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...
Oropharyngeal squamous cell carcinoma (OPSCC) is the most common type of head and neck cancer in the Western world 1. Typically it will be further categorized based on the specific anatomical location involved within the oropharynx, as this may affect prognosis and modality of treatment.
Osteopoikilosis is a sclerosing bony dysplasia characterized 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 ovarian-adnexal reporting and data system (O-RADS) is an ultrasound risk stratification and management system for the evaluation of ovarian and other adnexal masses.
These recommendations function have been published to guide the management of "average-risk patients without acute symptoms" ...
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: tumor limited to the ovaries
tumor limited to one ovary
Ovarian embryonal carcinomas are rare and malignant germ cell tumors of the ovary.
It is found predominantly in children and adolescents (average age 14 years).
Precocious puberty or menstrual irregularity occurs in 60% 2. The tumor can secrete beta-hCG and...
Ovarian Sertoli-Leydig cell tumors (SLCT), also known as an ovarian androblastomas, are a subtype of ovarian sex cord-stromal tumor.
They are rare and only account for ~0.5% of all ovarian tumors. While they can present at any age, they typically present <30 years old, with a mean...
Ovarian thecomas are benign ovarian tumors of sex cord / stromal (mesenchymal) origin. They are thought to account for approximately 0.5-1% of all ovarian tumors. As ovarian thecomas secrete estrogen, they are described as functional ovarian tumors.
They typically present in older...
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 ...
p16 is a widely used immunohistochemical marker indicating expression of the cell cycle protein cyclin-dependent kinase inhibitor 2A, which is upregulated by human papillomavirus (HPV) infection. In the uterine cervix, p16 positivity supports the diagnosis of a high-grade squamous intraepithelia...
Pediatric renal tumors and masses are another group of diseases (just like cystic renal diseases in both the adult and child) that are bewildering in their number, nomenclature and overlapping findings.
Wilms tumor: common in older children 1-8 years old
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 characterized by infiltration of the nipple epidermis by malignant cells. Although most cases have underlying focus or foci of in situ or invasive carc...
Pancoast tumor, also known as superior sulcus tumor, refers to a relatively uncommon situation where a primary lung cancer arises in the lung apex and invades the surrounding soft tissues. Classically a Pancoast syndrome results, but in actuality this is only seen in one quarter of cases.
Pancreatic calcifications can arise from many etiologies.
Punctate intraductal calcifications
alcoholic pancreatitis (20-40%) 2
intraductal, numerous, small, irregular
preponderant cause of diffuse pancreatic intraductal calcification
gallstone pancreatitis (2%) 2
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 bile d...
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 tumors of the...
Pancreatic lymphoma is most commonly a B-cell sub-type of non-Hodgkin lymphoma.
Pancreatic lymphoma is typically seen in middle-aged patients with a mean age of around 55 years old and is more common in immunocompromised patients.
Symptoms are often non-spe...
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 ...
Pancreatic metastases are uncommon and are only found in a minority (3-12%) of patients with widespread metastatic disease at autopsy. They account for only 2-5% of all pancreatic malignancies.
Demographics will match those of the primary tumor, but in general, will be in elderly ...
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 pediatric tumors 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 age ...
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 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...
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...
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...
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.
The term pathological fracture is usually reserved for malignancies, either benign or malignant, although it has been used in the setting of osteomyelitis. It can be used in the setting of generalized metabolic bone ...
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, 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...
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...
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 more potentially more serious, e.g. perianal fistula 1-3.
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-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 non specific radiographic finding that occurs with periosteal irritation. Periosteal reactions may be broadly characterized as benign or aggressive, or more specifically broken down by pattern.
Benign versus ag...
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 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 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 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 recognized 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 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...
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 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) 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 (CMR), partial metabolic response (P...
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 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 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 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 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...
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 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.