a relatively long differential. On cross-sectional imaging, ...
Calcification of the external ear (auricular cartilage) may arise from a number of causes, including:
gout and pseudogout
Calcification of the globe has many causes, varying from the benign to malignant. When calcification is seen of the posterior half of the globe, it could relate to any of the layers (scleral, choroidal or retinal), as it is not possible to separate them out on CT.
drusen: 1% population...
Calcific axillary lymphadenopathy is in general, more concerning than axillary lymphadenopathy alone and is particularly so if it contains microcalcifications. While this is concerning for malignancy, it can also occur from occasional nonmalignant causes
metastatic axillary lymp...
Calcific cervical lymphadenopathy is uncommon and has a limited differential diagnosis, including malignant and benign etiologies. The most frequent causes include 1:
malignancies (more common)
metastatic thyroid carcinoma (most common; papillary or medullary types) 2,5
There are numerous causes of calcified mediastinal lymph nodes.
Common causes include:
infectious granulomatous diseases
Uncommon causes include:
Pneumocystis jiroveci (PCP) pneumonia
thyroid carcinoma: papi...
Calcified pulmonary (lung parenchymal) densities can occur in a number of conditions.
healed varicella pneumonia 1
pulmonary alveolar microlithiasis
occupational lung diseases
coal workers pneumoconiosis
See the main article on calcified pulmon...
Calcification associated with pulmonary emboli is usually associated with chronic pulmonary embolism. Calcification is occasionally related to prior congenital cardiac repairs 1.
If it is purely high attenuating, consider
polymethylmethacrylate (PMMA) embolism into the ...
Calcified pulmonary nodules are a subset of hyperdense pulmonary nodules and a group of nodules with a relatively narrow differential.
The most common cause of nodule calcification is granuloma formation, usually in the response to healed infection.
Calcifying pulmonary metastases are rare. These should not be confused with metastatic pulmonary calcification.
Calcification in metastases can arise through a variety of mechanisms: bone formation in tumors osteoid origin, calcification and ossification of tumor cartilage, dystrophi...
Calvarial thickening can occur from a number of causes. These include:
chronic ventricular shunting 1
anemias (largely associated with massive hematopoiesis)
Cardiac calcification is a broad term for any calcification affecting the valves, coronary arteries, aortic root, endocardium, myocardium, and/or pericardium.
Causes of cardiac calcification are:
coronary artery disease (most common)
coronary artery aneurysms, e.g. in Kawasaki dise...
Cardiomegaly is a catch-all term to refer to enlargement of the heart, and should not be confused with causes of enlargement of the cardiomediastinal outline, or enlargement of the cardiac silhouette.
There are many etiologies for cardiomegaly:
congestive heart failure
The cardiophrenic space is usually filled with fat. However, lesions originating above or lower to the diaphragm can present as cardiophrenic angle lesions.
The more common lesions encountered include:
pericardial fat pad
pericardial fat necrosis
Cardiovascular (cardiac) shunts are abnormal connections between the pulmonary and systemic circulations. Most commonly they are the result of congenital heart disease.
Blood can either be shunted from the systemic circulation to pulmonary circulation (i.e. 'left-to-right shunt') or ...
Carotid pacemakers, also known as implantable carotid sinus stimulators, are devices that deliver activation energy, via carotid leads, to the carotid baroreceptors. This is sometimes offered for drug-resistant hypertension. The baroreceptors send signals to the brain and the signals are interpr...
Carpal angle is defined by two intersecting lines, one in contact with the proximal surface of the scaphoid and the lunate and the other line through the proximal margins of the triquetrum and the lunate. Its normal value is between 130° and 137°.
It is increased (>139°) in:
The differential for cartilaginous lesions includes:
There are several important causes of an abnormal lunate signal on MRI, the most frequent causes being Kienbock disease (25%), ulnar impaction syndrome (25%) and intraosseous ganglia (20%).1 Appreciation of the pattern of bone signal change can often allow the correct diagnosis to be made.
There are relatively few causes of calcification of the ascending aorta 1-3:
atherosclerosis (this usually spares the ascending aorta)
Causes of a small aorta include:
giant cell arteritis
small aorta syndrome
Cavernous sinus gas locules can be seen in several settings.
iatrogenic pneumocephalus secondary to gas embolism (especially venous gas embolism) from IV access (can be a relatively common finding in the absence of direct trauma and does not require treatment)
traumatic pneumocephalus: in the ...
A cavernous sinus mass has a wide differential including:
orbital apical inflammation with cavernous sinus involvement (Tolosa-Hunt syndrome)
any of the cranial nerves traversing the cavernous sinus: III, IV, V (V1 and V2) and VI
trigeminal schwannoma is ...
Cavitating pneumonia is a complication that can occur with severe necrotizing pneumonia and in some publications, it is used synonymously with the latter term 2. It is a rare complication in both children and adults.
Cavitation associated with Mycobacterium tuberculosis is separately discussed...
Cavitating pulmonary metastases refer to pulmonary metastases which then tend to cavitate. The term is similar but may not be identical to cystic pulmonary metastases in which the wall of the former may be thicker.
Cavitation is thought to occur in around 4% of lung metastases 2.
Distribution of bronchiectasis can help in narrowing the differential diagnosis. Central bronchiectasis is typically seen in:
allergic bronchopulmonary aspergillosis (ABPA)
congenital tracheobronchomegaly (a.k.a. Mounier Kuhn syndrome)
Williams Campbell syndrome (rare)
Centrilobular lung nodules refer to an HRCT chest imaging descriptor for small 5-10 mm lung nodules which are anatomically located centrally within secondary pulmonary lobules. The term is applied on the basis of location of the nodule and not its morphology that is they may be well defined or p...
Cerebellopontine angle (CPA) masses are relatively common. Although a diverse range of pathologies may be seen in this region, the most common by far is a vestibular schwannoma.
Cerebellopontine angle masses can be divided into four groups, based on imaging characteristics:
Cerebral atrophy is the morphological presentation of brain parenchymal volume loss that is frequently seen on cross sectional imaging. Rather than being a primary diagnosis, it is the common endpoint for range disease processes that affect the central nervous system. Though often no identifiabl...
Cerebral herniation, also referred to as acquired intracranial herniation, refers to shift of cerebral tissue from its normal location, into an adjacent space as a result of mass effect. It is a life-threatening condition that requires prompt diagnosis.
There are a number of differe...
The differential for peripheral or ring enhancing cerebral lesions includes:
demyelination (incomplete ring)
tumefactive demyelinating lesion (incomplete ring)
Vascular malformations of the central nervous system can be divided, as they can elsewhere, into high and low flow malformations.
arteriovenous malformation (AVM)
cerebral AVM (pial/parenchymal AVM)
cerebral proliferative angiopathy
dural arteriovenous fistula (DAVF)
Cervical spine injuries can involve the cervical vertebral column, intervertebral discs and cervical spine ligaments, and/or cervical spinal cord. The cervical spine accounts for ~50% of all spinal injuries.
5-10% of patients with blunt trauma have a cervical spine injury 1.
Chondrocalcinosis (plural: chondrocalcinoses) is a descriptive term indicating the presence of gross calcium deposition within articular cartilage, i.e. both hyaline and fibrocartilage.
Chondrocalcinosis articularis was an early term for calcium pyrophosphate dihydrate deposition d...
Chorioretinitis refers to inflammation of the retina and choroid. As a delayed sequelae, it is one of the causes of calcification of the globe. It is often considered a form of posterior uveitis.
various congenital infections such as 2,3
rubella: ocular rubella
Chronic bilateral airspace opacification is a subset of the differential diagnosis for airspace opacification. An exhaustive list of all possible causes of chronic bilateral airspace opacities is long, but a useful framework is as follows:
granulomatosis with polyangi...
There are several viral and prion infections which can result in a chronic encephalitis with slow progression into brain atrophy. These have a very poor prognosis with no effective treatment.
Some of these include:
progressive multifocal leukoencephalitis
subacute sclerosing panencephalitis
Chronic interstitial pneumonitis is a broad descriptive term where an interstitial pneumonia has a prolonged course. It can arise of a range of etiologies. The term does not usually imply a specific radiographic pattern and includes UIP, NSIP or other pattern. As a general rule there is little o...
Chronic primary adrenal insufficiency has a number of causes. Primary adrenal insufficiency is termed Addison disease.
idiopathic atrophy: autoimmune adrenalitis 1
tuberculosis 1: 25% calcify
fungal disease 1
Chronic suppurative lung disease (CSLD) refers to a group of conditions which includes:
primary ciliary dyskinesia
This term is usually used in the context of pediatric patients.
Chronic unilateral airspace opacification is a subset of the differential diagnoses for airspace opacification. An exhaustive list of all possible causes of chronic unilateral airspace opacities is long, but a useful framework is as follows:
Cicatrisation atelectasis is a form of lung atelectasis which occurs as a result of scarring or fibrosis that reduces lung expansion. Cicatrisation atelectasis is classic in tuberculosis. The term is closely related to cicatrisation collapse when an entire lobe is collapsed from the same process...