• Also known as neurilemoma
• Encapsulated biphasic nerve sheath tumor derived from Schwann cells with highly ordered cellular component (Antoni A) that palisades (Verocay bodies), plus myxoid component (Antoni B)
• Small tumors may be all Antoni A

• Ages 20-50; M=F
• Head, neck, flexor upper and lower extremities, retroperitoneum, posterior spinal roots, cerebellopontine angle
• Slow growing; no symptoms until becomes large; may wax and wane in size
• Pain or rapid enlargement of preexisting lesion are suggestive of malignant change
• May be due to alteration / loss of NF2 gene product

• Occurs even without neurofibromatosis, tumors usually have epithelioid features and often areas of benign schwannoma (Am J Surg Pathol 2001;25:13)
• Transforms to MPNST, angiosarcoma or epithelioid malignant change (EMC)
• Most common sites are limb, limb girdles, head/neck
• Schwannoma with MPNST: benign schwannoma with no other primary tumor that may have metastasized to schwannoma, histologically malignant cells resembling epithelioid MPNST; 5 year survival < 20%

• Excision; recurrence rare, so attempt to preserve nerve if clinically significant

• Usually solitary
• Large tumors may be cystic
• Nerve of origin present in periphery - does not penetrate substance of tumor
• Dumbbell tumor: in posterior mediastinum, originates from or extends into vertebral canal

Well circumscribed

• Biphasic: compact hypercellular Antoni A areas and myxoid hypocellular Antoni B areas
• Nuclear palisading around fibrillary process (Verocay bodies are often seen in cellular areas)
• Large irregularly spaced vessels are most prominent in Antoni B areas
• Gaping tortuous lumina have thickened hyalinized walls and may have thrombi
• Tumor cells have ill defined cytoplasm, dense chromatin
• May have foamy macrophages
• Often displays degenerative nuclear atypia (ancient change)
• Amianthoid fibers or collagenous spherules: large nodular masses of collagen with radiating edges
• Rarely epithelioid, glandular (may be entrapped sweat glands), pigmented, plexiform, rosettes
• Rare mitotic figures, no axons except where nerve is attached

Various images

• EMA (capsule), S100 (Schwann cells), calcinurin, laminin, type 4 collagen, vimentin, CD68, GFAP

• Keratin, neurofilament, desmin

• Elongated cells with continuous basal lamina, thin cytoplasmic processes, aggregates of intracytoplasmic microfibrils, peculiar intracytoplasmic lamellar bodies, extracellular long-spacing collagen
• Contains lipid
• Has characteristic luse bodies (long spaced collagen)

• Appendiceal smooth muscle
• Calcifying aponeurotic fibroma
• Fibrous histiocytoma
• Leiomyoma
• Leiomyosarcoma

• Definition: benign schwannoma with transition to angiosarcoma (irregular vasoformative structures lined by multilayered cells with nuclear atypia or atypical endothelial cells with a solid growth pattern, Am J Surg Pathol 2001;25:13, Pathol Int 2012;62:500, Cancer 2000;89:1577)
• Cytoplasmic staining for CD31, CD34 or vWF

• 73 year old man with epithelioid angiosarcoma arising in plexiform schwannoma of sciatic nerve (Hum Pathol 2007;38:1096)

Epithelioid angiosarcoma arising in a schwannoma

• Pleomorphic hyalinizing angiectatic tumor (PHAT)

• Degenerative change to tumors, usually large and of long duration, deep within retroperitoneum
• Cyst formation, calcification, hemorrhage (stromal hemosiderin), hyalinization, histiocytic infiltration, severe nuclear atypia (nuclear hyperchromasia, irregular nuclear shapes)
• No mitotic figures

• 32 year old man with hypopharyngeal tumor (Indian J Otolaryngol Head Neck Surg 2011;63:60)
• 46 year old woman with neck tumor (J Cancer Res Ther 2010;6:234)
• 53 year old woman with rapidly growing palpable mass in thigh (Br J Radiol 2010;83:e154)
• 64 year old woman with abdominal wall mass (BMC Surg 2010;10:1)

Large, hyperchromatic, multilobated nuclei

Various images

Hypopharyngeal tumour

Thigh mass mimicking malignancy

Abdominal wall mass

• Primarily Antoni A areas without Verocay bodies; usually in retroperitoneum, pelvis, mediastinum
• May have nuclear atypia and focal necrosis
• 0-3 mitotic figures/10HPF; 5% recur, no metastases

• 27 year old woman with paraspinous mass (Arq Neuropsiquiatr 2003;61:1035)
• 41 year old man with presacral tumor (Can J Surg 2002;45:141)

Site unknown

Nasal cavity

Bipolar spindle cells

S100 positive

• Large epithelioid cells with abundant eosinophilic cytoplasm, vesicular chromatin, prominent nucleoli, resembles epithelioid MPNST (Am J Surg Pathol 2001;25:13)
• May recur locally, may be a precursor lesion to MPNST since younger age than MPNST
• Strongly S100+
• Suggest sign out as "atypical schwannoma with epithelioid cells"

• First described in 2008 (Am J Surg Pathol 2008;32:1080)
• Median age 63 years, range 11-93 years
• Often arises in GI tract submucosa (Ann Diagn Pathol 2011;15:198); also other sites
• Not associated with neurofibromatosis types 1 or 2

• 61 year old man with sigmoid colon tumor (Arch Pathol Lab Med 2013;137:284)

• Median 4 cm, range 0.4 to 23 cm

• Circumscribed, unencapsulated tissue (encapsulated if in subcutis)
• Infiltrative in visceral locations
• Microcystic and reticular growth pattern with anastomosing and intersecting spindle cells, distributed around islands of myxoid or collagenous/hyalinized stroma
• Round/oval nuclei with tapering, indistinct nucleoli
• 0-3 MF/50 HPF
• No necrosis, no pleomorphism

Various images from GI tract

Colon

• S100, variable GFAP

• Muscle markers, keratin, p63

Irregular cell borders, elongated nuclei

• Pigmented tumor cells have widely scattered, coarse pigment, reactive with Fontana Masson stain (melanin stain), nonreactive with Prussian blue (iron stain)

• 55 year old man with abdominal mass (Case Rep Gastroenterol 2009;3:222)

Omental tumor

Omental tumor

• S100 (strong), vimentin, Fontana Masson

• Prussian blue, tyrosinase, HMB45 (Arch Pathol Lab Med 2002;126:816)

• 5% of schwannomas
• Pattern not strongly associated with neurofibromatosis 1 or 2
• Usually superficial, in dermis or subcutaneous tissue

• 12 year old girl with solitary superficial tumor of back (Case of the Week #50)

• Plexiform architecture with nuclear palisading
• Biphasic pattern may not be prominent
• Often cellular with hyperchromatic nuclei and mitotic activity
• No necrosis, no myxoid change

Plexiform architecture

Nuclear palisading

Cellular areas

S100

Various images

• S100 (strong staining of nodules but not intervening stroma)

• MPNST: may be multinodular, S100 weak/negative, should be sampled extensively to rule out a plexiform schwannoma (Am J Surg Pathol 2005;29:1042)
• Plexiform neurofibroma: early childhood, associated with neurofibromatosis type 1; found with grossly enlarged and tortuous nerves; hypocellular with myxoid background; no biphasic pattern; may occasionally show nuclear palisading; S100+ but only scattered cells

• Part of Carney's syndrome of functioning extra-adrenal paraganglioma, gastric epithelioid leiomyosarcoma, lung hamartoma
• Arises from spinal nerve roots
• Low grade malignancy: recurs locally, rarely metastasizes

Various images

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