N-acetylaspartate (NAA) is one of the more important compounds assessed on MR spectroscopy, and resonates at 2.0 ppm chemical shift.
NAA is the acetylated form of the amino acid, aspartate, which is found in high concentrations in neurons and is a marker of neuronal viability. It is therefore ...
N-acetylcysteine (NAC) if often used as a prophylaxis against contrast induced nephropathy. Protocols for administration vary widely from institution to institution and the true efficacy is still controvertial.
A typical protocol is [1-2]:
600 mg acetylcysteine twice daily on the day of the e...
Nabothian cysts (also known as a retention cysts of the cervix 11) are non-neoplastic cystic lesion that occurs in relation to the uterine cervix.
They are common and some reports suggest that they may seen in up to 12% of routine pelvic MRI scans 2.
The Naclerio V sign is a sign described on the plain film in patients with a pneumomediastinum occurring often secondary to an oesophageal rupture.
It is seen as a V-shaped air collection. One limb of the V is produced by mediastinal air outlining the left lower lateral mediastinal border. The...
The Naegele's formula is simple arithmetic method for calculating the EDD (estimated date of delivery) based on the LMP (last menstrual period).
To the date of the first day of the LMP (e.g. 22nd June 2008):
add seven days (i.e 29th)
subtract 3 months (i.e March)
The Nager syndrome (also known as acrofacial dysostosis) is a rare congenital syndrome primarily characterised by facial and skeletal features
There may be agenetic defect localized to chromosome 9q32. Most cases are thought to be sporadic . Occasional autosomal recessive a...
Nail-patella syndrome, also known as Fong disease, is a rare autosomal dominant condition which results from a symmetrical meso and ectodermal abnormalities.
Clinically the key feature is absent/hypoplastic nails from birth. Individuals may have flexion contractures and r...
The naked facet sign (also known as the hamburger sign or reverse hamburger bun sign) refers to the CT appearance of an uncovered vertebral articular facet when the facet joint is dislocated, most often in cases of locked facet.
This CT sign is characteristic of a flexion-distraction injury an...
Named fractures are usually eponymous or occupational. The simplest way of spiting them up is by body area:
upper extremity fractures
lower extremity fractures
Using names on Radiopaedia.org is common when describing procedures and the history surrounding eponymous names.
When referring to a person, do not use punctuation in the name and use spaces between initials. For example:
Dr R F Player (correct)
Dr. R. F. Player (incorrect)
Dr RF Player (inc...
The napkin-ring sign (cardiac) is a recently described sign encountered on CT-coronary angiogram (coronary CTA) performed on modern MDCT (number of rows 64 or higher). It has been shown to possess a high predictive value in predicting future cardiac events and is considered one of the imaging co...
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 (IP) distance which is the distance measured between the pedicles on frontal / coronal imaging can be narrowed in a number of situations
thanatophoric dysplasia 2
widening of interpedicular distance
See reference 1 for an old b...
The nasal bones are paired oblong upper central facial bones placed side by side between the frontal processes of the maxilla, jointly forming the nasal ridge.
The nasal bones has two surfaces:
external surface attaches the procerus and nasalis muscles
internal, which is transv...
Nasal bone fractures are the most common type of facial fractures, accounting for ~45% of facial fractures, and are often missed when significant facial swelling is present.
Unsurprisingly, nasal bone fractures occur when the nose impacts against a solid object (e.g. fis...
The nasal cavity forms part of the aerodigestive tract.
The nasal cavity is formed by 1:
anteriorly: nasal aperture
laterally: inferior, middle and superior nasal conchae or turbinates
superiorly: cribiform plate of the ethmoid bone
inferiorly: palatal processes of the maxill...
The nasal conchae are long, narrow curled shelves of bone that protrude into the nasal cavity. The superior, middle and inferior conchae divide the nasal cavity into three groove-like air passages.
The conchae are located laterally in the nasal cavity and covered by pseudostratified columnar, c...
Nasal encephalocoeles are the herniation of cranial content in the nasal area. It is one of the causes of craniospinal dysraphism.
Nasal encephaloceles usually present at birth with symptom of obstruction or other complications. It presents as an external swelling on the ...
Nasal gliomas, also know as nasal glial heterotopia, are a rare congenital lesion composed of dysplastic glial cells which have lost their intracranial connections and present as an extranasal or intranasal mass.
Nasal gliomas are rare congenital lesions. These masses occur spora...
Nasal septal perforation may affect either the bony, or cartilaginous septum. Most commonly it affects the anterior septal cartilaginous area although with syphilis it characteristically affects the bony septum.
Symptoms include a nasal discharge, nasal congestion (loss o...
A not-very-useful mnemonic for the causes of nasal septum perforation is:
Say Water Coke Syrup Sugarwater Lemonade or Say Nothing
W: Wegener granulomatosis
N: non-Hodgkin T-cell lymphoma (NHL)
The nasion is the midline bony depression between eyes where the frontal and two nasal bones meet, just below the glabella. It is also known as the bridge of the nose.
It is one of the skull landmarks, craniometric points for radiological or anthropological skull measurement.
Naso-orbitoethmoid (NOE) fractures (also known as orbitoethmoid or nasoethmoidal complex fractures) are fractures which involve the central upper midface.
Naso-orbitoethmoid (NOE) fractures are caused by a high-impact force applied anteriorly to the nose and transmitted posteriorly t...
Assessment of nasogastric (NG) tube positioning is a key competency of all doctors as unidentified malpositioning may have dire consequences, including death.
The ideal position should be in the sub-diaphragmatic position in the stomach - identified on a plain chest radiograph as overlying the ...
Nasolabial cyst (also known as nasoalveolar cyst or Klestadt`s cyst) is a rare non-odontogenic, soft-tissue, developmental cyst occurring inferior to the nasal alar region. The cyst is derived from epithelial cells retained in the mesenchyme after fusion of the medial and lateral nasal processes...
The nasolacrimal (drainage) apparatus consists of:
Tears produced by the lacrimal gland, accessory lacrimal glands of Krause Wolfring and Zeis, and Meibomian glands track medially along the eyelid margins and collect at the lacrimal lake at ...
The nasolacrimal duct is the terminal part of the nasolacrimal apparatus.
Then nasolacrimal duct is the inferior continuation of the lacrimal sac and is ~17 mm in length in total. There are two parts to the nasolacrimal duct:
intraosseous part (12 mm): lies within nasolacrimal c...
Nasolacrimal duct mucocele represents cystic dilatation of the nasolacrimal apparatus secondary to proximal +/- distal obstruction of the nasolacrimal duct.
Presentation is common early in infancy, typically 4 days to 10 weeks. Infants present with small round bluish medi...
This suture forms the fissure between the frontal process of maxilla and the lateral border of the nasal bone. The nasomaxillary sutures are paried.
The nasopalatine nerve (also known as the long sphenopalatine nerve) is a branch of the pterygopalatine ganglion.
exits the pterygopalatine ganglion in the pterygopalatine fossa
passes through the sphenopalatine foramen to enter the nasal cavity
passes along the roof of...
Nasopharyngeal carcinomas (NPC) are the most common primary malignancy of the nasopharynx. It is of squamous cell origin and some types of which are strongly associated with Epstein Barr virus (EBV).
Nasopharyngeal carcinomas account for approximately 70% of all primary malignanci...
Nasopharyngeal carcinoma is staged using the TNM staging system with derived stage groupings.
Primary tumour (T)
Tx: primary tumour cannot be assessed
T0: no evidence of primary tumour
Tis: carcinoma in situ
T1: tumour is confined to the nasopharynx
T2: tumour extends to soft...
A nasopharyngeal choristoma is a rare, non-neoplastic mass (type of choristoma) typically located in the lateral aspect of the nasopharynx without intracranial extension. These lesions are composed of fibrovascular tissue and fat. Resection is curative.
A mnemonic for causes of nasopharyngeal masses is:
S: squamous cell carcinoma
A: antrachoanal polyp
I: inverted papilloma
L: lethal midline granuloma
The nasopharynx forms part the pharynx, being the continuation of the nasal cavity superiorly, and the oropharynx inferiorly.
anteriorly: posterior nares and posterior margin of nasal septum 1,2
inferiorly: soft palate 2
superiorly: basi-sphenoid and basi-occiput 1...
The National Institutes of Health Stroke Scale (NIHSS) is a score calculated from 11 components and is used to quantify the severity of strokes. The 11 components are:
level of consciousness (1a: 0-3, 1b: 0-2 and 1c: 0-2)
best gaze (0-2)
visual fields (0-3)
facial palsy (0-3)
arm motor (0-...
The navicular bone is found in the midfoot and is one of the tarsal bones. It's structure resembles that of a boat. It is the last bone of the foot to ossify fully 1.
location: lies within the medial aspect of the midfoot
relations: the talus bone, cuboid bone and the three cuneiform ...
Near drowning pulmonary oedema is considered an aetiological sub type of non cardiogenic pulmonary oedema. It can occur with both salt or fresh water drowning.
It is thought to result from the inhalation of either fresh or sea water resulting in lung damage and ventilation-perfusion...
There are several types of neck dissections which can classified as follows:
Radical neck dissection
Radical neck dissection is considered to be the standard basic procedure for cervical lymphadenectomy. All other procedures represent one or more alterations of this procedure. The dissection i...
Neck tongue syndrome (NTS) is rare and comprises altered sensation in one side of the tongue aggravated by neck movement, with ipsilateral neck pain 1.
NTS is seen in a wide range of ages but is more commonly reported in older children and young adults 1-3.
Necrobiotic pulmonary nodules are sterile cavitating lung nodules associated with inflammatory bowel disease (more often with ulcerative colitis than with Crohn's disease) and rheumatoid arthritis.
Histologically, necrobiotic nodules consist of a core of fibrinoid necrosis and steri...
Necrotising enterocolitis (NEC) is the most common gastrointestinal condition in premature neonates, and continues to have significant mortality and morbidity.
NEC usually develops 2-3 days following birth, with 90% developing within the first 10 days of life 4. The incidence is i...
Necrotising enterocolitis (NEC) can be staged into three groups, helping to guide appropriate treatment. In general stage I and II are managed medically, whereas stage III is managed surgically.
lethargy, temperature instability, apnoea, bradycardia
emesis, abdominal d...
Necrotising fasciitis refers to a rapidly progressive and often fatal infection of soft-tissue fascia deep to the skin but superficial to the muscles.
Necrotising fasciitis is relatively rare, although its prevalence is thought to be rising due an increase in the number of immunoc...
Necrotising otitis externa (NOE), also known as malignant otitis externa, is a severe invasive infection of the external auditory canal (EAC) which can spread rapidly to involve the surrounding soft tissue, adjacent neck spaces and skull base.
Predisposing conditions for NOE include...
Necrotising pancreatitis (NP) represents the severe form of pancreatitis. It is generally considered a subtype of acute pancreatitis as necrosis usually tends to occurs early, (within the first 24-48 hours) but can also rarely occur with subacute forms.
A key feature is a significant amount of ...
Necrotising pneumonia (NP) refers to a pneumonia characterised by the development of the necrosis within infected lung tissue. While the term has sometimes been used synonymously with a cavitating pneumonia in some publications 2, not all necrotising pulmonary infections may be complicated by ca...
Necrotising sarcoid granulomatosis (NSG) is a rare systemic disease, characterised by sarcoid-like granuloma formation, vasculitis and variable degrees of necrosis. It is sometimes classified under the group of pulmonary angiitis and granulomatois.
It typically affects affecting m...
The negative enhancement integral in MR perfusion is used to calculate the relative cerebral blood volume (rCBV). It represents the area described by the baseline and the signal loss due to passage of contrast bolus in tissue.
Negative predictive value of a test/investigation is defined as the proportion of patients with negative results being truly disease free.
Negative predictive value = true negatives detected / total negative results
(where "total negative results" = true negative + false...
Negative ulnar variance describes a state where the ulna is abnormally shortened compared to the radius and plays an important role in wrist pathology.
There is a significant association between negative ulnar variance and Kienböck disease, although the majority of people with negative ulnar va...
This classification was proposed by Neimeier and later modified by Anderson et al in 1987, which at the time of writing (July 2016) remains the most widely accepted classification for gall bladder perforation.
According to this classification, there are three main clinical sub types.. A fourth...
Neonatal appendicitis is rare, presumably in part due to the short funnel shape to the appendix at that age. Symptoms are non-specific and may mimic necrotising enterocolitis.
Neonatal bilious vomiting has a relatively narrow differential - those conditions that cause intestinal obstruction, but do so distal to the ampulla of Vater. As such, the list includes:
malrotation with midgut volvulus
The neonatal chest radiograph in the exam setting may strike fear into the heart of many radiology registrars, but it need not!
There are only a limited number of diagnoses that will be presented on such films and they are often highlighted by the history.
First of all, have a look ...
Neonatal encephalopathy is a clinical syndrome referring to signs and symptoms of abnormal neurological function in the first few days of life in a neonate born at or beyond 35 weeks of gestation. It is described as difficulty with initiating and maintaining respiration, depression of tone and r...
Neonatal herpes simplex encephalitis is caused by vertical transmission of infection during passage from birth canal with diffuse cerebral involvement within the first month after birth; in contrast to adult herpes simplex encephalitis, it is commonly related to HSV-2.
Neonatal hydronephrosis is most commonly diagnosed antenatally as fetal pylectasis.
pelvi-ureteric junction (PUJ) obstruction (50% of cases 1,6)
vesicoureteric reflux (~20% of cases 5)
posterior urethral valves (~10 6)
vesico-ureteric junction (VUJ) obstruction
Neonatal hypoxic-ischaemic encephalopathy (HIE) is the result of a global hypoxic-ischaemic brain injury in a term neonate, usually after asphyxia.
It is important to remember that neonatal encephalopathy may result from a variety of conditions and hypoxic-ischaemic brain injury is...
Neonatal lines and tubes are widely used in the NICU (neonatal intensive care unit) in the management of critically ill neonates. Examples include:
central venous line
umbilical artery catheter
umbilical vein catheter
The NG tube serves ...
Neonatal pneumonia refers to inflammatory changes of the respiratory system caused by neonatal infection.
It is one of the leading causes of significant morbidity and mortality in developing countries. Neonatal pneumonia accounts for 10% of global child mortality. At the time of w...
The causes of neonatal pneumoperitoneum are different from adult pneumoperitoneum and include:
perforated hollow viscus
necrotising enterocolitis (NEC): most common
meconium ileus in cystic fibrosis
intestinal atresia or web
peptic ulcer disease
Neonatal pneumothorax describes pneumothoraces occurring in neonates. It is a life threatening condition, associated with high morbidity and mortality. The diagnosis is a challenge especially when the amount of air is small and may accumulate along the anterior or medial pleural space.
Causes of neonatal distress can be broadly split into intrathoracic, extrathoracic and systemic:
respiratory distress syndrome (RDS)
transient tachypnoea of the newborn (TTN)
meconium aspiration syndrome
bronchopulmonary dysplasia (BPD)
patent ductus arteriosus (PDA...
Type I: Absent or minimal femoral head changes.
A: deformity of the femoral head with intact physis.
B: deformity of the femoral head with premature physeal closure.
Type III: Pseudarthrosis of the femoral neck.
A:Complete destruction of the capital femoral epiphysis wit...
There are number of neoplasms that can involve the appendix, some of which are peculiar to this site.
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 tumours
Neoplasms of the spinal canal encompass a range of tumours which arise from or involve the spinal cord, theca and nerves. These can be divided according to the tissue/structure of origin. Tumours of vertebral bodies are discussed separately: see vertebral body tumours.
Spinal cord (intramedull...
Neostriatum is the name given to the caudate nucleus and the putamen (the putamen is the outer layer of the lentiform nucleus).
The term is sometimes abbreviated to striatum, however, this should be distinguished from corpus striatum (which is the caudate nucleus in addition to the...
Nephroblastomatosis refers to diffuse or multifocal involvement of the kidneys with nephrogenic rests (persistent metanephric blastema).
Nephrogenic rest are found incidentally in 1% of infants.
Nephrogenic rests are foci of metanephric blastema that persist beyond 36 ...
Nephrocalcinosis refers to the deposition of calcium salts in the parenchyma of the kidney. It is divided into several types, with differing aetiologies, based on the distribution:
medullary nephrocalcinosis: 95%
cortical nephrocalcinosis: 5%
partial, combined cortical and medullary nephrocal...
Nephrogenic systemic fibrosis (NSF), also known as nephrogenic fibrosing dermopathy, is a complication of gadolinium based contrast agents used in imaging studies.
It is characterised by "firm, erythematous, and indurated plaques of the skin associated with subcutaneous oedema" 1. Eve...
Nephroptosis, also known as floating or wandering kidney and ren mobilis, refers to the descent of the kidney more than 5cm or two vertebral bodies when the patient moves from a supine to upright position during IVU 1-2.
Displacement can also occur medially across the midline, so-called medial ...
Nephrostomy is a common urologic or interventional radiology procedure in which a tube/catheter is introduced into the renal collecting system (usually the renal pelvis).
Nephrostomies can either be
"open" nephrostomy: after a urological surgical procedure, such as a UPJ stone remova...
Nephrotic syndrome (NS) results from loss of plasma proteins in the urine and characterised by hypoalbuminemia, hyperalbuminuria, hyperlipidemia, and oedema. It may be caused by primary (idiopathic) renal disease or by a variety of secondary causes.
Patients present with ...
The nerve to obturator internus and superior gemellus is formed from the anterior (ventral) divisions of the L5, S1 and S2 nerve roots of the sacral plexus. The nerve supplies the obturator internus and superior gemellus muscles as well as the fascia of the lateral side wall of the ischioanal fo...
Nerve to the piriformis muscle also known as piriformis nerve arises from the S1 and S2 nerve roots of the sacral plexus. The nerve supplies the piriformis muscle.
The nerve to the piriformis muscle arises from the sacral plexus. The nerve branches from the posterior div...
The nerve to quadratus femoris and inferior gemellus is formed from the anterior (ventral) divisions of the L4, L5 and S1 nerve roots of the sacral plexus. The nerve supplies the quadratus femoris and inferior gemellus muscles as well as providing an articular branch to the hip joint.
The nerve to stapedius arises from the facial nerve to supply the stapedius muscle. The facial nerve branch is given off in its mastoid segment, as it passes posterior to the pyramidal process.
Damage to this branch with resulting paralysis of stapedius leads to hypersensitivity to loud noises ...
The nervus intermedius, also known as nerve of Wrisberg, is a part of cranial nerve VII (facial nerve) which contains somatic sensory, special sensory, and visceral motor (secretomotor) fibres 1.
superior salivary nucleus
parasympathetic supply to the lacrimal and major ...
The nervus terminalis, also referred to as cranial nerve zero, cranial nerve XIII, zero nerve, nerve N or NT, is a previously unnumbered cranial nerve, most rostral of all cranial nerves.
It is a bilateral bundle of nerve fibres, which runs in the subarachnoid space from the medi...
The net magnetisation vector (NMV) in MRI is the summation of all the magnetic moments of the individual hydrogen nuclei.
In the absence of an external magnetic field, the individual magnetic moments are randomly oriented and since they are in opposition, the NMV is considered to be zero.
Neu-Laxova syndrome (NLS) is a lethal, autosomal recessive multiple malformation syndrome with a heterogeneous phenotype.
The clinical spectrum can be quite wide and includes
dermal / cutaneous
severe skin restriction
decreased fetal movement
Neuhauser sign refers to a soap bubble appearance seen in the distal ileum in cases of meconium ileus, related to the air mixed with meconium. It may be seen with barium enema if contrast passes beyond the ileocaecal valve or with small-bowel follow-through.
Although classically described with ...
Neural tube defect (NTD) refers to incomplete closure of the neural tube in very early pregnancy.
The neural tube comprises of a bundle of nerve sheath which closes to form brain at the anterior end and spinal cord at posterior end. The closure should occur at around the 28th day of conception...
Neurenteric cysts are a rare type of foregut duplication cyst, accounting for ~1% of all spinal cord tumours. They are usually classified as spinal or intracranial, and are associated with vertebral or CNS abnormalities respectively.
Neurenteric cysts result from incomplete resorpti...
Neuritic plaques (also known as senile plaques) are a feature of Alzheimer's disease. They are extracellular and composed of a central core of beta-amyloid peptides aggregated together with fibrils of beta-amyloid, dystrophic neurites, reactive astrocytes, phagocytic cells, and other proteins an...
Neuroanatomy encompasses the anatomy of all structures of the central nervous system, which includes the brain and the spinal cord.
Neuroaxonal leukodystrophy is a rare adult-onset white matter disease. The disease is now encompassed within adult onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP).
History and examination
The clinical presentation is of progressive cognitive and motor dy...
Neuroblastic tumours arise from primitive cells of the sympathetic system and include the following entities:
These entities represent a spectrum of disease from undifferentiated and aggressive (neuroblastoma) to the well differentiated and l...
Neuroblastomas are tumours of neuroblastic origin corresponding to the most common extracranial solid childhood malignancies and the third commonest childhood tumours after leukaemia and brain malignancies. It accounts for ~15% of childhood cancer deaths.
The tumours typically occ...
There are two methods of neuroblastoma staging, one that is based on post-operative patients (INSS) and one developed for pre-treatment patients (INRGSS).
International Neuroblastoma Staging System (INSS)
This staging system is for post-operative patients and mainly for prognosis 1:
Both neuroblastoma and Wilms tumour occur in early childhood and typically present as large abdominal masses closely related to the kidneys. Distinguishing between the two is important, and a number of features are helpful.
calcification very common: 90%
encases vascular structu...