Optic nerve meningiomas are benign tumours arising from the arachnoid cap cells of the optic nerve sheath, and represent ~20% of all orbital meningiomas, the majority of which are direct extensions from intracranial meningiomas.
These tumours typically appear as masses within the optic nerve, ...
Orbital metastases are relatively uncommon, but some primary tumours do have a predilection to metastasise to the orbit.
This article concerns itself with extraocular metastases, rather than intraocular tumours or direct extension of tumours from neighbouring regions. For a discussion of intrao...
Orbital pathology covers a variety of diverse diseases that affect the orbit. The complicating factor is that the orbit is composed of a large number of different tissues which each have a plethora of pathologies that can affect them.
For simplification, they can be separated i...
Osteopoikilosis is a sclerosing bony dysplasia characterised by multiple benign enostoses. It is a rare inherited benign condition incidentally found on skeletal x-rays. Its importance is predominantly in correct diagnosis so that it is not mistaken for pathology.
The bone islands...
The most commonly adopted ovarian cancer staging system is the FIGO staging system. The most recent staging system is from 2014 1:
CT is considered the best imaging modality for staging ovarian cancer. 4.
stage I: tumour limited to the ovary or fallopian tube
tumour limited to o...
Ovarian thecomas are benign ovarian tumours of sex cord / stromal (mesenchymal) origin. They are thought to account for approximately 0.5-1% of all ovarian tumours. As ovarian thecomas secrete oestrogen, they are described as functional ovarian tumours.
They typically present in o...
Ovarian transposition is a surgical procedure in which the ovaries are displaced from the pelvis before pelvic radiation therapy in order to protect them from radiation injury.
It is performed in premenopausal women with a variety of pelvic malignancies (e.g cervical cancer, rectal cancer, and ...
Paget disease of the breast, which is also known as Paget disease of the nipple, has traditionally been described as a form of breast malignancy characterised by infiltration of the nipple epidermis by malignant cells. Although most cases have underlying focus or foci of in situ or invasive carc...
Pancreatic calcifications can arise form many aetiologies.
Punctate intraductal calcifications
acute alcoholic pancreatitis (20-40%)
intraductal, numerous, small, irregular
preponderant cause of diffuse pancreatic intraductal calcification
idiopathic: no underlying ca...
Pancreatic ductal adenocarcinoma makes up the vast majority (~90%) of all pancreatic neoplasms and remains a disease with a very poor prognosis and high morbidity.
On imaging, it usually presents as a hypodense mass on CT that is poorly marginated, which may encase vessels and the common biliar...
Staging of pancreatic ductal adenocarcinoma is traditionally done according to American Joint Committee on Cancer (AJCC) / Union for International Cancer Control (IUCC) TNM system. In 2017 new edition (8th edition) AJCC published with some major changes; now exocrine and endocrine tumours of th...
Pancreatic lymphoma is most commonly a B-cell sub-type of non-Hodgkin lymphoma.
Typically seen in middle-aged patients: mean of 55 years; range, 35-75 years and in immunocompromised patients.
Presentation is often non-specific. reported symptoms include 1:
Pancreatic mesenchymal neoplasms (or pancreatic nonepithelial neoplasms) are a group of rare pancreatic neoplasms that arise from the structural elements of the pancreas (nerves, fat, lymph), rather than from the exocrine or endocrine cells of the pancreas. Neoplasms from exocrine and endocrine ...
There are numerous primary pancreatic neoplasms, in part due to the mixed endocrine and exocrine components.
Classification based on function
exocrine: ~99% of all primary pancreatic neoplasms
pancreatic ductal adenocarcinoma ~90-95%
intraductal papillary muc...
Pancreatoblastomas are rare paediatric tumours of the pancreas. However, they are the most common pancreatic neoplasm of childhood and are often associated with a raised alpha-fetoprotein.
There is slight male predilection. Usually occurs in the first decade of life with a mean ag...
Papillary carcinoma of the breast is a rare ductal breast malignancy.
They are thought to account for 1-2% of breast carcinomas 2. They typically present in postmenopausal patients with the mean age at being ~63-67 years.
A papillary carcinoma may manifest ...
Papillary cystadenomas of the epididymis are the second most common benign tumours of the epididymis after adenomatoid tumours and are common in patients with von Hippel-Lindau disease (vHL).
Papillary cystadenomas are usually asymptomatic.
They are more co...
Papillary meningiomas (PM) are a rare subtype of malignant (WHO grade III) meningiomas that tends to occur in young patients and are characterised by an aggressive growth pattern illustrated by atypical imaging features such as brain and bone invasion. These tumours have a strong tendency of rec...
Paragangliomas, sometimes called glomus tumours, are rare neuroendocrine tumours arising from paraganglia.
Paraganglia are clusters of neuroendocrine cells dispersed throughout the body and closely related to the autonomic nervous system, with either parasympathetic or sympathetic...
Paraneoplastic syndromes occur secondary to the indirect effects of a malignancy and occur remotely to the primary malignancy. Symptoms are mediated by cytokines, hormones or immune cross-reactivity. These syndromes can cause a diverse range of symptoms and can affect multiple systems.
Parotid enlargement (also known as parotidomegaly) has a wide differential given the significant breadth of pathology that can affect the parotid gland. These can be separated by the standard surgical sieve approach into infective, inflammatory, immune, neoplastic, infiltrative, and congenital c...
Patellar tumours are extremely rare. They can be either benign or malignant primary bone tumours, or metastases.
Patellar tumours represent just 0.1% of all primary bone tumours 1.
Patients may present with anterior knee pain and/or a palpable mass 1,3.
A pedunculated intratracheal mass has a variety of differential diagnoses:
benign tumour, e.g. hamartoma, chrondroma, lipoma
metastasis to tracheal mucosa, e.g. renal cell carcinoma, melanoma
polyp, e.g. inflammatory, antrochoanal
Pelvic masses in females carry a broad differential diagnosis:
benign adnexal cyst: 34%
pelvic malignancy: 14%
pelvic inflammatory disease: 8%
Extra-gynaecological masses, e.g. colorectal carcino...
Pepperpot skull is occasionally used in place of salt and pepper skull to describe the typical radiographic appearance of multiple small radiolucent lesions of the skull vault.
This is classically seen in hyperparathyroidism 2, and is occasionally used (inaccurately) to describe the raindrop sk...
Positron Emission Tomography Response Criteria in Solid Tumors (PERCIST) make use of positron emission tomography (PET) to provide functional information to help determine tumor viability.
The criteria consist of four categories: complete metabolic response, partial metabolic response, progress...
Pericardial mesothelioma refers to a mesothelioma arising primarily from the pericardium.
They are rare and are only thought to account for ~0.7% of all malignant mesotheliomas. There is male to female predominance of approximately 3:1.
The presentation of...
Perineural spread of tumour is a form of local invasion in which primary tumours cells spread along the tissues of the nerve sheath. It is a well-recognised phenomenon in head and neck cancers.
An important distinction has to be made between perineural invasion (PNI) and perineura...
Periosteal osteosarcoma is a form of surface osteosarcoma.
It is the second most common type of juxtacortical or surface osteosarcoma after parosteal osteosarcoma and accounts for 1.5% of all osteosarcoma cases. It affects a slightly older age group (10-20 years) cf. conventional...
Peripheral pulmonary carcinoid tumour refer to a subtype of pulmonary carcinoid tumours that arise within the periphery of the lung. They are considered less common than the more centrally-located bronchial carcinoid tumours.
Many patients tend to be asymptomatic 2. Pre...
Peritoneal calcification is seen in a limited number of conditions that result in calcification of peritoneal structures. Therefore, the differential diagnosis is small:
psammoma bodies in malignancy (most frequently cystadenocarcinoma of the ovary): fine sand-like calcification
Peritoneal mesothelioma is an uncommon primary tumour of the peritoneal lining. It shares epidemiological and pathological features with but is less common than its pleural counterpart, which is described in detail in the general article on mesothelioma. Other subtypes (also discussed separately...
A mnemonic for permeative processes in bone is:
R: round cell tumours (Ewing sarcoma)
E: eosinophilic granuloma
M: metastases/myeloma/malignant fibrous histiocytoma
D: desmoid tumour
permeative process in bone
PET-CT is a combination of cross-sectional anatomic information provided by CT and the metabolic information provided by positron emission tomography (PET).
PET is most commonly performed with 2-[F-18]fluoro-2-deoxy-D-glucose (FDG). Fluorine-18 (F-18) is an unstable radioisotope and has a half-...
Phaeochromocytomas are an uncommon tumour of the adrenal gland, with characteristic clinical, and to a lesser degree, imaging features. The tumours are said to follow a 10% rule:
~10% are extra-adrenal
~10% are bilateral
~10% are malignant
~10% are found in children
~10% are familial
The pharyngeal (or superficial) mucosal space is one of the seven deep compartments of the head and neck. It consists of the mucosa and structures deep to the mucosa of the nasopharynx, the oropharynx, and the laryngopharynx.
The pharyngeal mucosal space is the most internal comp...
Pilomyxoid astrocytomas are an uncommon and aggressive variant of pilocytic astrocytoma with unique clinical and histopathologic characteristics.
Pilomyxoid astrocytomas are usually encountered in young children and infants (mean age of 10-18 months), however, adults cases have be...
Pineal cysts are common, usually asymptomatic, and typically found incidentally. Their importance is mainly in the fact that they cannot be distinguished from cystic tumours, especially when large or when atypical features are present. As such, many patients undergo prolonged follow-up for these...
Pineal germinomas are the most common tumour of the pineal region accounting for ~50% of all tumours, and the majority (~80%) of intracranial germ cell tumours.
There is a marked male predominance with a M:F of ~13:1. Most patients are 20 years or younger at the time of diagnosis...
Pineal gland metastases are rare and mostly related to primary carcinomas of the lungs, breast, gastrointestinal tract, and kidneys. They usually occur concomitantly with leptomeningeal metastases.
This article will discuss metastatic lesions affecting only the pineal gland. For other intracr...
Pineal parenchymal tumours with intermediate differentiation (PPTID) are, as the name suggests, tumours which fall between pineocytoma (well differentiated, WHO grade I) and pineoblastomas (poorly differentiated, WHO grade IV). They are considered WHO grade II or III tumours 2. Although these tu...
Pituitary carcinomas are rare tumours indistinguishable from pituitary adenomas on imaging and defined only by the presence of central nervous system or systemic metastases.
The incidence is estimated at less than 0.5% of the pituitary symptomatic tumours 1.
Pituitary lymphoma is very rare, although lymphomatous (or leukaemic) infiltration of the perisellar dura is not infrequently encountered as part of more widespread CNS disease. This article concerns itself with involvement of the pituitary itself rather than the region more broadly. For a gener...
Pituitary metastases are rare, and unless a systemic metastatic disease is already apparent, are often preoperatively misdiagnosed as pituitary adenomas.
This article will discuss metastatic lesions affecting only the pituitary gland. For other intracranial metastatic locations, please refer t...
Pituitary microadenomas are a minority of all pituitary adenomas, but can pose imaging and management challenges on account of their size and protean clinical presentations.
By definition, a microadenoma is less than 10 mm in size. If the same tumour is greater than 10 mm in size, it is then c...
Abnormal nodular enhancement of the pituitary stalk can be seen in a number of entities.
granular cell tumour of the pituitary (pituitary choristoma)
pilocytic astrocytoma of t...
Pleomorphic carcinoma of the lung is a rare type of lung tumour. They are classified under sarcomatoid carcinomas of the lungs.
These tumours are thought to account for 0.1-0.4% of all lung malignancies.
There is a recognised association with smoking.
Pleural involvement with lymphoma can occur in two situations:
primary pleural lymphoma
primary effusion lymphoma
secondary involvement of the pleura with lymphoma
Pleural metastases are one of the vast majority of malignant lesions of the pleura.
The infiltration of the pleura usually manifests as pleural effusion, which is the first manifestation of pleural metastasis. In addition to the symptoms and systemic manifestations of neo...
Pleuropulmonary blastomas (PPB) are a rare, variably aggressive, childhood primary intrathoracic malignancy. In up to 25% of cases, the mass can be extrapulmonary with attachment to the parietal pleura.
PPB is encountered in childhood, mostly in the first years of life (90% in th...
Plexiform neurofibroma is an uncommon variant of neurofibroma, a benign tumour of peripheral nerves (WHO grade I), arising from a proliferation of all neural elements. Plexiform neurofibromas are essentially pathognomonic of neurofibromatosis type 1 (NF1). Unlike small sporadic localised neurofi...
Post surgical breast scar is a benign complication that usually occurs following surgical intervention to breast tissue. It can however be a strong and potentially very confusing mimicker of breast malignancy.
Review of the patient's past history and previous mammography...
Primary benign cardiac tumours are much less common than secondary metastatic deposits. However they are more likely when a cardiac mass is seen outside of the setting of terminal metastatic disease. Tumours include 1-2:
most common in adults
accounts for ~50% of all primary be...
Primary bone (skeletal/osseous) lymphoma (PBL) is a less common manifestation of lymphoma than secondary involvement from disseminated lymphoma. It is rare, accounting for <5% of bone tumours and <1% of non-Hodgkin lymphoma.
PBL is defined as the presence of lymphoma isolated to on...
Primary breast chondrosarcoma is a rare type of sarcoma that originates from the mammary stroma and not from the underlying bone or cartilage of the chest wall.
The prevalence of primary breast chondrosarcoma is reported to be 0.5-1%, they represent <5% of all sarcomas 1,14.
Primary cutaneous melanoma is the most common subtype of malignant melanoma, a malignant neoplasm that arises from melanocytes. Melanocytes predominantly occur in the basal layer of the epidermis but do occur elsewhere in the body. Primary cutaneous melanoma is by far the most common type of pri...
Primary hepatic lymphoma (PHL) is rare accounting for roughly 100 described cases. If it is being considered as a diagnosis, distal lymphadenopathy, splenomegaly, bone marrow disease, and leukaemia should not be present for at least 6 months after the liver tumour is detected (see: secondary hep...
There are a number of primary malignancies of the nasopharynx:
nasopharyngeal carcinoma (squamous cell carcinoma): 70%
lymphoma (sinonasal lymphoma): 20%
adenoid cystic carcinoma
Primary mediastinal large B-cell lymphoma is a distinct entity, recognised in the WHO classification of lymphoma.
Primary mediastinal large B-cell lymphoma accounts approximately 5% of large B-cell lymphoma, which is usually disseminated or found in the abdomen. There appears to b...
Primary ovarian lymphoma (POL) refers to involvement of the ovary with lymphoma but without involvement of any other site. It is an extremely rare yet well recognised condition.
POL accounts for ~1.5% of ovarian tumours 5.
The rarity of this condition is probably contr...
Primary pleural lymphoma is extremely rare, especially in immunocompetent patients.
Primary pleural lymphoma accounts for <0.5% of all non-Hodgkin lymphoma 2 and ~2.5% of primary chest wall tumours 4.
Primary pleural lymphoma may be Hodgkin or non-Hodgkin lymphoma wit...
Primary pulmonary lymphoma (PPL) refers to a clonal lymphoid proliferation affecting the lungs without any detectable extrapulmonary involvement. It is a much rarer type of pulmonary lymphoma and is most frequently represented by lymphoma of B cell lineage - often marginal zone B-cell lymphoma o...
Primary pulmonary synovial sarcoma is an extremely rare tumour and refers to a situation where a synovial sarcoma arises from the lung as a primary site. It together with a pleural synovial sarcoma comes under the broader category of pleuro-pulmonary synovial sarcomas 3.
Primary sarcomatoid carcinomas of the lung refer to a heterogeneous group of non-small cell lung carcinomas (NSCLC).
They are thought to account for 0.2 to 1% of all lung cancers 1. A sarcomatoid histology may be present in 0.1-0.4% of non-small cell lung cancers 3.
Primary urethral cancer, in most cases a urethral carcinoma, is a rare urological malignancy. It can be divided in female urethral cancer and male urethral cancer.
It has an incidence of 4.3 per million for males and 1.5 per million for females. It usually manifests in the fifth d...
Primary urethral cancer staging often uses the TNM system and is as follows:
Primary tumour staging (T)
Tx: primary tumour cannot be assessed
T0: no evidence of primary tumour
Tis: carcinoma in situ
Ta: non-invasive papillary, polypoid, or verrucous carcinoma
T1: invasion of s...
Melanoma of the urethra is a very rare tumour of the male urethra, and often presents as an invasive prostatic mass. As such it is usually referred to as primary prostatic malignant melanoma.
primary cutaneous melanoma
primary non-cutaneous melanoma
Malignant uveal melanomas, also referred as choroidal melanomas, are the most common primary tumour of the adult eye 3.
Malignant melanoma of the uvea is the most common primary intraocular malignancy and is predominantly seen in Caucasians 5. The incidence of these tumours incre...
Prostate cancer staging can be thought of in terms of physical location or grading histologically. The TNM classification is used to determine spread, and the Gleason score is used to determine the histological type. Another staging system is the Jewett-Whitmore staging system.
PI-RADS (Prostate Imaging Reporting and Data System) refers to a structured reporting scheme for evaluating the prostate for prostate cancer. It is designed to be used in a pre-therapy patient.
The original PI-RADS score was annotated, revised and published as the second version, PI-RADS v2 6, ...
Prostate specific antigen (PSA) is currently used as a tumour marker for prostate adenocarcinoma.
PSA is a 33 kilodalton glycoprotein produced in prostate epithelial cells. Its normal physiologic role is as a liquefying agent for seminal fluid; only a tiny amount leaks into the blood, therefore...
Prostate-specific membrane antigen (PSMA) (also known as glutamate carboxypeptidase II) is a type II transmembrane glycoprotein that has become an increasingly prominent imaging biomarker 1. PSMA has emerged as a useful target in PET imaging of prostate cancer, especially in the evaluation of sm...
Prostatic carcinoma ranks as the most common malignant tumour in men and the second most common cause of cancer-related deaths in men. Prostatic adenocarcinoma is by far the most common histological type and is the primary focus of this article.
It is primarily a disease of the el...
Protoplasmic astrocytoma is a rare variant of diffuse low-grade astrocytomas with histological and imaging features which overlap with other entities.
Until recently they were classified as a subtype of low-grade diffuse astrocytoma, however, in the latest (2016) update to WHO classification o...
The PSA density (PSAD), is a calculation performed at diagnosis and is the serum PSA level divided by the volume of the prostate gland.
PSA density has been used as a prognostication tool in helping decide between a watch-and-wait or an invasive approach when managing prostate carcinoma. The c...
Pseudocirrhosis is a term used to recapitulate imaging findings of cirrhosis, but occurring in the setting of hepatic metastases. It is most commonly reported following chemotherapeutic treatment of breast cancer metastases, although has also been reported prior to treatment, and with other mali...
Pseudo Meigs syndrome refers to a clinical syndrome of pleural effusion, ascites associated with an ovarian tumour that is not a fibroma or a fibroma-like tumour.
Entities that have been reported to result in pseudo Meigs syndrome include
colon carcinoma metastas...
Pseudomyxoma peritonei refers to the intraperitoneal accumulation of a gelatinous ascites secondary to rupture of a mucinous tumour. The most common cause is a ruptured mucinous tumour of the appendix/appendiceal mucocoele 10.
Occasionally, mucinous tumours of the colon, rectum, stomach, panc...
Pulmonary artery sarcomas are extremely rare tumours that originate from the intimal mesenchymal cells of the pulmonary artery. It is frequently misdiagnosed as pulmonary thromboembolism.
Primary malignant tumours of the pulmonary arteries are very rare with an incidence of 0.00...
Pulmonary lymphoma refers to lung parenchymal involvement with lymphoma.
It can be broadly divided as primary or secondary.
primary pulmonary lymphoma: (rare) usually non-Hodgkin lymphoma which is limited to the lung with or without mediastinal lymph node involvement and with no evi...
Pulmonary metastases are common and the result of metastatic spread from a variety of primary tumours via blood or lymphatics.
This article describes haematogenous pulmonary metastases with lymphangitis carcinomatosis discussed separately.
The epidemiology will match that of the ...
Pulmonary opacification represents the result of a decrease in the ratio of gas to soft tissue (blood, lung parenchyma and stroma) in the lung. When reviewing an area of increased attenuation (opacification) on a chest radiograph or CT it is vital to determine where the opacification is. The pat...
Pure ground glass lung nodules are a subtype of ground glass lung nodules where there is no associated solid component.
They have been shown to represent various pathologies such as 1,3
adenocarcinoma in situ of lung
minimally-invasive adenocarcinoma of lung
invasive adenocarcinoma of lung
Radial scar, or complex sclerosing lesion, is a rosette-like proliferative breast lesion. It is not related to surgical scarring. Some authors, however, reserve the latter term to lesions over 1 cm 5.
It is an idiopathic process with sclerosing ductal hyperplasia.
Its significance is that it...
Radiation-induced cerebral vasculopathy encompasses a complex and broad range of effects on the intra- and extracranial vessels resulting from injury from radiation exposure.
Clinical symptoms are broad and depend on the underlying vasculopathy. Radiation-induced telangie...
Radiation-induced gliomas are a rare complication of cranial irradiation, occurring in less than 3% of cases 15 years post treatment. Glioblastomas correspond to three-quarters of all radiation induced gliomas.
The risk of developing a secondary CNS cancer following radiation exposure has been...
Radiation-induced heart disease, also known as radiation cardiotoxicity, describes an uncommon constellation of potential cardiac complications of mediastinal radiotherapy.
The demographics of patients affected by radiation-induced heart disease are those of the underlying conditi...
Radiation-induced lung cancers have been reported as a rare late complication of radiation therapy in both post-operative breast cancer and Hodgkin lymphoma patients. These occur 5-10 years (or later) after treatment 1-4. There appears to be increased risk of lung cancer in these patients if the...
Radiation-induced neuritis is a complication of radiotherapy that may present with visible changes on MRI. It is likely to be most relevant in the head and neck region. There is only scarce radiology literature on the subject; radiation-induced optic neuritis is best documented.
Radiation-induced pulmonary fibrosis is the late manifestation of radiation-induced lung disease (RILD) and is relatively common following radiotherapy for chest wall or intrathoracic malignancies.
This article does not deal with changes seen in the acute phase. Please refer to the article on r...
Radiation-induced sarcoma (RIS) can originate in either the irradiated bone or soft tissues after a period of latency. They are usually high-grade tumours with a poor prognosis when compared with primary sarcomas. Malignant fibrous histiocytoma and osteosarcoma are the two most common histologic...
Radiation-induced thyroid cancer is an important aetiology of thyroid cancer.
Information about radiation induced thyroid malignancies comes from several long-term cohort studies along with some case controlled studies and their subsequent meta-analyses. Although these studies va...
Radiomics is a new emerging field in which medical images are converted into multidimensional data by data-characterisation algorithms. The data is assessed for improved decision support. Radiomics has the potential to uncover disease characteristics that fail to be recognised by the naked human...