Patellar tumors are extremely rare. They can be either benign or malignant primary bone tumors, or metastases.
Patellar tumors represent just 0.1% of all primary bone tumors 1.
Patients may present with anterior knee pain and/or a palpable mass 1,3.
Pathological fractures are fractures that occur in abnormal bone.
The term pathological fracture is usually reserved through a malignancy, either benign or malignant, although it has been used in the setting osteomyelitis. It can be used in the setting of generalised metabolic bone...
A pedunculated intratracheal mass has a variety of differential diagnoses:
benign tumor, 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-gynecological masses, e.g. colorectal carcinom...
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 (CMR), partial metabolic response (PM...
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 tumor is a form of local invasion in which primary tumors 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 perineural ...
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 tumor refer to a subtype of pulmonary carcinoid tumors that arise within the periphery of the lung. They are considered less common than the more centrally-located bronchial carcinoid tumors.
Many patients tend to be asymptomatic 2. Presen...
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 tumor 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)...
Peritoneal metastases are a relatively common location for metastases, particularly from tumors of the abdomen and pelvis, that generally imply a poor prognosis, often with a significant impact on palliation 1.
If peritoneal metastases are of an epithelial origin (as most are) and ...
A mnemonic for permeative processes in bone is:
R: round cell tumors (Ewing sarcoma)
E: eosinophilic granuloma
M: metastases/myeloma/malignant fibrous histiocytoma
D: desmoid tumor
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 tumor of the adrenal gland, with characteristic clinical, and to a lesser degree, imaging features. The tumors 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 tumors, 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 tumor of the pineal region accounting for ~50% of all tumors, and the majority (~80%) of intracranial germ cell tumors.
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 metastasis is a rare site of metastatic disease. They usually occur concomitantly with leptomeningeal metastases.
This article will discuss metastatic lesions affecting only the pineal gland. For other intracranial metastatic locations, please refer to the main article on intracran...
Pineal parenchymal tumors with intermediate differentiation (PPTID) are, as the name suggests, tumors which fall between pineocytoma (well differentiated, WHO grade I) and pineoblastomas (poorly differentiated, WHO grade IV). They are considered WHO grade II or III tumors 2. Although these tumor...
Pituitary carcinomas are rare tumors 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 tumors 1.
Pituitary lymphoma is very rare, although lymphomatous (or leukemic) 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 genera...
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 tumor is greater than 10 mm in size, it is then co...
Abnormal nodular enhancement of the pituitary stalk can be seen in a number of entities.
granular cell tumor of the pituitary (pituitary choristoma)
pilocytic astrocytoma of the...
Pleomorphic adenomas, also known as benign mixed tumors (BMTs), are the most common salivary gland tumors.
On imaging, they commonly present as well circumscribed rounded masses, most commonly located within the parotid gland, hypoechogenic on ultrasound and bright on T2WI with homogeneous enha...
Pleomorphic carcinoma of the lung is a rare type of lung tumor. They are classified under sarcomatoid carcinomas of the lungs.
These tumors 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 tumor 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 neurofib...
POEMS syndrome is the acronymic name for a rare multisystem paraneoplastic disorder comprising of a minimum of three of the following features in the setting of a plasma cell dyscrasia:
hepatomegaly, splenomegaly or lymphadenopathy
The pool sign is a recently described brain MRI appearance where an intracranial mass exhibits a T2 hyperintense rim adjacent to a solid mass surrounded by peritumoral edema. This appearance has been recently suggested to be a feature characteristic of metastatic adenocarcinoma (with various pri...
Porocarcinoma (or eccrine porocarcinoma) is a rare type of malignant eccrine sweat gland tumor, more frequently encountered in the lower extremities (feet and legs). It arises from the intraepidermal portion of eccrine sweat glands or acrosyringium.
It represents 0.005-0.01% of all cutaneous tu...
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...
Preinvasive lesions for lung adenocarcinoma are a category of small non-invasive lung lesions which are closely related to adenocarcinoma of the lung. They may represent a spectrum of premalignant to low-grade malignant lesions.
The category includes two types of lesions:
atypical adenomatous ...
Primary benign cardiac tumors 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. Tumors include 1-2:
most common in adults
accounts for ~50% of all primary beni...
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 tumors and <1% of non-Hodgkin lymphoma.
PBL is defined as the presence of lymphoma isolated to one...
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 leukemia should not be present for at least 6 months after the liver tumor is detected (see: secondary hepat...
Primary intracranial leiomyosarcomas are primary malignant tumors derived from smooth muscle cell lineage in the cranial vault.
Primary intracranial leiomyosarcomas are extremely rare. Most commonly, these lesions have been described as EBV-associated smooth muscle tumors in patie...
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 the involvement of any other site. It is an extremely rare yet well-recognised condition.
POL accounts for ~1.5% of ovarian tumors 5.
The rarity of this condition is probably co...
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 tumors 4.
Primary pleural lymphoma may be Hodgkin or non-Hodgkin lymphoma with...
Primary melanoma of the prostate is rare, and usually cannot be diagnosed on imaging alone. In many cases, it is believed that in fact, the tumor represents prostatic involvement by melanoma of the urethra.
Primary malignant melanoma of the prostate represents both a tiny fraction...
Primary pulmonary lymphomas refer to clonal lymphoid proliferation affecting the lungs without any detectable extrapulmonary involvement. It is much rarer than secondary pulmonary lymphoma and is most frequently represented by lymphoma of B-cell lineage - often marginal zone B-cell lymphoma of m...
Primary pulmonary synovial sarcoma is an extremely rare tumor 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 tumor staging (T)
Tx: primary tumor cannot be assessed
T0: no evidence of primary tumor
Tis: carcinoma in situ
Ta: non-invasive papillary, polypoid, or verrucous carcinoma
T1: invasion of sube...
Melanoma of the urethra is a very rare tumor of the male urethra and often presents as an invasive prostatic mass. As such it is usually referred to as primary prostatic malignant melanoma.
Malignant uveal melanomas, also referred as choroidal melanomas, are the most common primary tumor 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 tumors increas...
Prostate cancer staging takes into account TNM (primary site, nodal and distant metastases), pretreatment PSA and histological grading. The Gleason score is used to determine the Grade Group.
Another, less used, staging system is the Jewett-Whitmore staging system.
Additionally, there is some...
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 tumor 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 tumor 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 eld...
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 radiological 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 before treatment, and with...
Pseudo Meigs syndrome refers to a clinical syndrome of pleural effusion, ascites associated with an ovarian tumor that is not a fibroma or a fibroma-like tumor.
Entities that have been reported to result in pseudo Meigs syndrome include
colon carcinoma metastases ...
Pseudomyxoma peritonei refers to the intraperitoneal accumulation of a gelatinous ascites secondary to rupture of a mucinous tumor. The most common cause is a ruptured mucinous tumor of the appendix/appendiceal mucocoele 10.
Occasionally, mucinous tumors of the colon, rectum, stomach, pancrea...
Pulmonary artery sarcomas are extremely rare tumors that originate from the intimal mesenchymal cells of the pulmonary artery. It is frequently misdiagnosed as pulmonary thromboembolism.
Primary malignant tumors of the pulmonary arteries are very rare with an incidence of 0.001–...
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 tumors via blood or lymphatics.
This article describes haematogenous pulmonary metastases with lymphangitis carcinomatosis discussed separately.
The epidemiology will match that of the u...
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 carcinogenesis is widely but not universally believed to occur at exposures from ionising radiation used in medical imaging. It is thought to be a stochastic effect of ionising radiation, with the linear no-threshold theory (LNT) proposing no "safe" level of radiation exposure,...
Radiation-induced cerebral vasculopathy encompasses a complex and broad range of effects on the intra- and extracranial vessels resulting from injury from radiation exposure. Manifestations can include hemorrhages and ischemic strokes, cavernoma and capillary telangiectasias, and large vessel st...
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 tumors with a poor prognosis when compared with primary sarcomas. Malignant fibrous histiocytoma and osteosarcoma are the two most common histologica...
Radiation-induced thyroid cancer is an important etiology 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-analyzes. Although these studies var...
Radioembolisation is the delivery of radioactive microspheres to cancers using an endovascular approach. It is often performed as an outpatient procedure.
hepatic metastases from colorectal carcinoma
Radiomics (as applied to radiology) is a field of medical study that aims to extract a large number of quantitative features from medical images using data-characterization algorithms. The data is assessed for improved decision support. It has the potential to uncover disease characteristics tha...
The raindrop skull appearance of calvarial multiple myeloma is the presence of multiple, well-defined lytic lesions (punched out lesions) of various size scattered throughout the skull. This term is applied as an analogy to rain hitting a surface and splashing, where it leaves a random pattern o...
Response assessment in neuro-oncology criteria (RANO), published in 2010 1, are used to assess response to first-line treatment of glioblastoma (as well as lower grade astrocytoma 3) and have largely superseded the older Macdonald criteria (which only dealt with glioblastoma multiforme) 2.
RASopathies are a class of developmental disorders caused by germline mutations in genes that encode for components or regulators of the Ras/mitogen-activated protein kinase (MAPK) pathway.
As a group, RASopathies represent one of the most common malformation syndromes, with an in...
Response Evaluation Criteria In Solid Tumors (RECIST) was updated to version 1.1 in 2009.
For both RECIST 1.0 and 1.1, the requirement for measurable disease at baseline depends on the endpoints of the clinical trial.
The fundamental concept common to both versions of RECIST is that measurable...
Rectal cancer, although sharing many of the features of generic colorectal carcinoma (CRC), has some features that make it unique. These are predominantly related to its anatomical location which has implications in both preoperative imaging assessment and surgical technique.
Demographics and c...
Staging strongly influences the success of and rate of local recurrence following rectal cancer resection. MRI is the modality of choice for the staging of rectal cancer, to guide surgical and non-surgical management options. MRI is used at diagnosis, following downstaging chemoradiotherapy, and...
Renal cell carcinomas (RCC) are primary malignant adenocarcinomas derived from the renal tubular epithelium and are the most common malignant renal tumor. They usually occur in 50-70-year old patients and macroscopic hematuria occurs in 60% of the cases.
On imaging, they have a variety of radi...
Renal cell carcinoma staging using the TNM staging system for renal cell carcinoma. Older but still widely used system in some practices is the Robson staging system.
TNM staging (7th edition)
T1a: tumor confined to kidney, <4 cm
T1b: ltumour confined to kidney, >4 cm but <7 cm
Renal leiomyomas are benign tumors of the kidney originating from smooth muscle cells of the renal capsule, pelvis, calyces, or blood vessels.
There is a 4-5.5% prevalence based on autopsy findings 1.
Renal leiomyomas are usually incidental findings. In symptomatic cases...
Renal lymphoma is usually a part component of multi-systemic lymphoma - primary renal lymphoma is unusual.
Typical imaging findings are multiple bilateral hypodense or infiltrative renal masses.
While renal lymphoma has an autopsy incidence of ~45% (range 30-60%) in lymphoma pati...
Renal oncocytomas are relatively benign renal tumors. The main clinical importance of this lesion is the difficulty in pre-operatively distinguishing it from renal cell carcinomas, as epidemiology, presentation, imaging and even histology can be very similar.
Renal oncocytomas ac...