Maxillodental leave alone lesions are usually incidental findings that do not require treatment nor follow-up if the patient is asymptomatic.
This article includes findings from orthopantomogram, cone-beam CT, and sinus CT studies.
Do not touch:
Leave alone lesions are findings that are usually discovered incidentally and do not require any specific treatment or follow-up if the patient is asymptomatic.
This article includes findings from paranasal sinus CT and MRI studies.
Skeletal leave alone lesions, also called “do not touch” lesions, are so characteristic radiographically, that further diagnostic tests such as a biopsy are unnecessary and can be frankly misleading and lead to additional unnecessary surgery. Thus a radiologic diagnosis should be made without a ...
Leave alone lesions of the skull base refers to incidental findings that do not require treatment nor follow-up.
This article includes findings from brain CT, HRCT of the temporal bone, and MRI studies.
Do not touch:
arrested pneumatization of the skull base - sphenoid benign fatty lesion 1
When a central venous catheter that is supposed to terminate in the superior vena cava or right atrium is abnormally located to the left of the mediastinum and below the level of the brachiocephalic vein, a limited differential of left paramediastinal catheter position should be considered 1:
Leg bowing in children is common and often developmental.
The differential includes:
exaggeration of normal age-related angulation changes at the knee
neonates and infants normally have varus angulation that gradually corrects within 6 months of w...
Leptomeningeal enhancement refers to a diffuse or focal gyriform or serpentine enhancement that can be seen in the following conditions:
tuberculous meningitis (can also be focal)
CNS cryptococcal infection
coccidioidal meningitis (c...
Lesions of the corpus callosum are uncommon and arise from multiple different etiologies. The lesions can be classified according to underlying pathophysiology 4-6.
agenesis of the corpus callosum
enlarged perivascular spaces
tubonodular pericallosal lipoma: associated with dysgen...
Linear atelectasis (plural: atelectases), and also known as discoid or plate atelectasis refers to a focal area of subsegmental atelectasis that has a linear shape. Linear atelectasis may appear to be horizontal, oblique or perpendicular and is very common. It usually occurs as a consequence of ...
Linitis plastica is a descriptive term usually referring to the appearance of the stomach, although the rectum can also be described this way. The appearance is said to be reminiscent of an old leather water-bottle.
The underlying cause is usually a scirrhous adenocarcinoma with diff...
Lobar consolidation is the term used to describe consolidation in one of the lobes of the lung. It infers an alveolar spread of disease and is most commonly due to pneumonia.
Consolidation refers to the alveolar airspaces being filled with fluid (exudate/transudate/blood), cells (inf...
Lobar collapse refers to the collapse of an entire lobe of the lung. As such it is a subtype of atelectasis (collapse is not entirely synonymous with atelectasis, which is a more generic term for 'incomplete expansion'). Individual lobes of the lung may collapse due to obstruction of the supply...
Localized pulmonary hemorrhage is a descriptive term for a pulmonary hemorrhage restricted to a particular focal region of the lung. It can range from involving a small focus of hemorrhage to a whole lobe.
Focal pulmonary hemorrhage can occur from a number of causes:
Long bone metaphyseal cupping is most likely due to the local oligemia from thrombosis in the terminal epiphyseal arteries to the epiphyseal plate, induced by prolonged regional immobilization 7.
The differential diagnosis of long bone metaphyseal cupping includes:
Longitudinally extensive spinal cord lesions (LESCL), also known as longitudinally extensive transverse myelitis (LETM), represent extensive involvement of the spinal cord, with abnormal T2 signal traversing at least three vertebral body segments in length.
They are typi...
Loss of intervertebral disc space can be due to a variety of causes:
degenerative disc disease of the spine: most common cause
dialysis related spondyloarthropathy
crystal deposition diseases
Causes of calcifications in the lower abdomen and pelvis include:
seminal vesicle and ductus deferens calcification
dropped stones ...
Lower gastrointestinal bleeding usually occurs distal to the ligament of Treitz, and has a wide differential diagnosis:
There are relatively few causes of low signal intensity renal parenchyma. Causes include:
paroxysmal nocturnal hemoglobinuria
mechanical: malfunctioning prosthetic cardiac valve
sickle cell disease
hemorrhagic fever with renal syndrome (HFRS)
Lytic bone metastases are due to a variety of primary tumors, and are more common than sclerotic metastases (although many may occasionally have mixed lytic and sclerotic components). They include 1:
renal cell cancer
adrenocortical carcinoma and pheochromocytoma
Lytic skull lesions have a relatively wide differential that can be narrowed, by considering if there are more than one lesion and whether the mandible is involved.
lytic skeletal metastases
epidermoid - scalloped border with a sclerotic rim
The increased globe size or macrophthalmia may have many differentials:
buphthalmos (congenital glaucoma)
macrophthalmus in neurofibromatosis type 1 (NF1)
connective tissue disorders: Marfan syndrome, Ehlers-Danlos syndrome
Here is a list of some of the most useful differential diagnoses in musculoskeletal imaging.
lucent/lytic bone lesions (FEGNOMASHIC)
multiple lucent/lytic bone lesions
benign lytic bone lesions in patients under 30 years old
diffuse bony sclerosis
permeative process in bone
Malignant neoplasms involving the uterus account for a significant proportion of all female cancers.
They can be classified as:
endometrial carcinoma : commonest: >90% of all uterine malignancies
endometrioid carcinoma of the uterus: commonest histological type, ~80%
papillary serous carcino...
Malignant esophageal neoplasms are much more common than benign esophageal neoplasms, especially if the patient is symptomatic.
esophageal carcinoma (90%)
esophageal squamous cell carcinoma (SCC)
esophageal spindle cell carcinoma
Barium meal has been frequently used to differentiate malignant and benign gastric ulcers:
Features suggesting benign gastric ulcer
outpouching of ulcer crater beyond the gastric contour (exoluminal)
smooth rounded and deep ulcer crater
smooth ulcer mound
smooth gastric folds that reach the...
Mandibular lesions are myriad and common. The presence of teeth results in lesions that are specific to the mandible (and maxilla) and a useful classification that defines them as odontogenic or non-odontogenic. While it may often not be possible to make a diagnosis on imaging alone, this classi...
There are many causes for mandibular periostitis:
Langerhans cell histiocytosis
malignancy (both primary and metastatic)
necrosis, e.g. radiation osteonecrosis
Garre's sclerosing osteomyelitis
The differential diagnosis of masses arising from the foramen of Monro can be approached depending on the age of the patient.
choroid plexus papilloma
Langerhans cell histiocytosis
subependymal giant ce...
Mass-forming chronic pancreatitis occurs in around 30% of cases of chronic pancreatitis, where a mass or a focal enlargement of the pancreas is usually seen on imaging. In many instances, it poses a challenge as the epidemiology and imaging appearances overlap those of pancreatic adenocarcinoma....
Mastoid air cell opacification can occur in a number of situations and can include a spectrum of inflammatory, neoplastic, vascular, fibro-osseous, and traumatic changes.
Possible causes include:
trauma (temporal bone f...
Maurice "Mo" M Reeder (1933-2013) was an American radiologist who is remembered for his contributions to radiology education in the United States, in particular, the development of the radiology-pathology teaching program at the Armed Forces Institute of Pathology.
Maurice Merrick R...
Meckel cave lesions are numerous. The aim of this article is to list them in an easy way for revision and assessment of differential diagnosis.
Meckel cave tumors account for only 0.5% of all intracranial tumors. The most common histologies are:
trigeminal schwannoma: most common,...
Mediastinal lymph node enlargement can occur from a wide range of pathologies, either by its own or in association with other lung pathology. Historically, a size cut-off of 10 mm short-axis diameter was used.
Although mediastinal lymphadenopathy is used interchangeably - by some ...
The differential diagnoses for mediastinal widening include:
traumatic aortic injury
thoracic aortic aneurysm
aberrant right subclavian artery
azygos continuation of the IVC
pulmonary masses abutting the m...
Medical devices in the abdomen and pelvis are important to be recognized, just like medical devices of the chest. Often we ignore these devices, considering them to be incidental and non-pathological, however it is essential to be aware of potential complications.
Medical devices in the head and neck are regularly observed by radiologists on plain film, CT and MRI reporting. They include devices which pass through the neck into the chest and stomach or ascend to/into the head.
Vascular access devices
peripherally inserted central cat...
Medical devices in the thorax are regularly observed by radiologists when reviewing radiographs and CTs.
tubing, clamps, syringes, scissors, lying on or under the patient
rubber sheets, foam mattresses, clothing, hair braids, nipple piercings, etc. may also be visible
Renal medullary nephrocalcinosis is the commonest form of nephrocalcinosis and refers to the deposition of calcium salts in the medulla of the kidney. Due to the concentrating effects of the loops of Henle, and the biochemical milieu of the medulla, compared to the cortex, it is 20 times more co...
Megaesophagus or diffuse esophageal dilatation can be caused by a variety of conditions.
Some of the more common causes are given below 1-3:
malignant stricture, e.g. esophageal cancer, ca...
Meningeal enhancement is a generic term related to the enhancement of the membranes that envelop the brain and spinal cord. Due the anatomical features, this enhancement can be divided in two subtypes:
leptomeningeal enhancement (pial or pial-arachnoid enhancement)
dural (pachymeningeal) enhan...
Metal-on-metal pseudotumors represent mass-forming inflammation around a metal-on-metal hip or knee replacement. The term describes one presentation on the spectrum of adverse reaction to metal debris.
Metal-on-metal pseudotumors are large focal solid or semiliquid masses...
The metaphyseal blanch sign (or metaphyseal blanch sign of Steel) is one of the signs seen on AP views of the adolescent hip indicating posterior displacement of the capital epiphysis.
It is a crescent-shaped area of increased density, that overlies the metaphysis adjacent to the physis on the ...
The differential diagnosis for metaphyseal lesions includes:
aneurysmal bone cyst
simple bone cyst
giant cell tumor
There are a range of middle ear tumors, which are more likely to be benign than malignant.
The three most common middle ear tumors are (not in any particular order as there are differences in the literature) 1-3:
glomus tympanicum paraganglioma
The differential diagnosis for a middle mediastinal mass includes 1-3:
aneurysm e.g. aortic, pulmonary artery, bronchial artery
foregut duplication cyst (e.g. esophageal, bronchial)
primary/secondary cardiac tumor
Midline neck masses have a relatively narrow differential, as few structures are present in the midline. Dividing the causes according to structure of origin is a useful schema.
lymph node(s): Delphian node(s)
thyroglossal duct cyst
One of the most important indicators of increased intracranial pressure due to mass effect is midline shift.
Any intra-axial or extra-axial lesion (tumor, hemorrhage, abscess, etc.) has the potential to exert mass effect on the brain parenchyma and cause lateral shift of the midline ...
The term miliary opacities refers to innumerable, small 1-4 mm pulmonary nodules scattered throughout the lungs. It is useful to divide these patients into those who are febrile and those who are not.
Additionally, some miliary opacities are very dense, narrowing the differential - see multiple...
Milk of calcium within a breast cyst is a mammographic feature observed when there is dependent calcium layering within breast cysts. It is typically observed as "tea cup" or "crescent shaped" calcifications on a true lateral (LM or ML) view on occasionally on a MLO view. On a CC view, these cal...
A mixed cystic and solid pituitary region mass has a limited differential.
both papillary (more solid) and adamantinomatous (more cystic)
cystic change / necrosis / previous hemorrhage
Most other solid and enhancing pituitary region mas...
Mixed lytic and sclerotic bone metastases are seen in a number of malignancies:
breast carcinoma: typically sclerotic but 25% are mixed
lung carcinoma: typically lytic but 15% are mixed
carcinoma of the cervix
prostate carcinoma: typically sclerotic but 15% are mixed
Monoarthritidies have a relatively short differential diagnosis, including:
Charcot joint (neuropathic joint)
pigmented villonodular synovitis (PVNS)
Monoarticular arthropathy can result from a number of causes:
septic arthritis (8-27%)
rheumatoid arthritis (RA) (11-16%)
Less common 2:
HADD (hydroxyapatite deposition disease)
reactive arthritis 2
Mosaic attenuation is a descriptive term used in describing a patchwork of regions of differing pulmonary attenuation on CT imaging. It is a non-specific finding, although is associated with the following:
obstructive small airways disease: low attenuation regions are abnormal and reflect two p...
Mostly/purely cystic pituitary region masses have a short differential.
Rathke cleft cyst
craniopharyngioma (adamantinomatous type): 90% have calcification
Moyamoya syndrome, also termed the moyamoya pattern or phenomenon, is due to numerous conditions that can cause arterial occlusion of the circle of Willis, with resultant collaterals, and appearances reminiscent of moyamoya disease. These conditions include 1-4 :
vessel wall abnormalities
Mucoid impaction, also referred to as mucus plugging, mucous plugging, bronchial mucocele or bronchocele formation, refers to airway filling by mucoid secretions and can be obstructive or non-obstructive. It is a common pathological finding in chest imaging.
A multicentric breast cancer is a term given to a breast cancer where there are two or more breast cancers separated by normal breast tissue (often taken as 5 cm of separation 4). It is related to but distinct from the term multifocal breast cancer.
At a pathological level It can also mean 2
Multifocal breast cancer refers to two or more individual breast cancers diagnosed at the same time within the same quadrant of the same breast 1.
Multilayered periosteal reaction, also known as a lamellated or onion skin periosteal reaction, demonstrates multiple concentric parallel layers of new bone adjacent to the cortex, reminiscent of the layers on an onion. The layers are thought to be the result of periods of variable growth 2 and ...
The most common causes of multiple cranial nerve thickening and enhancement include:
metastasis (most common)
neurofibromatosis type II
lymphoma and leukemia
chronic inflammatory demyelinating polyneuropathy
cranial nerve enhancement: for comple...
The differential diagnosis for multiple cystic neck lesions is different to that for a solitary cystic neck mass.
Cystic neck lesions are seen in:
metastatic squamous cell carcinoma: older patient, M>F
metastatic papillary thyroid carcinoma: usually a younger patient, ...
Multiple filling defects within a ureter, as seen on conventional IVU or CT IVU, have a relatively small differential including:
spreading or multifocal transitional cell carcinoma (TCC)
multiple ureteral stones (steinstrasse)
Intracranial calcifications are common in certain locations and often are of no clinical concern.
The two most commonly encountered types of calcification include:
normal age-related intracranial calcifications
intracranial arterial atherosclerosis
Concerning calcifications are much less co...
Myocardial edema refers to an increased water content of the myocardium particularly within the extracellular interstitium 1.
Myocardial edema often reflects an acute or subacute cardiac event, most often either ischemic or inflammatory and thus can be associated with che...
Myonecrosis is a myopathy involving infarction of skeletal muscle and can have the appearances of an intramuscular mass.
Myonecrosis represents an infarction of the skeletal muscles. It has a variety of causes 1,2,3:
post-traumatic (see: calcific myonecrosis) - most common
A narrow fetal thorax on antenatal ultrasound can be present with a number of anomalies which include:
Jeune syndrome - asphyxiating thoracic dysplasia
short rib polydactyly syndro...
The interpedicular distance is the measurement between the pedicles on frontal/coronal imaging, which can be narrowed in a number of situations.
thanatophoric dysplasia 2
widening of interpedicular distance
See reference 1 for an old but interesti...
Causes of neonatal distress can be broadly split into intrathoracic, extrathoracic and systemic:
respiratory distress syndrome (RDS)
transient tachypnea of the newborn (TTN)
meconium aspiration syndrome
bronchopulmonary dysplasia (BPD)
patent ductus arteriosus (PDA)
The differential diagnosis for masses of the cauda equina region is often considered separately to the remainder of the spinal cord. It is often difficult to determine whether masses in this region are intramedullary or intradural-extramedullary.
Most common tumors
Nephrocalcinosis, previous known as Anderson-Carr kidney or Albright calcinosis, refers to the deposition of calcium salts in the parenchyma of the kidney. It is divided into several types, with differing etiologies, based on the distribution:
medullary nephrocalcinosis: 95%
Nerve root enhancement is phenomenon described on post contrast MRI scans that can be observed in a number of situations.
post-operative nerve root enhancement
disseminated spinal leptomeningeal metastases
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-cardiogenic pulmonary edema is a classification of pulmonary edema where the underlying etiology is not due to left ventricular dysfunction. Causes include:
pulmonary edema with acute asthma
post-obstructive pulmonary edema/postintubation pulmonary edema/negative pressure ...
Non-neoplastic solid lesions of the pancreas are conditions which may mimic pancreatic neoplasms on imaging. They include:
intrapancreatic accessory spleen
peripancreatic lymph node
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 of the urinary tract. Depending on the severity of obstruction and extent, it may result in permanent change in both the collecting system ...
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 ...
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...
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...
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...
Optic canal enlargement can be caused by numerous etiologies.
The optic canal has an average transverse diameter of 3.6 ± 0.6 mm 1. The optic canal can be considered enlarged when it is >6.5 mm in transverse diameter 4.
glioma of optic nerve
meningioma of optic nerve shea...
Enlargement of the optic nerves is uncommon and has a surprisingly broad differential.
optic nerve glioma
optic nerve meningioma
involvement by retinoblastoma
cyst of optic nerve sheat...
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 ...
An orbital mass carries a relatively wide differential:
lacrimal gland or duct tumors
rhabdomyosarcoma of the orbit
optic nerve meningioma
optic nerve glioma
schwannoma (of trigeminal or other cranial nerves except optic)
Orbital vascular lesions may be difficult to distinguish on imaging. However, the following conditions have been described:
arteriovenous malformation (AVM)
orbital lymphangioma / lymphangiovenous malformation / venolymphatic malformation
The differential for osteoporosis includes:
mastocytosis (mast cells produce heparin)
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: