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.

29 results found

Raccoon sign

Raccoon sign is periorbital ecchymosis and is indicative of skull base fracture of anterior cranial fossa.

Radiation-associated lens opacities

Radiation-associated lens opacities, also known as radiation induced cataracts, address changes in the lens of the eye by radiation. Pathogenesis The lens of the eye is one of the most radiosensitive tissues in the body. Exposure to ionizing radiation can cause cataract formation which can dev...

Radiographic assessment of basilar invagination

Five lines have been described and used by most of the radiologists to evaluate basilar invagination on frontal and lateral skull plain film as well as coronal and mid-saggital recontructed CT images. This is based on relative projection of odontoid process to these lines, which is as follows ...

Radiolucent lesions of the mandible

Lucent lesions of the mandible are not uncommon and may be the result of odontogenic or non-odontogenic processes. Lucency may be conferred by a cystic process (e.g. periapical cyst) or a lytic process (e.g. mandibular metastases). Pathology Aetiology Odontogenic periapical (radicular) cyst ...

Raindrop skull

The appearance of multiple, well-defined lytic lesions (punched out lesions) of various size scattered throughout the skull constitutes the raindrop skull appearance of multiple myeloma. This term is applied as an analogy to rain hitting a surface and splashing, where it leaves a random pattern ...

Ranawats line

Ranawats line is the perpendicular distance between centre of the sclerotic ring of C2 and a line drawn along the axis of C1 vertebra Normal value is 17mm in males and 15mm in females. It is deceased in basilar invagination .


Ranulas are a rare benign acquired cystic lesions that occur at the floor of mouth as submandibular or minor salivary glands retention cysts.  Epidemiology For reasons that are unclear, they appear to be more common in the Maori of New Zealand and Pacific Island Polynesians 7. Clinical presen...

Rathke's cleft cyst

Rathke's cleft cysts, also known as pars intermedia cysts, are nonneoplastic, sellar or suprasellar epithelium-lined cysts arising from the embryologic remnants of Rathke's pouch in the pituitary gland. They are common lesions and usually incidentally identified.  Epidemiology Rathke cleft cys...

Reactive vs malignant lymph nodes - ultrasound features

A number of sonographic features are helpful in distinguishing reactive versus malignant lymph nodes. Grey scale features Features that favour reactive / infective nodes over malignancy include: nodal matting 
 surrounding soft tissue oedema 
 Doppler features Doppler examination ...

Recreational drug use: radiological manisfestations

Radiological manifestations of recreational drug use are not infrequently seen as the use of recreational drugs is widespread. Epidemiology Interestingly, recent reports have suggested a decreasing incidence of reported drug use in the general population over the past decade, but it remains th...

Recurrent laryngeal nerve

The recurrent laryngeal nerve (RLN), also know as the inferior laryngeal nerve, is a branch of the vagus nerve (CN X) which has a characteristic loop around the right subclavian artery on the right and the aortic arch on the left before returning up to achieve the tracheoesophageal groove and th...

Residual cyst of the mandible

A residual cyst is a basket term referring to any residual cystic space post surgery. It is most frequently seen as a remnant of a periapical cyst.

Retinal detachment

Retinal detachment is a detachment of the retina proper from the underlying pigmented choroid, and occurs in some settings: tractional: inflammatory or post-traumatic fibrous bands in the vitreous; also seen in sickle cell disease exudative: fluid accumulating in the subretinal space secondary...


Retinoblastoma (Rb) is the most common intraocular neoplasm found in childhood, and with modern treatment modalities is, in most cases, curable. Epidemiology Retinoblastoma may be sporadic or secondary to a germline mutation of the RB tumour suppressor gene which is usually inherited. It may b...

Retrodiscal zone

The retrodiscal (bilaminar) zone is located between the posterior band of the TMJ disc and the posterior portion of the TMJ capsule. The 'bilaminar' refers to the two posterior attachments of the disc: superior layer: elastic to allow anterior translation of the disc over the articular eminence...

Retrodural space of Okada

The retrodural space of Okada is a wishbone-shaped potential space which links the facet joints to each other at a single level across the midline, and thus acts as a potential pathway for the spread of injected material (contrast, air, steroid, local anaesthetic) as well as infection.  Gross a...

Retrolental fibroplasia

Retrolental fibroplasia (also known as retinopathy of prematurity) is an ocular condition seen in the infant population. It often occurs bilaterally although usually with significant asymmetry 1.  Epidemiology There is often a history of premature delivery, low birth weight, and/or prolonged v...

Retromandibular vein

The retromandibular vein runs through the substance of the parotid gland. It lies deep to the facial nerve and superficial to the external carotid artery. The retromandibular vein is formed, usually within the parotid, by the confluence of the maxillary vein and the superficial temporal vein. B...

Retromolar trigone

The retromolar trigone is an oral cavity subsite that is consists of the mucosa posterior to the last mandibular molar. It is roughly triangular shaped and extends superiorly towards the maxilla along the anterior surface of the mandible.  Related pathology squamous cell carcinoma

Retropharyngeal abscess

Retropharyngeal abscess is a potentially life-threatening infection involving the retropharyngeal space which requires prompt diagnosis and aggressive therapy. Epidemiology Retropharyngeal abscesses are most frequently encountered in children, with 75% of cases occurring before the age of 5 ye...

Retropharyngeal space

The retropharyngeal space (also known as the true retropharyngeal space to distinguish it from the danger space, which is sometimes referred to as part of the retropharyngeal space) is one of the seven deep compartments of the head and neck. It is a midline space that consists largely of fatty a...

Rhabdomyosarcoma of the orbit

Rhabdomyosarcomas of the orbit account for approximately 10-20% of all rhabdomyosarcomas and are usually found in children.  Epidemiology As with other locations, rhabdomyosarcomas in the orbit are over represented in males, and in Caucasians. They typically occur in children below the age of ...

Rhinocerebral mucormycosis

Rhinocerebral mucormycosis (RM) refers to an uncommon form of invasive fungal sinus infection. Clinical presentation The presentation can vary ranging from exophthalmos, rhinorrhoea, and ophthalmoplegia with some patients rarely having loss of visual acuity and peripheral facial palsies 4. Pa...


A rhinolith (also known as nasal calculus) is an uncommon lesion that results from complete or partial mineralised encrustation of intranasal foreign bodies as a result of a chronic longstanding inflammatory response.  Clinical presentation Most rhinoliths ultimately produce clinical symptoms ...


Rhinoscleroma is a chronic granulomatous infection involving the upper respiratory tract due to Klebsiella rhinoscleromatis. It initially involves the nasal mucosae but it may progress to any other part of the upper respiratory tract. Untreated rhinoscleroma slowly progresses over many years 1....

Riedel thyroiditis

Riedel thyroiditis is a very rare form autoimmune thyroiditis. It is sometimes considered as a manifestation of a wider systemic disease with fibrosis of the retroperitoneum, mediastinum, as well as lymphocytic infiltration of extraocular orbital muscles, salivary and lacrimal glands 4. Most rec...

Robin sequence

Robin sequence (also called Pierre Robin syndrome or Pierre Robin anamaloid) is a congenital condition characterized by facial abnormalities. Its aetiology has no genetic base, but rather, is reliant on a sequence of events, one following the other. Terminology Robin sequence is the preferred ...

Romana sign

Romana sign, also known as chagoma, refers to periorbital swelling, palpebral oedema and conjunctivitis seen 1-2 weeks following infection with Trypanosoma cruzi (causative agent in the Chagas disease).  Romana sign is associated with ipsilateral regional lymphadenopathy.  History and etymolog...

Rosai-Dorfman disease

Rosai-Dorfman disease (RDD), also known as sinus histiocytosis with massive lymphadenopathy (SHML), is a rare benign idiopathic proliferative disease that involves phagocytic histiocytes. Epidemiology The disease predominantly, occurs in young adults with a mean age at presentation of 21 years...

Updating… Please wait.

Alert accept

Error Unable to process the form. Check for errors and try again.

Alert accept Thank you for updating your details.