Neurofibromatosis (NF) is an autosomal dominant disorder with numerous presentations that can affect nearly every organ system. The two major subtypes of NF are type 1 (NF1), also historically referred to as peripheral NF, and type 2 (NF2), which is also known as central NF. These terms are not completely accurate, however, because NF1 also can include central nervous system (CNS) abnormalities.
About 50% of cases of NF are familial; the other 50% are caused by spontaneous gene mutation. NF1, also known as von Recklinghausen disease, is a common genetic disorder involving a mutation in the gene that produces neurofibromin on chromosome 17; the condition affects one in every 3000-4000 births. All races are affected, and the two sexes are affected equally.
Two or more of the following seven criteria must be present in order to make the diagnosis of NF1:
Six or more café au lait spots (irregularly shaped, evenly pigmented, brown macules) that are greater than 5 mm in diameter in prepubertal patients or greater than 15 mm in diameter in postpubertal patients;
Two or more neurofibromas;
Axillary or inguinal freckling;
Lisch nodules (hamartomas of the iris);
Optic nerve gliomas;
Various types of osseous lesions; and
A first-degree relative with the condition.
Symptomatic NF1 typically initially manifests as café au lait spots that may be present at birth or that appear over time during childhood. Axillary or inguinal freckles are not usually present at birth, but rather appear throughout childhood and adolescence. Neurofibromas are rarely seen in young children but usually appear over time in older children, adolescents, and adults.
The patient may have as few as three or as many as thousands of these benign lesions, which consist of Schwann cells, neural fibroblasts, mast cells, and vascular elements. The neurofibromas may occur anywhere in the body and can potentially lead to marked disfigurement. If the lesions are deep, they may be detected only through palpation; cutaneous lesions may initially appear as small papules on the trunk, the extremities, the scalp, or the face.
A specific type of these lesions is a plexiform neurofibroma, which is a more diffuse type of growth that can be locally invasive and quite deep. These lesions may be associated with bony erosion and pain, and they may also be accompanied by overlying hyperpigmentation or hypertrichosis.
The onset of puberty or pregnancy may be associated with an increased number of neurofibromas, as well as an increase in the speed of preexisting lesion growth. Lesions along visual, auditory, or CNS nerve pathways may result in blindness, deafness, or neurologic deficits.
On histology, the neurofibromas are generally well-differentiated tumors that contain elongated spindle-shaped cells and pleomorphic fibroblast-like cells. Some lesions may contain inflammatory cells.
Occasionally, a large neurofibroma, a deep plexiform neurofibroma, or a peripheral nerve sheath tumor residing within the brachial or pelvic plexus may undergo malignant transformation into a neurofibrosarcoma. Unlike benign neurofibromas, neurofibrosarcomas are characteristically hypercellular, with giant cells, increased numbers of mitoses, and vascular proliferation. In addition, small masses of malignant cells may be present within larger masses of benign cells (eg, as in a plexiform neurofibroma).
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