Hemangioblastomas can cause polycythemia due to ectopic production of erythropoietin as a paraneoplastic syndrome.

Hemangioblastoma are among the rarest central nervous system tumors, accounting for less than 2%. Hemangioblastomas usually occur in adults, yet tumors may appear in VHL syndrome at much younger ages. Men and women are approximately at the same risk. Although they can occur in any section of the central nervous system, they usually occur in either side of the cerebellum, the brain stem or the spinal cord.

Extraskeletal chondroma (also known as "Chondroma of soft parts") is a cutaneous condition, a rare benign tumor of mature cartilage.

A chondroma is a benign cartilaginous tumor, which is encapsulated with a lobular growing pattern.

Tumor cells (chondrocytes, cartilaginous cells) resemble normal cells and produce the cartilaginous matrix (amorphous, basophilic material).

Characteristic features of this tumor include the vascular axes within the tumor, which make the distinction with normal hyaline cartilage.

Based upon location, a chondroma can be described as an enchondroma or ecchondroma.

- enchondroma - tumor grows within the bone and expands it.

- ecchondroma - grows outward from the bone and this is rare.

Treatment

- best left alone

- if it causes fractures (enchondroma) or is unsightly it should be removed by curettage and the defect filled with bone graft.

An ecchondroma is a type of chondroma that is subperiosteal. A proliferation is known as "ecchondrosis".

Cartilage tumors form in Cartilage tissue. They can be either benign (Chondroma) or malignant (chondrosarcoma). Frequently these tumors appear in bone, and not in pre-existing cartilage tissue. In some cases tumors that formed in other tissues may produce a cartilage-like matrix, an example of this is the pleomorphic adenoma of the sexual reproduction salivary glands.

The majority of patients with neurocutaneous melanosis are asymptomatic and therefore have a good prognosis with few complications. Most are not diagnosed, so definitive data in not available. For symptomatic patients, the prognosis is far worse. In patients without the presence of melanoma, more than 50% die within 3 years of displaying symptoms. While those with malignancy have a mortality rate of 77% with most patients displaying symptoms before the age of 2.

The presence of a Dandy-Walker malformation along with neurocutaneous melanosis, as occurs in 10% of symptomatic patients, further deteriorates prognosis. The median survival time for these patients is 6.5 months after becoming symptomatic.

PTEN hamartoma syndrome comprises four distinct hamartomatous disorders characterised by genetic mutations in the PTEN gene; Cowden syndrome, Bannayan-Riley-Ruvalcaba syndrome, Proteus syndrome and Proteus-like syndrome. Although they all have distinct clinical features, the formation of hamartomas is present in all four syndromes. PTEN is a tumor suppressor gene that is involved in cellular signalling. Absent or dysfunctional PTEN protein allows cells to over-proliferate, causing hamartomas.

Cowden syndrome is an autosomal dominant genetic disorder characterised by multiple benign hamartomas (trichilemmomas and mucocutaneous papillomatous papules) as well as a predisposition for cancers of multiple organs including the breast and thyroid. Bannayan-Riley-Ruvalcaba syndrome is a congenital disorder characterised by hamartomatous intestinal polyposis, macrocephaly, lipomatosis, hemangiomatosis and glans penis macules. Proteus syndrome is characterised by nevi, asymmetric overgrowth of various body parts, adipose tissue dysregulation, cystadenomas, adenomas, vascular malformation.

Benign tumors are very diverse, and may be asymptomatic or may cause specific symptoms depending on their anatomic location and tissue type. They grow outwards, producing large rounded masses, which can cause what is known as a "mass effect". This growth can cause compression of local tissues or organs, which can cause many effects such as blockage of ducts, reduced blood flow (ischaemia), tissue death (necrosis) and nerve pain or damage. Some tumors also produce hormones that can lead to life-threatening situations. Insulinomas can produce large amounts of insulin leading to hypoglycemia. Pituitary adenomas can cause elevated levels of hormones such as growth hormone and insulin-like growth factor-1, which cause acromegaly; prolactin; ACTH and cortisol, which cause Cushings disease; TSH, which causes hyperthyroidism; and FSH and LH. Bowel intussusception can occur with various benign colonic tumors. Cosmetic effects can be caused by tumors, especially those of the skin, possibly causing psychological effects on the person with the tumor. Vascular tumors can bleed, which in some cases can be substantial, leading to anemia.

The majority of patients can be expected to be cured of their disease and become long-term survivors of central neurocytoma. As with any other type of tumor, there is a chance for recurrence. The chance of recurrence is approximately 20%. Some factors that predict tumor recurrence and death due to progressive states of disease are high proliferative indices, early disease recurrence, and disseminated disease with or without the spread of disease through the cerebral spinal fluid. Long-term follow up examinations are essential for the evaluation of the outcomes that each treatment brings about. It is also essential to identify possible recurrence of CN. It is recommended that a cranial MRI is performed between every 6–12 months.

The treatment for CGCG is thorough curettage. A referral is made to an oral surgeon. Recurrence ranges from 15%–20%. In aggressive tumors, three alternatives to surgery are undergoing investigation:

- corticosteroids;

- calcitonin (salmon calcitonin);

- interferon α-2a.

These therapeutic approaches provide positive possible alternatives for large lesions. The long term prognosis of giant-cell granulomas is good and metastases do not develop.

FNH is not a true neoplasm; it is believed to result from localized hyperplastic hepatocyte response to an underlying congenital arteriovenous malformation. It consists of normal liver constituents in an abnormally organized pattern, grows in a stellate pattern and may display central necrosis when large. Additionally evidence suggests that the incidence of FNH is related to oral contraceptive use.

Dermatofibromas are hard solitary slow-growing papules (rounded bumps) that may appear in a variety of colours, usually brownish to tan; they are often elevated or pedunculated. A dermatofibroma is associated with the dimple sign; by applying lateral pressure, there is a central depression of the dermatofibroma. Although typical dermatofibromas cause little or no discomfort, itching and tenderness can occur. Dermatofibromas can be found anywhere on the body, but most often they are found on the legs and arms. They occur most often in women; the male to female ratio is about 1:4. The age group in which they most commonly occur is 20 to 45 years.

Some physicians and researchers believe dermatofibromas form as a reaction to previous injuries such as insect bites or thorn pricks. They are composed of disordered collagen laid down by fibroblasts. Dermatofibromas are classed as benign skin lesions, meaning they are completely harmless, though they may be confused with a variety of subcutaneous tumours. Deep penetrating dermatofibromas may be difficult to distinguish, even histologically, from rare malignant fibrohistocytic tumours like dermatofibrosarcoma protuberans.

Dermatofibromas typically have a positive "buttonhole sign", or central dimpling in the center.

Central giant-cell granuloma (CGCG) is a benign condition of the jaws. It is twice as likely to affect women and is more likely to occur in 20- to 40-year-old people. Central giant-cell granulomas are more common in the mandible and often cross the midline.

Focal nodular hyperplasia (FNH) is a benign tumor of the liver (hepatic tumor), which is the second most prevalent tumor of the liver (the first is hepatic hemangioma). It is usually asymptomatic, rarely grows or bleeds, and has no malignant potential. This tumour was once often resected because it was difficult to distinguish from hepatic adenoma, but with modern multiphase imaging is usually now diagnosed by strict imaging criteria and not resected.

Benign fibrous histiocytomas (also known as dermal dendrocytoma, dermatofibroma, fibrous dermatofibroma, fibrous histiocytoma, fibroma simplex, nodular subepidermal fibrosis, and sclerosing hemangioma) are benign skin growths.

GISTs occur in 10-20 per one million people. The true incidence might be higher, as novel laboratory methods are much more sensitive in diagnosing GISTs. The estimated incidence of GIST in the United States is approximately 5000 cases annually. This makes GIST the most common form of sarcoma, which constitutes more than 70 types of cancer.

The majority of GISTs present at ages 50–70 years. Across most of the age spectrum, the incidence of GIST is similar in men and women.

Adult GISTs are rare before age 40. Pediatric GISTs are considered to be biologically distinct. Unlike GISTs at other ages, pediatric GISTs are more common in girls and young women. They appear to lack oncogenic activating tyrosine kinase mutations in both KIT and PDGFRA. Pediatric GISTs are treated differently than adult GIST. Although the generally accepted definition of pediatric GIST is a tumor that is diagnosed at the age of 18 years or younger, "pediatric-type" GISTs can be seen in adults, which affects risk assessment, the role of lymph node resection, and choice of therapy.

Once a patient with neurocutaneous melanosis becomes symptomatic, little can be done to improve prognosis as there is no effective treatment for the disorder. Most therapies are designed to treat the symptoms associated with the disorder, mainly those related to hydrocephalus. A ventriculoperitoneal shunt to relieve intracranial pressure is the preferred method.

Chemotherapy and radiotherapy have been shown to be ineffective in cases of neurocutaneous melanosis where malignancy is present. Additionally, due to the total infiltration of the central nervous system by these lesions, surgical resection is not a viable treatment option.

It has been demonstrated that early embryonic, post-zygotic somatic mutations in the NRAS gene are implicated in the pathogenesis of NCM. Recently, experimental treatment with MEK162, a MEK inhibitor, has been tried in a patient with NCM and progressive symptomatic leptomeningeal melanocytosis. Pathological studies with immunohistochemical and Western Blot analyses using Ki67 and pERK antibodies showed a potential effect of MEK inhibiting therapy. Further studies are needed to determine whether MEK inhibitors can effectively target NRAS-mutated symptomatic NCM.

Carney triad (CT) is characterized by the coexistence of three types of neoplasms, mainly in young women, including gastric gastrointestinal stromal tumor, pulmonary chondroma, and extra-adrenal paraganglioma. The underlying genetic defect remains elusive. CT is distinct from Carney complex, and the Carney-Stratakis syndrome.

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract. GISTs arise in the smooth muscle pacemaker interstitial cell of Cajal, or similar cells. They are defined as tumors whose behavior is driven by mutations in the KIT gene (85%), PDGFRA gene (10%), or BRAF kinase (rare). 95% of GISTs stain positively for KIT (CD117). Most (66%) occur in the stomach and gastric GISTs have a lower malignant potential than tumors found elsewhere in the GI tract.

Central neurocytoma, abbreviated CNC, is an extremely rare, ordinarily benign intraventricular brain tumour that typically forms from the neuronal cells of the septum pellucidum. The majority of central neurocytomas grow inwards into the ventricular system forming interventricular neurocytomas. This leads to two primary symptoms of CNCs, blurred vision and increased intracranial pressure. Treatment for a central neurocytoma typically involves surgical removal, with an approximate 1 in 5 chance of recurrence. Central neurocytomas are classified as a grade II tumor under the World Health Organization's classification of tumors of the nervous system.

Most optic nerve melanocytomas are small, black, and do not grow.

Carney (CT), named for J Aidan Carney, is considered to be a specific type of multiple endocrine neoplasia (MEN). The three classically associated tumors are a subset of gastric epithelioid leiomyosarcoma (it is now known that this subset is actually gastrointestinal stromal tumor arising from the interstitial cells of Cajal), pulmonary chondroma, and extra-adrenal paraganglioma.

The condition manifests more commonly in females. Multiple tumors in multiple organs in young patients, with occasional sibling involvement, suggested an inherited disorder, but the underlying genetic basis has not been identified.

In addition to these three classical tumors, there is an increased incidence of pheochromocytoma, esophageal leiomyoma and adrenocortical adenoma.

The original description employed the then-prevailing terminology of gastric epithelioid leiomyosarcoma. Subsequent advances in molecular biology have led to the current terminology of gastrointestinal stromal tumors (GISTs). However, there is limited evidence to suggest that the gastrointestinal stromal tumors (GIST) in Carney triad lack CD117 (c-kit) mutations (i.e., they are wild-type), and hence these GISTs may prove unresponsive to Gleevec.

Most optic nerve tumors (65 percent) are gliomas that occur somewhere along the anterior visual pathway.

Cysts derived from CNS tissues are very common in America. They are a subtype of cerebrovascular diseases, which are the third leading cause of death in America. Generally, CNS cysts are present in all geographic regions, races, ages, and sexes. However, certain types of CNS cysts are more prevalent in certain types of individuals than others. Some examples of incidence rates in specific types of cysts include:

- Arachnoid cysts are more prevalent in males than females

- Colloid cysts are more prevalent in adults

- Dermoid cysts are more prevalent in children under 10 years of age

- Epidermoid cysts are more prevalent in middle-aged adults