Papillary cystadenomas of the epididymis are the second most common benign tumors of the epididymis after adenomatoid tumors and are common in patients with von Hippel-Lindau disease (vHL).
Papillary cystadenomas are usually asymptomatic.
They are more comm...
Papillary intralymphatic angioendothelioma (PILA) (also known - especially historically - as a Dabska tumor) is a rare, low-grade soft tissue tumor 1. The lesion is borderline-malignant and metastasis is distinctly unusual.
Less than 40 cases have been reported in the global liter...
Papillary meningiomas (PM) are a rare subtype of malignant (WHO grade III) meningiomas that tends to occur in young patients and are characterized by an aggressive growth pattern illustrated by atypical imaging features such as brain and bone invasion. These tumors have a strong tendency of recu...
Papillary thyroid carcinoma (PTC) is the most common malignancy of the thyroid gland and frequently has nodal metastases at presentation.
When the tumor measures <1 cm, the term micropapillary carcinoma (mPTC) is used 14.
Papillary thyroid cancer (as is the case wit...
Paragangliomas, sometimes called glomus tumors, are rare neuroendocrine tumors 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 f...
Paragangliomas of the head and neck are rare, representing <0.5% of all head and neck tumors. They arise in a number of locations along the carotid sheath and middle ear including the carotid bifurcation, vagal ganglia, jugular bulb, and tympanic plexus.
For a general discussion of the patholog...
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.
Parathyroid carcinomas are very rare, and the overwhelming majority of discrete parathyroid gland lesions seen will be parathyroid adenomas. Carcinomas often present with profound hyperparathyroidism, as most of them are functional. Early metastasis is not uncommon. Imaging is important in their...
Parathyromatosis (plural: parathyromatoses) is the very rare phenomenon in which there is hyperplasia of residual foci of parathyroidal soft tissue after surgical parathyroidectomy resulting in recurrent hyperparathyroidism.
Parathyromatosis is very rare, a study from 2012 stated ...
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...
Particle therapy (also known as hadronic therapy) is the generic term used for any type of external beam radiotherapy (EBRT) employing high-energy particles. Currently proton therapy accounts for most of this type of EBRT. Although strictly a form of particle therapy, electron therapy is usually...
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 and occur spontaneously or following minor trauma that would not otherwise fracture biomechanically normal bone.
The term pathological fracture is usually reserved for malignancies, either benign or malignant, althoug...
Pediatric cystic nephromas, previously known as multilocular cystic nephromas, are rare benign renal neoplasms occurring in children. As of the 2016 WHO classification, they are considered distinct from adult cystic nephromas 1,2.
Evolving terminology regarding cystic nephromas and...
A pedunculated intratracheal mass has a variety of differential diagnoses:
benign tumor, e.g. hamartoma, chondroma, 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
pelvic inflammatory disease
Extragynaecological masses, e.g. colorectal carcinoma, appendicular abscess, lymp...
Percutaneous ablation in the kidney is now performed as a standard therapeutic nephron-sparing option in patients who are poor candidates for resection. It can either be a radiofrequency ablation or a cryoablation.
Follow up time frame
Can vary according to center but usually includes contrast...
Percutaneous endoscopic gastrostomy (PEG) is a procedure where a flexible feeding tube (commonly known as a PEG tube) is inserted through the abdominal wall and into the stomach. This may be placed under endoscopic or radiological guidance, in the latter, the procedure may be known as a percutan...
Percutaneous liver tumor ablation techniques are well-established and effective therapeutic alternatives for the treatment of primary and secondary liver tumors. Hepatocellular carcinoma (HCC) and colorectal oligometastatic disease are the most common indications. There are specific indications ...
Perianal disease (also known as anorectal disease) is the collective name given to a group of diseases that primarily affect the anal canal +/- rectum. The disease spectrum ranges from the typically benign, e.g. hemorrhoids, to the potentially more serious, e.g. perianal fistula 1-3.
Pericardial mesothelioma refers to 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 p...
Perihilar cholangiocarcinoma staging is, for prognostication, most commonly conducted using the TNM staging classification of the American Joint Committee on Cancer (AJCC)/Union for International Cancer Control (UICC). As of 2018, the staging criteria are in their 8th edition and reflected below...
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-recognized 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...
Periosteal reaction, also known as periostitis or periosteitis, is a nonspecific radiographic finding that indicates periosteal irritation. Periosteal reactions may be broadly characterized as benign or aggressive, or more specifically categorized by pattern.
Benign versus aggre...
Peripheral primitive neuroectodermal tumors (pPNET) tend to be large and aggressive retroperitoneal tumors.
The imaging characteristics of peripheral PNETs are non-specific. However, they should be considered in the differential diagnosis of a large, aggressive retroperi...
Peripheral pulmonary carcinoid tumor refers 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. Prese...
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 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-...
Pheochromocytomas 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 a deep compartment of the head and neck, located between the fascia of the pharyngeal constrictor muscles (buccopharyngeal or visceral fascia) and the mucosal surface of the nasopharynx, oropharynx, and hypopharynx.
Not a true anatom...
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...
Pion therapy is a form of particle therapy employing pions. Pions, or to give them their full name, negatively-charged pi mesons (π-), are a type of meson. Pion therapy is currently not used as a treatment modality due to its great expense and lack of clinical efficacy 1,2.
Pituitary blastomas are a very rare type of pituitary tumor.
Pituitary blastomas typically affect children under 2 years old. They are almost pathognomonic for DICER1 syndrome and warrant testing for germ-line DICER1 mutation if found 1,2.
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 of the lacrimal glands, also known as benign mixed tumors (BMTs), are the most common lacrimal gland tumors.
slowly progressive and painless proptosis, with inferomedial displacement of the globe
visual disturbance possible with large tumors
Pleomorphic adenomas of the salivary glands, also known as benign mixed tumors (BMTs), are the most common salivary gland tumors. The salivary glands are the most common site of pleomorphic adenomas.
On imaging, they commonly present as well-circumscribed rounded masses, most commonly located w...
Pleomorphic carcinomas of the lung are a rare type of non-small cell lung carcinomas (NSCLC) 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 recognized association with smoki...
Pleomorphic hyalinizing angiectatic tumors (PHAT) of soft parts are locally recurring non-metastasizing neoplasms of intermediate biologic potential and are classified as soft tissue tumors of uncertain lineage.
Pleomorphic hyalinizing angiectatic tumors of soft parts a very rare ...
Pleomorphic liposarcomas are high-grade malignant neoplasms arising from adipocytic tissues characterized by a variable number of pleomorphic lipoblasts and the absence of areas of well-differentiated liposarcoma and other lines of differentiation.
Pleomorphic sarcomas are rare an...
Pleural involvement with lymphoma can occur in two situations:
primary pleural lymphoma
primary effusion lymphoma
secondary involvement of the pleura with lymphoma
Pleural metastases account for the vast majority of malignant lesions of the pleura and are more common than malignant mesothelioma.
The infiltration of the pleura usually manifests as pleural effusion, which is the first manifestation of pleural metastasis. In addition t...
Pleural pointillism is multiple high signal regions on b=1000 diffusion-weighted imaging but not at lower b-values. It can be a reliable tool allowing differentiation of malignant from benign pleural lesions and can help guide biopsy 1-3. Its sensitivity is reported to be 93-100% and specificit...
Pleuropulmonary blastomas 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. They are classified under sarcomatoid carcinomas of the lungs.
Plexiform fibrohistiocytic tumors (PFHT) are dermal or subcutaneous soft tissue neoplasms of uncertain behavior with biphasic tumor morphology and a plexiform growth pattern.
Plexiform fibrohistiocytic tumors are rare tumors. They can occur over a wide age range but are usually s...
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 localized 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...
Positron emission tomography (PET) is a modern non-invasive imaging technique for quantification of radioactivity in vivo. It involves the intravenous injection of a positron-emitting radiopharmaceutical, waiting to allow for systemic distribution, and then scanning for detection and quantificat...
Positron Emission Tomography Response Criteria in Solid Tumors (PERCIST) are guidelines to asses tumors that makes use of positron emission tomography (PET) to provide functional information to help determine tumor viability.
The criteria consist of four categories: complete metabolic response ...
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 ...
Preinvasive lesions of the lung are those pulmonary lesions that have not yet progressed to malignancy but have the potential to do so. This category includes:
squamous dysplasia (SD) of lungs: squamous cell carcinoma in situ (CIS) of lung
preinvasive adenocarcinoma of the lung 5,6
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 ben...
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 cardiac tumors are uncommon and comprise only a small minority of all tumors that involve the heart: most are mediastinal or lung tumors that extend through the pericardium and into the heart, or metastases 1.
Primary cardiac tumors have an estimated autopsy prevalence of ...
Primary colorectal small cell carcinoma (CrSmCC) is a very rare neuroendocrine tumor with an aggressive course.
Neuroendocrine carcinomas comprise less than 1% of all colorectal cancer.
As with other small cell carcinomas, they are malignancies derived from neuroendocr...
Primary cutaneous lymphomas represent a group of extranodal non-Hodgkin lymphomas (T- or B-cell) primarily confined to the skin with no evidence of extracutaneous disease at the time of diagnosis (cf. secondary involvement of the skin).
Mycosis fungoides is the most prevalent type of primary c...
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, with 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 hepatic lympho...
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%
nasopharyngeal papillary adenocarcinoma
adenoid cystic carcinoma
Primary mediastinal large B-cell lymphoma is a distinct entity, recognized 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 non-cutaneous melanomas are much less common than primary cutaneous melanomas 1. These include
primary uveal malignant melanoma
primary prostatic malignant melanoma
primary urethral malignant melanoma
sinonasal mucosal melanoma
Primary osteosarcoma of the breast, a.k.a. extraskeletal osteosarcoma of breast, is an uncommon breast malignancy and is a subtype of extraskeletal osteosarcoma.
While it can present in a wide are group, the peak age at presentation is around the 6th decade 7.
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-recognized condition.
POL accounts for ~1.5% of ovarian tumors 5.
The rarity of this condition is probably in...
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 chondrosarcoma is an extremely rare form of chondrosarcoma, in terms of location. The majority of intrathoracic chondrosarcomas occur in relation to the chest wall.
While the exact incidence is unknown, only a handful of cases have been reported in the literature...
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...
A primary pulmonary meningioma is a very rare from of an ectopic meningioma.
They are generally asymptomatic and incidentally discovered although rarely patients with symptoms have also been reported.
Histologically, they comprise of whorls of spindle cells int...
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 rare and poorly differentiated types of non-small cell lung carcinomas (NSCLC).
They are thought to account for 0.2 to 1% of all lung cancers 1. Sarcomatoid histology may be present in 0.1-0.4% of non-sma...
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 to 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 incr...
Prostate cancer ranks as the most common primary 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...
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.
An old, superseded staging system is the Whitmore-Jewett staging system.
Additionally, there is some ...
PI-RADS (Prostate Imaging–Reporting and Data System) is a structured reporting scheme for multiparametric prostate MRI in the evaluation of suspected prostate cancer in treatment naive prostate glands. This article reflects version 2.1 (v2.1), published in 2019 and developed by an internationall...
Prostate MRI has become an increasingly frequent examination faced in daily radiological practice and is mainly conducted for the detection, active surveillance and staging of prostate cancer. This approach is an example of how to create a radiological report of a prostate MRI with consideration...