Page 822 - Robbins Basic Pathology by Vinay Kumar, Abul K. Abbas, Jon C. Aster
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808 C H A P T E R 21 Peripheral Nerves and Muscles Traumatic Neuroma
MORPHOLOGY Traumatic neuroma is a non-neoplastic proliferation asso-
ciated with previous injury of a peripheral nerve. Injuries
Unlike schwannomas, neurofibromas are not encapsulated. that lead to the transection of axons activate a regenerative
They may appear circumscribed, as in localized cutaneous program (see Fig. 21–1) characterized by sprouting and
neurofibromas, or exhibit a diffuse infiltrative growth elongation of processes from the proximal axonal stump.
pattern. Also in contrast with schwannomas, the neoplastic With severe injuries that disrupt the perineurial sheath,
Schwann cells in neurofibroma are admixed with other cell these new processes may “miss” their target, the distal end
types, including mast cells, fibroblast-like cells and perineurial- of the transected nerve. The misguided elongating axonal
like cells. As a result, the cellular growth pattern of neurofi- processes can induce a reactive proliferation of Schwann
bromas is more haphazard than that of schwannomas. The cells, leading to the formation of a painful localized nodule
background stroma often contains loose wavy collagen that consists of a haphazard mixture of axons, Schwann
bundles but also can be myxoid or contain dense collagen cells, and connective tissue.
(Fig. 21–7, D). Plexiform neurofibromas involve multiple
fascicles of individual affected nerves (Fig. 21–7, C). Residual S U M M A RY
axons are found embedded within the diffuse neoplastic Peripheral Nerve Sheath Tumors
Schwann cell proliferation, which expand the fascicles while
leaving the perineurium intact. Diffuse neurofibromas • In most peripheral nerve sheath tumors, the neoplastic
show an extensive infiltrative pattern of growth within the cells show evidence of Schwann cell differentiation.
dermis and subcutis of the skin.
• Peripheral nerve sheath tumors are important features of
Malignant Peripheral Nerve Sheath Tumors the familial tumor syndromes neurofibromatosis type 1
(NF1) and type 2 (NF2).
Malignant peripheral nerve sheath tumors are neoplasms
seen in adults that typically show evidence of Schwann cell • Schwannomas and neurofibromas are benign nerve sheath
derivation and sometimes a clear origin from a peripheral tumors.
nerve. They may arise from transformation of a neurofi-
broma, usually of the plexiform type. About one half of • Schwannomas are circumscribed, usually encapsulated
such tumors arise in patients with NF1, and 3% to 10% of tumors that abut the nerve of origin and are a feature of
all patients with NF1 develop a malignant peripheral nerve NF2.
sheath tumor during their lifetime.
• Neurofibromas may manifest as a sporadic subcutaneous
MORPHOLOGY nodule, as a large, poorly defined soft tissue lesion, or as
a growth within a nerve. Neurofibromas are associated
Malignant peripheral nerve sheath tumors manifest as large, with NF1.
poorly defined soft tissue masses. On histologic examination,
these tumors are highly cellular and exhibit features of overt • About 50% of malignant peripheral nerve sheath tumors
malignancy, including anaplasia, necrosis, infiltrative growth occur de novo in otherwise normal persons, while the
pattern, pleomorphism, and high proliferative activity. The remainder arise from the malignant transformation of a
low-power view often shows alternating areas of high and preexisting NF1-associated neurofibroma.
low cellularity that result in an appearance described as
“marble-like.” Also frequently seen are perivascular areas of BIBLIOGRAPHY
increased cellular density.
Amato AA, Barohn RJ: Evaluation and treatment of inflammatory
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NF1 is an autosomal dominant disorder caused by muta- tures and therapy.]
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include neurofibromas of all three main types, malignant [Discussion of current concepts on the pathophysiology of idiopathic
peripheral nerve sheath tumors, optic gliomas, and other inflammatory myopathies.]
glial tumors. In addition, patients with NF1 exhibit learn-
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[Review focused on the pathologic features of inflammatory myopathies.]
