Nuchal-type

fibroma Fibromas are benign tumors that are composed of fibrous or connective tissue. They can grow in all organs, arising from mesenchyme tissue. The term "fibroblastic" or "fibromatous" is used to describe tumors of the fibrous connective tissue. Whe ...

is a rare benign proliferation involving the

dermis The dermis or corium is a layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. It is divided i ...

and subcutaneous tissues, that is a collection of dense, hypocellular bundles of

collagen Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole ...

with entrapped

adipocytes Adipocytes, also known as lipocytes and fat cells, are the cells that primarily compose adipose tissue, specialized in storing energy as fat. Adipocytes are derived from mesenchymal stem cells which give rise to adipocytes through adipogenesis. I ...

and increased numbers of small

nerves A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...

. 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 Fibroblastic and myofibroblastic tumors (FMTs) develop from the mesenchymal stem cells which differentiate into fibroblasts (the most common cell type in connective tissue) and/or the myocytes/myoblasts that differentiate into muscle cells. FMTs ...

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 The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...

(hence the name "nuchal-type"), but it can be seen in the extremities,

lumbosacral The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordates ...

area,

buttocks The buttocks (singular: buttock) are two rounded portions of the exterior anatomy of most mammals, located on the posterior of the pelvic region. In humans, the buttocks are located between the lower back and the perineum. They are composed ...

, and face. There is a strong association with diabetes mellitus and

Gardner syndrome Gardner's syndrome (also known as Gardner syndrome, familial polyposis of the colon, or familial colorectal polyposis) is a subtype of familial adenomatous polyposis (FAP). Gardner syndrome is an autosomal dominant form of polyposis characterize ...

; 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. NuchalFibroma

Immunohistochemistry

The tumor cells are strongly positive for

vimentin Vimentin is a structural protein that in humans is encoded by the ''VIM'' gene. Its name comes from the Latin ''vimentum'' which refers to an array of flexible rods. Vimentin is a type III intermediate filament (IF) protein that is expressed ...

, CD34, and sometimes with CD99. There is often (up to 2/3rds) a nuclear reaction with

β-catenin Catenin beta-1, also known as beta-catenin (β-catenin), is a protein that in humans is encoded by the ''CTNNB1'' gene. Beta-catenin is a dual function protein, involved in regulation and coordination of cell–cell adhesion and gene transcriptio ...

Diagnosis

Differential diagnoses

The differential diagnosis includes elastofibroma, fibrolipoma, desmoid-type fibromatoses, and nuchal fibrocartilaginous pseudotumor.

Management

Simple excision is curative. However, in patients with Gardner syndrome, up to 45% will develop desmoid-type fibromatosis at other sites, and so this should be searched for and excluded. Patients can develop a recurrence, so follow-up is required.

Epidemiology

This is a rare tumor, presenting over a wide age range, but usually in the 3rd to 5th decades of life. There is a slight male predilection, although this is not seen in syndrome associated patients. The most common site is the posterior neck, but may also be seen in other sites (extremities, lumbosacral area, buttocks, face).