26
Mediastinum
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Fig. 26.19 Neurilemmoma. (A) Loose fascicles of spindle cells associated with fibrillary matrix in the background are noted. Direct smear of fine-needle
aspirate (Papanicolaou x MP). (B) The spindle cells are mitotically inactive and contain occasional pseudonuclear cytoplasmic inclusions (arrow). Some of the
tumor cell nuclei have a "fishhook” appearance. Direct smear of fine-needle aspirate (Papanicolaou x HP). (C) Spindle cells with focal nuclear palisading are
identified, against a background of eosinophilic fibrillary matrix (left). The tumor cells show nuclear staining for S-100 protein, confirming the presence of nerve
sheath differentiation (right). Cell block sections of fine-needle aspirate (H&E and immunostain for S-100 protein; x LP and MP, respectively).
(Fig. 2 6.2 0A ).73,116 T he relative p ro p o rtio n o f e ith e r c om p on en t
varies. T he sm a ll ro u n d cells show a h ig h nuclear-to-cytoplas-
m ic ra tio and con tain h yp erchrom atic nuclei and som etim es
sm a ll n uc le oli. T h e y are arranged in lo o se ly cohesive clusters o r
iso la tio n . N uclear m o ld in g is n o t u n c o m m o n . H o m e r-W rig h t
rosettes and calcified m ate ria l are occasionally seen in cyto-
logic preparations. H o m e r-W rig h t rosettes appear as acinar
groupings o f tu m o r cells surro u n d in g delicate fib rilla ry sub-
stance in th e center. W h e n d ifferentiated , th e p rim itiv e n eu ro b -
lasto m a cells m ay resem ble plasm a cells, w ith eccentric nuclei
associated w ith som e b a so p h ilic cytoplasm (an early sign o f
g ang lionic m a tu ra tio n ). M o n o n u c le a r o r b inucleated g ang lion
cells can be id e n tifie d in fine-needle aspirates o f g ang lio-
neurob lastom a.
T he neurogenic nature o f tu m o r cells can be confirm ed w ith
im m un oc yto ch em ic al study fo r n eu ro n al m arkers (e.g. n eu ro -
fila m e n t and synaptophysin). T he fib rilla ry m aterial m ay be
p ositive fo r S-100 p rotein. U n lik e extraskeletal Ewing's sarcoma
o r p rim itiv e neuroectoderm al tu m o r, neurob lastom a cells are
negative fo r C D 99 (M IC 2 ). However, it is n o t possible to d istin -
guish between neurob lastom a and Ewing's sarc om a/p rim itive
neuroectoderm al tu m o r o n the basis o f m orp h olog ic exam ina-
tio n alone. M oreover, histo lo g ic classification o f neurob lastom a
cannot be applied d irectly to fine-needle asp iration cytology.
D etailed subtyping requires histo lo g ic e xa m in ation o f the
excisional specimens (Fig. 26.20B ).
As
fo r g ang lioneurom a,
the
cytologic
preparations
are
in fo rm a tiv e i f b o th n eurom atous sp ind le cells and g anglion
cells are present.73 In cytologic preparations, gang lion cells
appear as large p olyg onal cells c on tain in g ab und ant basop hilic
cytoplasm , eccentric nuclei, and p ro m in e n t s o lita ry centrally
located nuc le oli. The y are o fte n c om p letely detached fro m the
neurom atous sp ind le cell aggregates. The absence o f im m a tu re
cells, necrosis, and in fla m m a tio n differentiates g ang lioneurom a
797
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