Carpal coalition refers to fusion of two or more carpal bones, and although the most commonly involved bones are the lunate and triquetrum, most combinations of adjacent bones can be found to be coalesced.
The estimated prevalence is ~0.1% in Caucasian Americans and ~1.5% in Afri...
The carpal tunnel is a fibro-osseous canal that acts as a passageway from the forearm to the anterior hand. It is found in the anterior wrist.
superficial border (roof): flexor retinaculum
deep border (floor): carpal bones
The carpal tunnel contains the fo...
Carrying angle is a small degree of cubitus valgus, formed between the axis of a radially deviated forearm and the axis of the humerus. It helps the arms to swing without hitting the hips while walking.
Normally it is 5-15o away from the body or 165-175o towards the body.
A decreased carrying ...
Cartilaginous joints are a type of joint where the bones are entirely joined by cartilage, either hyaline cartilage or fibrocartilage. These joints generally allow more movement than fibrous joints but less movement than synovial joints.
Primary cartilaginous joint
These cartilaginous joints...
The cauda equina is the collective term given to nerve roots distal to the conus medullaris, which occupy the lumbar cistern.
It's name comes from the Latin for "horse's tail".
Caudate nuclei are paired nuclei which along with the globus pallidus and putamen are referred to as the corpus striatum, and collectively make up the basal ganglia. The caudate nuclei have both motor and behavioral functions, in particular maintaining body and limb posture, as well as controlli...
The caudothalamic groove is an important landmark when performing neonatal cranial ultrasound.
As the name suggests, it is located between the caudate nucleus and thalamus, and is a shallow groove projecting from the floor of the lateral ventricle. It is approximately at the leve...
Many caval variants exist, due to the complex embryology of the venous system. These are important for a number of reasons:
not to confuse them with pathology
suggest the presence of frequently associated other abnormalities
planning of vascular intervention or surgery
superior vena ...
The cavernous sinuses are paired dural venous sinuses.
The cavernous sinus is located on either side of the pituitary fossa and body of the sphenoid bone between the endosteal and meningeal layers of the dura. It spans from the apex of the orbit to the apex of the petrous tempor...
The superior cavo-atrial junction, generally referred to as simply the cavo-atrial junction (CAJ), is the junction of the right lateral border of the superior vena cava (SVC) and the superior border of the right atrium.
It is an important landmark to recognize because it marks an optimum site f...
Cavum septum pellucidum (CSP) is a normal variant CSF space between the leaflets of the septum pellucidum.
While the term "cavum septum pellucidum" is generally accepted, it is grammatically incorrect. Since it denotes a space (cavum meaning cave) of the septum pellucidum, the seco...
A cavum veli interpositi (CVI), often misspelled cavum velum interpositum, is a normal variation where there is a dilated CSF space involving the velum interpositum. When larger than 1 cm in axial transverse measurement, with outwardly bowed margins and positive mass effect, the term cyst of the...
The cavum vergae (CV), along with the cavum septum pellucidum (CSP) that lies immediately anterior to it, is a persistence of the embryological fluid-filled space between the leaflets of the septum pellucidum and is a common anatomical variant.
The cavum vergae has also been refer...
The central artery of the retina or central retinal artery (CRA) arises from the ophthalmic artery.
The central artery of the retina courses anteriorly and inferior to the optic nerve, It then pierces the dura and the arachnoid of the optic nerve. It then runs in the center of t...
The central base of skull is a region of the skull base centred on the pituitary fossa and includes surrounding structures.
Despite no single universally accepted definition of this region, it is frequently used clinically and is conceptually useful particularly when considering tumors of the b...
The central canal is the longitudinal CSF-filled space which runs the entire length of the spinal cord and represents the most caudal portion of the ventricular system. It is lined by ependyma.
The central canal spans the length of the spinal cord from the caudal angle of the fou...
A number of cell groups in the reticular formation of the pons and medulla are responsible for the central control of the respiratory cycle:
inspiratory center (a.k.a. dorsal respiratory group) - bilateral groups of cells in the region of the nucleus of the tractus solitarius in the dorsum of t...
Central nervous system (CNS) embryology is complex, and below is a brief summary of its development.
The early CNS begins as a simple neural plate that folds to form a groove then tube, open initially at each end. Within the neural tube stem cells generate the two major classes of cells that m...
The central sulcus (of Rolando) is a very important landmark in both anatomical and functional neuroanatomy.
The central sulcus separates the frontal lobe from the parietal lobe, and more specifically separates the primary motor cortex anteriorly from the primary somatosensory co...
The muscle fibers of the diaphragm converge and attach to the central tendon of the diaphragm. It is a thin but strong layer of aponeurosis which forms an intergral part of respiration.
The central tendon of the diaphragm is located near the center of the diaphragmatic muscle bu...
The centrilobular region, in context of the lungs and HRCT, refers to the central portion of the secondary pulmonary lobule, around the central pulmonary artery and bronchiole.
The centrum semiovale is a mass of white matter superior to the lateral ventricles and corpus callosum, present in each of the cerebral hemispheres, subjacent to the cerebral cortex.
It has a semi-oval shape and contains projection, commissural, and association fibers. Inferolaterally these fib...
The cephalic vein, along with the basilic vein, is one of the primary superficial veins that drain the upper limb 1. It courses through both the forearm and arm and terminates by draining into the axillary vein.
origin: radial aspect of the superficial venous network of the dorsum of...
Cerebellar agenesis is a rare congenital abnormality which can result from failure to develop normal cerebellar tissue or destruction of normally developed tissue.
For a more general overview of cerebellar malformations, please refer to the article on classification systems for malformations of...
The cerebellar nuclei comprise 4 paired deep grey matter nuclei deep within the cerebellum near the fourth ventricle. They are arranged in the following order, from lateral to medial:
dentate nuclei (the largest and most lateral)
fastigial nuclei (most medi...
The cerebellar tonsils are ovoid structures on the inferiormedial surface of each cerebellar hemisphere. They are attached to the underlying cerebellum by the tonsillar peduncle 1-4.
medial: uvula of the vermis
superior: flocculonodular lobe
anterior: posterior surfa...
The cerebellopontine angle cistern is a triangular CSF-filled subarachnoid space that lies between the anterior surface of the cerebellum and the lateral surface of the pons.
superior: tentorium cerebelli
posterior: anterior surface of cerebellum
inferior: lower cra...
The cerebral aqueduct (of Sylvius) is the structure within the brainstem that connects the third ventricle to the fourth. It is located within the midbrain, surrounded by periaqueductal grey matter (PAG) with the tectum of midbrain located posteriorly and the tegmentum anteriorly.
It is filled ...
The two cerebral hemispheres are divided in the midsagittal plane by the interhemispheric fissure. Together they fill most the intra-cranial cavity.
The medial surface of each cerebral hemisphere is flat, the inferior surface is irregular and even slightly concave anteriorly, whi...
The cerebral meninges surround the brain and is made up of three layers (from outermost to innermost):
The dura mater can also be known as pachymeninx. The arachnoid mater and pia mater are collectively known as the leptomeninges 3. The spinal meninges ar...
The cerebral peduncles (also known as the cerebral crus) are the part of the midbrain that link the remainder of the brainstem to the thalami and thereby, the cerebrum. They are the most anterior structure in the midbrain and contain the large ascending and descending tracts that run to and from...
Cerebral sulci and fissures are grooves between the adjacent gyri on the surface of the cerebral hemispheres. By allowing the cortex to invaginate to form sulci and gyri the surface area of the cortex is is increased threefold 4. The result is that the surface area of the human cortex is 2200 cm...
An understanding of cerebral vascular territories is important in understanding stroke and complications from surgery and endovascular procedures.
Although one could be excused for thinking that within the brain, such a carefully organised organ, blood supply would be constant, the truth is th...
The cerebral veins drain the brain parenchyma and are located in the subarachnoid space. They pierce the meninges and drain further into the cranial venous sinuses.
The cerebral veins lack muscular tissue and valves. The cerebral venous system can be divided into:
superficial (cortical) cerebr...
The cerebral venous system, somewhat unlike the majority of the rest of the body, does not even remotely follow the cerebral arterial system.
The cortical veins lie superficially, unlike cortical arteries, and are adherent to the deep surface of the arachnoid mater so that they keep the sulci o...
Cerebrospinal fluid (CSF) is the clear liquid that surrounds and bathes the brain and spinal cord.
CSF is produced by the epithelium of the choroid plexus within the ventricular system and flows in the direction from the lateral ventricles to the third ventricle, then fourth ventricle and then ...
The cerebrum is a paired neural structure composed of the two cerebral hemispheres (left and right) each containing a central space, the lateral ventricle. It develops from the telencephalon.
The cerebrum takes up most of the intracranial cavity and lies above the tentorium cereb...
Cervical aortic arches are a rare aortic arch anomaly characterized by an elongated, high-lying aortic arch extending at or above the level of the medial ends of the clavicles.
Patients with cervical aortic arch are usually asymptomatic. Symptomatic patients may present w...
The cervical enlargement of the spinal cord is the source of the spinal nerves that contribute to the brachial plexus and supply the upper limbs.
It is one of two symmetrical enlargements which occupy the segments of the limb plexuses, the other being the lumbosacral enlargement ...
Sequential morphological ultrasound changes of the endocervical canal with cervical incompetence can be remembered using the mnemonic:
Trust Your Vaginal Ultrasound
T-shaped (normal internal cervical os)
The cervical ligament attaches to the calcaneus and talus. It is lateral to the tarsal sinus and medial to the attachment of extensor digitorum brevis. It is taut in inversion.
Cervical lymph node groups describe the anatomic position of the nodes. It differs from cervical lymph node levels, covering all lymph nodes not just those relevant to head and neck surgery.
Groups described in the literature include but are not limited to:
The cervical plexus is formed by the ventral (anterior) rami of the C1 to C5 nerve roots and innervates the diaphragm, provides motor supply to some neck muscles and cutaneous sensation to the skin of the head, neck and chest.
anterior rami of C1 to C5 nerves
Cervical plicae palmatae are normal folds seen on the anterior and posterior walls of the cervical canal. They are often described as longitudinal ridges or oblique elevation.
Sometimes they are identified on MRI, and one must make sure not to misinterpret this finding as abnormal. Studies repo...
Cervical ribs are supernumerary or accessory ribs arising from the seventh cervical vertebra. They occur in ~0.5% of the population, are usually bilateral, but often asymmetric 2, and are more common in females.
Although cervical ribs are usually asymptomatic, they are the most important anato...
The cervical spine is the upper part of the spine extending from the skull base to the thorax at the level of the first vertebra with a rib attached to it. It normally consists of seven vertebrae. Its main function is to support the skull and maintain the relative positions of the brain and spin...
Cervical spine ligaments ordered from anterior to posterior include:
anterior longitudinal ligament (ALL)
anterior atlanto-occipital membrane
alar ligaments (paired)
cruciate ligament of the atlas
longitudinal band: joins the body of the axis to the foramen magnum
The cervix or uterine cervix is the lower constricted segment of the uterus providing the passage between the uterus proper and the vagina.
The cervix is somewhat conical in shape, with its truncated apex directed posteriorly and inferiorly. The inferior aspect of the cervix pro...
Chassaignac bursa (also known as the retromammary bursa, submammary serous bursa or occasionally Chassaignac bag) is the space behind the breast, lying between the pectoralis fascia posteriorly and deep layer of superficial fascia anteriorly.
It contains loose connective tissue and aids in mobi...
Chest x-ray lines and stripes are important to recognize on chest radiographs.
Lines are usually less than 1 mm in width and are comprised of tissue outlined on either side by air and typically represent pleural-covered structures within the middle and superior mediastinum 1,2:
The chordae tendineae are thin strong inelastic fibrous chords that extend from the free edge of the cusps of the atrioventricular valves (the tricuspid and mitral valves) to the apices of the papillary muscles within the right and left ventricles respectively. They transmit the force of the co...
The chorda tympani is a nerve that arises from the mastoid segment of the facial nerve, carrying afferent special sensation from the anterior two-thirds of the tongue via the lingual nerve, as well as efferent parasympathetic secretomotor innervation to the submandibular and sublingual glands.
The chorion is one of the embryonic membranous structures than encloses both the fetus as well as the amnion. The chorion begins to form chorionic villi towards its outer surface, which initially serves to provide nutrition to the developing embryo.
Part of the chorionic villi arborize more ex...
The chorionic plate is a synonym for the fetal side of the placenta. The maternal side of the placenta is termed the basal plate.
Some pathologies and processes are localized to the chorionic plate, and evaluation of the chorionic plate is a part of placental grading.
Choroidal epithelial cells are one of the three types of ependymal cells, themselves a type of glial cell. They cover the surface of the choroid plexus and produce cerebrospinal fluid (CSF). 1.
The choroidal fissure, or choroid fissure, is a cleft of the medial surface of the brain that forms the medial wall of the lateral ventricle and attachment site for the choroid plexus.
The C-shaped fissure runs between the fornix (body, crus, and fimbria) and the thalamus. At the...
The choroid plexus is located within the cerebral ventricles and is made of epithelial cells, loose connective tissue (tela choroidea) and permeable capillaries. It produces cerebrospinal fluid.
roof of the temporal horns of the lateral ventricles, extending along the ...
Chromaffin cells are neuroendocrine cells found predominantly in the medulla of the adrenal gland. They are also found in other ganglia of the sympathetic nervous system and are derived from the embryonic neural crest.
They arise in the fifth week of fetal development when neuroblas...
The ciliary ganglion is one of four parasympathetic ganglia of the head and neck. It receives parasympathetic fibers from the oculomotor nerve.
smallest of the ganglia (2mm in size)
located posterolaterally in the intraconal space of the orbit (towards the orbital apex) between ...
The cingulate gyrus lies on the medial aspect of the cerebral hemisphere. It forms a major part of the limbic system which has functions in emotion and behavior. The frontal portion is termed the anterior cingulate gyrus (or cortex) 1,2.
The cingulate gyrus extends fro...
The cingulate sulcus is situated directly superior to the cingulate gyrus, which is formed by the medial surface of the frontal lobes that is directly above the corpus callosum.
The Circle of Willis is an arterial polygon formed as the internal carotid and vertebral systems anastomose around the optic chiasm and infundibulum of the pituitary stalk in the suprasellar cistern. This communicating pathway allows equalization of blood-flow between the two sides of the brain,...
Circumaortic left renal vein, also known as circumaortic renal collar is an anomaly of left renal vein when a supernumerary or accessory left renal vein passes posterior to the aorta, apart from the normal renal vein passing anterior to the aorta. This anomaly is potentially hazardous, if unreco...
Circumcaval ureter, also known as retrocaval ureter, is a term used to describe an abnormal course of a ureter that encircles the inferior vena cava. Both of these terms are somewhat misleading, as this configuration is considered a developmental anomaly of the inferior vena cava (IVC). There ar...
The circumflex artery (Cx) is a major coronary artery that divides off the left main coronary artery (the other branch being the left anterior descending (LAD) artery).
The circumflex artery is referred to by multiple terms:
circumflex artery (Cx)
ramus circumflex artery (RCx)
The circumflex fibular artery is a minor artery of the leg.
Origin and course
Most often arises from the posterior tibial artery, passes laterally round the neck of the fibula through the soleus to anastomose with the lateral inferior genicular, medial genicular and anterior tib...
The circumventricular organs are neuroendocrine anatomical structures localised around the ventricles of the brain. They are characterized by a rich vasculature and fenestrated (permeable) capillaries. As such, with the exception of the subcomissural organ, they are also characterized by the abs...
The cisterna chyli (CC), also known as the receptaculum chyli, is a normal anatomical structure seen as a saccular area of dilatation in the lymphatic channels that is located in the retrocrural space, usually to the immediate right of the abdominal aorta 4.
The cisterna magna (also known as the cerebellomedullary cistern) is the largest of the CSF-filled subarachnoid cisterns.
The cisterna magna is located between the cerebellum and the dorsal surface of the medulla oblongata at and above the level of the foramen magnum. CSF produce...
The claustrum is a vertical curved sheet of subcortical grey matter oriented sagittally between the white matter tracts of the external capsule and extreme capsule. It is lateral to the putamen and medial to the insular cortex. It is not part of the basal ganglia.
There are lateral and medial t...
The clavicle, also known as the collar bone, is the only bone connecting the pectoral girdle to the axial skeleton and is the only long bone that lies horizontally in human skeleton.
The clavicle is roughly "S-shaped" with a flattened, concave, lateral one-third and a...
The clavipectoral fascia is a sheet of loose connective tissue which is the deep layer of fascia in the pectoral region. It acts to suspend the floor of the axilla.
The clavipectoral fascia lies below the clavicular head of the pectoralis major. It fills in the space between the...
Cleft epiphysis is a normal variant of an epiphysis. It can be either unilateral or bilateral. The most common site is the epiphysis of the first proximal phalanx of the foot.
Plain radiographs will demonstrate a lucent defect in the epiphysis. The borde...
The clivus is the sloping midline surface of the skull base anterior to the foramen magnum and posterior to the dorsum sellae 1. Specifically, it is formed by the sphenoid body and the basiocciput, which join at the spheno-occipital synchondrosis. At the clivus, the occipital bone has articulati...
The cloaca is the terminal portion of the hindgut. It is an embryonic structure (weeks 4-7) in which the distal ends of the gastrointestinal tract and urogenital system share a common channel. The most distal aspect of the cloaca is termed the cloacal membrane.
The cloaca, or portions of it, ca...
Cloquet's canal, also known as the hyaloid canal or Stilling's canal, is a transparent canal that runs from the optic nerve disk to the lens traversing the vitreous body. It serves as a perivascular sheath surrounding the hyaloid artery in the embryonic eye.
History and etymology
The coccygeus, also known as the ischiococcygeus, is a remnant muscle of the pelvic floor.
The coccygeus is a paired muscle which is triangular in shape and overlies the sacrospinous ligament. The coccygeus lies parallel to the inferior border of the piriformis, but is separated ...
The coccyx (plural: coccyges) is the series of rudimentary vertebrae forming the caudal termination of the vertebral column and is positioned inferior to the apex of the sacrum. The coccyx is one leg of the tripod formed in conjunction with the ischial tuberosities for support in a seated positi...
The cochlea is part of the inner ear osseous labyrinth found in the petrous temporal bone.
The cochlea is a shell-shaped spiral that turns between two-and-a-half and two-and-three-quarters times around the modiolus (a central column of porous bone).
The spiral of the cochlea is...
The cochlear duct (also known as the scala media) is housed centrally in the cochlea which is part of the inner ear along with the vestibular apparatus 1,4. The cochlea is located in the bony labyrinth, which is found in the temporal bone 2.
The cochlear duct is a cavity filled w...
Thin osseous septum separating the semicanal for tensor tympani and the bony Eustachian tube.
The cochlear promontory is the name given to the bone that overlies the basal turn of the cochlea protruding into the middle ear cavity.
glomus tympanicum paragangliomas typically arise in the region of the cochlear promonotory
Celiac artery, also known as the celiac axis or celiac trunk, is a major visceral artery in the abdominal cavity supplying the foregut. It arises from the abdominal aorta and commonly gives rise to three branches: left gastric artery, splenic artery, and common hepatic artery.
The coeliacomesenteric trunk represents an uncommon vascular anatomical variant where both the celiac trunk and the superior mesenteric artery have a common origin from the abdominal aorta as a single trunk. Its frequency has been reported to occur in about 1.5% of the population 1,2.
The collateral ligaments of the foot are attached to the dorsal tubercles on the metatarsal heads and the corresponding side of the phalangeal bases.
The collateral sulcus, also known as the medial occipitotemporal sulcus, runs anteroposteriorly on the inferior surface of the temporal lobe and occipital lobe. Anteriorly it is sometimes continuous with the rhinal sulcus 1-3.
Anteriorly, it separates the fusiform gyrus laterally, from the par...
There are several collateral systems between the primary vascular supply of the foregut and midgut.
The collateral between the celiac trunk and superior mesenteric artery include:
gastroduodenal artery (GDA)
branch of the common hepatic artery and anastomoses with branches of the inferior pa...
The colliscalene triangle is an important anatomical region of the neck, situated medial to the scalenus anterior muscle.
medial: lateral border of longus colli
lateral: medial border of scalenus anterior
inferior: first part of the subclavian artery
apex: carotid ...
The columella is the most anteroinferior portion of the nasal septum and forms the central fleshy portion between the two nostrils when looking at someone's nose. It is a single midline structure composed of cartilage and overlying skin, extending posteriorly from the tip of the nose. The latera...
There are a number of white matter tracts that cross the midline, connecting the two cerebral hemispheres. These are known as commissures and include:
hippocampal commissure (psalterium)
The common bile duct (CBD), which is sometimes simply known as the bile duct, is formed by the union of the cystic duct and common hepatic duct.
The CBD is approximately 8 cm long and usually <6 mm wide in diameter but this can be dependent on a number of factors including age a...
The common carotid artery is a paired structure that supplies blood to the head and neck.
left: branch of the aortic arch
right: branch of the brachiocephalic trunk
course: posterior to sternoclavicular joint, lateral to thyroid and trachea
supply: head and neck
The common facial vein is formed by the joining of the facial vein and anterior branch of the retromandibular vein. It is part of the venous drainage system of the face.
origin and termination: the facial vein (along with the facial artery) pierces the deep investing fascia of the neck...