Articles

Articles are a collaborative effort to provide a single canonical page on all topics relevant to the practice of radiology. As such, articles are written and edited by countless contributing members over a period of time. A global group of dedicated editors oversee accuracy, consulting with expert advisers, and constantly reviewing additions.

45 results found
Article

I-131

I-131​ (or 131I) is a radioisotope used in the diagnosis and treatment of thyroid lesions. It is one of the oldest radiotracers used in nuclear medicine, in use for over 50 years. It is predominately used in thyroid ablation therapy, for patients post thyroidectomy, and for metastatic thyroid ca...
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Ice-cream cone sign

The ice cream cone sign may refer to: the appearance of the head of malleus and the body and short process of the incus on axial CT scan: failure of this normal configuration suggests incudomalleolar dysarticulation the ball of the ice cream is formed by the head of malleus and cone is formed ...
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Incisive canal

The maxillary incisive canal runs through the maxilla in the midline. It connects the inferior nasal cavity with the superior oral cavity, opening at the incisive foramen posterior to the central maxillary incisor teeth. It contains the descending palatine artery and the nasopalatine nerve.  Re...
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Incisive canal cyst

Incisive canal cysts, also known as nasopalatine duct cysts (NPDC), are developmental, non-neoplastic cysts arising from degeneration of nasopalatine ducts. These ducts usually regress in fetal life. The persistence of ductal epithelium leads to formation of cyst. It is considered the most comm...
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Incisive foramen

The incisive foramen (also known as nasopalatine foramen or anterior palatine foramen) is the oral opening of the nasopalatine canal. It is located in the maxilla in the incisive fossa, midline in the palate posterior to the central incisors, at the junction of the medial palatine and incisive s...
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Incisive nerve

The incisive nerve is one of the two terminal branches of the inferior alveolar nerve, a branch of the posterior division of the mandibular division of the trigeminal nerve. It continues running anteriorly in the medullary cavity of the mandible after the mental nerve branches off and exits via ...
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Incus

The incus is the middle of the ossicles articulating with the head of the malleus anteromedially and the stapes inferomedially. Its parts include: a body which articulates with the head of the malleus, and to which the superior ligament of the incus is attached (to the roof of the middle ear c...
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Infantile cervical ligament oedema

Infantile cervical ligament oedema can typically be seen when infants have suffered accidental or abusive head and neck trauma. The finding is best seen on sagittal STIR images. Terminology The posterior ligamentous complex refers to the ligamentum flavum and interspinous ligaments. The anteri...
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Inferior alveolar artery

The inferior alveolar artery is a branch of the maxillary artery. It runs with the inferior alveolar nerve as it descends through the infratemporal fossa and enters the mandibular canal and supplies mandibular teeth. In the region of the first premolar it bifurcates into the incisive and mental ...
Article

Inferior alveolar nerve

The inferior alveolar nerve or inferior dental nerve is a mixed sensory and motor branch of the posterior division of the mandibular division of the trigeminal nerve in the pterogomandibular space of the oral cavity. Gross anatomy The inferior alveolar nerve divides off the posterior division ...
Article

Inferior longitudinal muscle of the tongue

The inferior longitudinal muscle of the tongue is one of the 4 intrinsic muscles of the tongue which alters the shape of the tongue mass, being entirely confined to the tongue without an attachment outside the tongue (like the extrinsic muscles of the tongue). Gross anatomy The muscles fibres ...
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Inferior median clival canal

The inferior median clival canal also known as the canalis basilaris medianus is a rare anatomical variant of the clivus, which passes in the sagittal plane from the intracranial surface of the clivus to its retropharyngeal surface. It is generally thought to represent a remnant of the notocord....
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Inferior nasal concha

The inferior nasal concha is one of the conchae in the nose. It extends horizontally along the lateral wall of the nasal cavity and consists of a lamina of spongy bone, curled upon itself like a scroll. Each inferior nasal concha is considered a facial pair of bones since they arise from the max...
Article

Inferior oblique muscle

The inferior oblique muscle is one of six extra-ocular muscles that control eye movements. Summary origin: orbital surface of the maxilla insertion: globe (posterior, inferolateral surface) innervation: inferior branch of the oculomotor nerve (CN III) primary function: one of two ocular ext...
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Inferior ophthalmic vein

The inferior ophthalmic vein (IOV) is a vein of the inferior orbit and is smaller than the more well known superior ophthalmic vein. Gross anatomy The vein forms at the confluence of several veins within the anteroinferior orbit along the infraorbital margin from facial vein tributaries. It co...
Article

Inferior pharyngeal constrictor muscle

The inferior pharyngeal constrictor muscle is one of the pharyngeal constrictor muscles. Its primary action is constriction of the pharynx (in coordination with the superior pharyngeal constrictor and the middle pharyngeal constrictor muscles) to deliver a bolus of food into the oesophagus. Sum...
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Inferior rectus muscle

The inferior rectus muscles is one of the 6 extra-ocular muscles that control eye movements. Summary innervation: inferior branch of the oculomotor nerve (CN III) origin: Annulus of Zinn (tendinous ring) insertion: globe (anterior, inferior surface) primary function: one of two ocular depre...
Article

Inferior thyroid artery

The inferior thyroid artery is a branch of the thyrocervical trunk (85%) or subclavian artery (15%) and ascends to enter the thyroid gland on its posterior surface, as well as supplying both the superior and inferior parathyroid glands 1. The nerve is closely related to the ascending limb of the...
Article

Infrahyoid muscles

The infrahyoid muscles or strap muscles are a group of four paired muscles in the anterior neck below the hyoid bone, within the muscular triangle. They are responsible for depressing the hyoid during swallowing. The four muscles are: sternohyoid: superficial and medial omohyoid: superficial ...
Article

Infraorbital artery

The infraorbital artery is a branch of the third part of the maxillary artery. It runs through the inferior orbital fissure, orbit, infraorbital canal then the infraorbital foramen. Here it gives off the anterior superior alveolar artery which supplies the anterior teeth and the anterior part of...
Article

Infraorbital foramen

The infraorbital foramen is located in the maxillary bone. It is the anterior opening of the infraorbital canal, which is the anterior continuation of the infraorbital groove, which course through the floor of the orbit. The canal may reside entirely in the maxillary sinus, suspended from the si...
Article

Infraorbital nerve

The infraorbital nerve is a branch of the maxillary division of the trigeminal nerve.   Gross anatomy The infra-orbital nerve divides off the maxillary division just after emerging from the foramen rotundum to enter the pterygopalatine fossa. It courses laterally over the palatine bone and max...
Article

Infratemporal fossa

The infratemporal fossa is a complex space that lies posterolateral to the maxillary sinus and many important nerves and vessels traverse it.  Gross anatomy The infratemporal fossa is the space between the skull base, lateral pharyngeal wall and the ramus of mandible.  Boundaries medially - ...
Article

Infratrochlear nerve

The infratrochlear nerve is an extraconal branch of the nasociliary nerve, a branch of ophthalmic division of the trigeminal nerve. Some authors describe it as the terminal branch of the nasociliary nerve. It courses through the medial aspect of the extraconal space of the orbit inferior to the ...
Article

Ingested bones

Ingested bones that become lodged in the throat or gastro-intestinal tract are a common presentation to the emergency department. Recognition is important because these cases can be potentially fatal.  Pathology Patients may present with a 'foreign body' feeling in the throat after eating fish...
Article

Inion

The inion is the tip of external occipital protuberance, the midline bony prominance in the occipital bone where the ligamentum nuchae and trapezius muscle attaches. It is usually easily palpable. It is the the surface marking of the internal attachment of the tentorium cerebelli. It is one of...
Article

Inner ear

The inner ear refers to the bony labyrinth and its contents and the membranous labyrinth. It is divided into three sections: cochlea vestibule semicircular canals
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Innervation of the muscles of the middle ear (mnemonic)

A useful mnemonic to remember innervation of the muscles of the middle ear is: S for Stapedius T for Tensor Tympani Mnemonic S: Stapedius is supplied by a branch of the facial nerve- the Seventh cranial nerve. It is also the Smallest muscle in the body, and inserts onto the neck of Stapes T...
Article

Inspissated colloid

Inspissated colloid (colloid crystals) in a thyroid nodule leads to focal hyperechogenic foci, which can potentially be confused with microcalcifications. Radiographic features hyperechoic focus in a thyroid nodule reverberation artifact / comet-tail artifact this feature is the most reliabl...
Article

Internal acoustic canal

The internal acoustic canal (IAC), also known as the internal auditory canal or meatus (IAM), is a bony canal within the petrous portion of the temporal bone that transmits nerves and vessels from within the posterior cranial fossa to the auditory and vestibular apparatus. Gross anatomy The op...
Article

Internal auditory canal nerves (mnemonic)

A mnemonic to remember the relative position of nerves inside the internal auditory canal (IAC) is: Seven up, Coke down Anatomy Four nerves pass through the IAC: facial nerve (CN VII) three components of the vestibulocochlear nerve (CN VIII) cochlear nerve (CN VIIIc) superior vestibular n...
Article

Internal carotid artery

The internal carotid artery is a terminal branch of the common carotid artery.  Gross anatomy Origin It arises most frequently between C3 and C5 vertebral level, where the common carotid bifurcates to form the internal carotid and the external carotid artery (ECA). Variations in origin Alt...
Article

Internal jugular vein

The internal jugular vein (IJV) is the major venous return from the brain, upper face and neck. Gross anatomy Origin and course It is formed by the union of inferior petrosal and sigmoid dural venous sinuses in or just distal to the jugular foramen (forming the jugular bulb). It descends in t...
Article

Internal jugular vein tributaries (mnemonic)

A useful mnemonic to remember the branches of the internal jugular vein is: Medical Schools Let Fun People In Mnemonic From inferior to superior: M: middle thyroid vein S: superior thyroid vein L: lingual vein F: facial vein P: pharyngeal vein I: inferior petrosal sinus
Article

Internasal suture

The internasal suture is a single, midline cranial suture between the two nasal bones. It meets the frontonasal suture to form the nasion 1.
Article

Intraconal orbital compartment

The intraconal orbital compartment or intraconal space is the conical space within the orbit, the base of which is anterior and is formed by the posterior half of the globe. The sides are formed by the extraocular muscles and their surrounding fascia which pass posteriorly and converge on the te...
Article

Intraconal orbital lesions

Intraconal orbital lesions are broadly divided to two main groups; those with or without involvement of the optic nerves: Lesions with optic nerve involvement: optic nerve glioma optic nerve meningioma optic neuritis pseudotumour lymphoma and leukaemia intracranial hypertension retinobla...
Article

Intracranial dermoid cyst

Intracranial dermoid cysts are uncommon lesions with characteristic imaging appearances. They can be thought of as along the spectrum: from epidermoid cysts at one end (containing only desquamated squamous epithelium) and teratomas at the other (containing essentially any kind of tissue from all...
Article

Intraductal papiloma of salivary gland

Intraductal papilloma of salivary gland (also known as an inverted ductal papilloma or sialadenoma papilliferum) is a benign relatively rare salivary gland tumour. ' Epidemiology They typically arise in adulthood and there may be a slight male predilection. Pathology They may show a characte...
Article

Intraosseous meningioma

Intraosseous meningioma, also referred as primary intraosseous meningioma, is a rare subtype of meningioma that accounts for less than 1% of all osseous tumours. They fall under the subgroup of primary extradural meningiomas. Terminology It is important to note that it has been argued by some ...
Article

Intrinsic muscles of the larynx

The intrinsic muscles of the larynx can be considered in two groups: muscles that control the inlet of the larynx muscles that move the vocal ligaments Gross anatomy Muscles of the inlet aryepiglottic muscle: lies within the aryepiglottic fold, runs from the side of the epiglottis and inser...
Article

Intrinsic muscles of the tongue

The intrinsic muscles of the tongue are a group of 4 muscular bands in the tongue. In comparison to the extrinsic muscles of the tongue, they are entirely within the tongue with no external attachments. They act to alter the shape of the tongue where as the extrinsic tongue muscles alter the pos...
Article

Inverted papilloma

Inverted papillomas are a type of Schneiderian papilloma. They are uncommon with distinctive pathological and imaging features. Terminology  The term inverted papilloma is also used to describe a urothelial lesion. For a discussion of that entity, please refer to inverted papilloma of the urin...
Article

Iodine-123

Iodine123 (I123) is a radioisotope of the element Iodine (atomic number 53) used in nuclear medicine imaging including to image the thyroid gland.  Uses, dosages, and time of Imaging routine scan: 100-400 microCi po, image at 4-6 or 24 hours thyroid cancer scan: 1.5 mCi po, image at 4-6 or 24...
Article

Isolated cleft palate

An isolated cleft palate is a type of facial cleft. This is a much rarer occurrence than a cleft lip +/- palate and is thought to represent a different pathological entity. Epidemiology The estimated incidence is at ~1 per 2000-2500 pregnancies 4-5. There may be a slight female predilection 4....

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