Nuchal-type fibroma is a rare benign proliferation involving the dermis and subcutaneous tissues, that is a collection of dense, hypocellular bundles of collagen with entrapped adipocytes and increased numbers of small nerves. It is no longer called a nuchal fibroma, but instead a "nuchal-type fibroma" since it develops in other anatomic sites. There is no known etiology. The World Health Organization, 2020, classified nuchal fibromas as a specific tumor form in the category of benign fibroblastic and myofibroblastic tumors. Signs and symptoms
These lesions are generally asymptomatic, although patients give a long history of a solitary, superficial mass. The mass is usually in the neck (hence the name "nuchal-type"), but it can be seen in the extremities, lumbosacral area, buttocks, and face. There is a strong association with diabetes mellitus and Gardner syndrome; in fact, it may be the initial manifestation of Gardner syndrome. Pathology
The tumors are unencapsulated and poorly circumscribed, showing a firm, white cut surface. Most tumors are about 3.5 cm, but can be up to 8 cm. By microscopic examination, there are haphazardly arranged thick collagen fibers, with a low cellularity and no pleomorphism. There are usually entrapped fat cells, skeletal muscle, and peripheral nerves. The may be perineural fibrosis. The elastic fibers may be altered, which is why an elastofibroma is considered in the differential diagnosis. Immunohistochemistry
The tumor cells are strongly positive for vimentin, CD34, and sometimes with CD99. There is often (up to 2/3rds) a nuclear reaction with β-catenin.
The pathogenesis of PSC remains unclear but probably involves a combination of environmental factors and genetic predisposition. Notably, 70-80% of patients with PSC are comorbid with inflammatory bowel disease (e.g., ulcerative colitis or Crohns colitis), suggesting there exists a link between the two.PSC predominantly affects males (60-70%) of 30–40 years of age. The disease has an incidence is 0.4-2.0 cases/100,000 and a prevalence of 16.2 cases/100,000, making it a rare disease. Nonetheless, PSC accounts for 6% of liver transplants in the US due to its eventual progression to end-stage liver disease, with a mean transplant-free survival of 21.3 year.Though 40-50% of patients are asymptomatic, commonly reported symptoms include abdominal pain in the right upper quadrant, pruritus, jaundice, fatigue, and fever. The most common signs are hepatomegaly and splenomegaly. Prolonged cholestasis in PSC may cause fat-soluble vitamin deficiency leading to osteoporosisDiagnosis requires elevated serum alkaline phosphatase persisting for at least 6 months and the presence of bile duct strictures on cholangiogram. Unlike primary biliary cholangitis, PSC lacks a diagnostic autoantibody or reliable biomarker of disease progression. Although a liver biopsy is not required for diagnosis, the characteristic histological finding is concentric periductal fibrosis resembling onion skin.PSC is associated with increased risk of several cancers, most notably, a 400 times greater risk for cholangiocarcinoma compared to the general population. Patients with PSC also face elevated risk of pancreatic and colorectal cancer. Therefore, regular screening is recommended.No drugs are currently approved for treating PSC specifically.