PART TWO
Diagnostic Cytology
and slig h tly eosinop hilic. N um erous eosinophils, lym phocytes,
and d end ritic cell-like macrophages are also present. A t an
ultrastructural level the h a llm a rk o f the Langerhans cell are cyto-
plasm ic Birbeck granules present in variable num bers and usually
having a characteristic shape (te n n is racket fo rm ). A rare variant
is Langerhans cell sarcoma, w h ic h is p leom orp hic and m o rp h o -
log ically h ig h grade and runs an aggressive clinical course.
T u m o r cells stain fo r S-100 and C D 1a and are negative fo r
a lm ost all m ature T- and B-cell m arkers, as w e ll as m ye lo id
m arkers. T he y are variab ly p ositive fo r C D 45, C D 68, and lys-
ozym e.192 FC M is o fte n nondiagnostic.
D ifferential Diagnosis
Langerhans cells are u su ally b lan d -lo oking , so th ey can be
d ifferentiated fro m lym p h om a. T he y are d ifferentiated fro m
reactive histiocytes b y th e ir characteristic cytom orp holog y, par-
tic u la rly th e ir classic nuclear grooves and the associated eosi-
n o p h ilia . D e rm atop athic lym p h ad e no p athy m ay contain m any
Langerhans cells b u t is u su ally associated w ith m elan in -la d en
macrophages.
Myeloid Sarcoma
Clinical
M ye lo id sarcom a is a tu m o r o f m yeloblasts o r im m a tu re m ye lo id
cells occurring in an extram ed ullary site o r in bone. T he tu m o r
mass m ay precede o r occur concurrently w ith acute o r chronic
m ye lo id leukem ia, o th e r types o f m ye lo p rolifera tive disorders,
o r m yelodysplastic syndrom e.1
Cytomorphology
T u m o r cells are und ifferentiated o r blastic o r show granulocytic
and som etim es m onocytic d iffe re n tia tion . The neoplastic cells
have round , irreg ularly fold ed o r lob ulated nuclei, fin e o r vesicular
chrom atin, and sm all to p ro m in e n t nucleoli. The cytoplasm is
m oderate and usually fin e ly granular. Im m a tu re eosinop hils m ay
be present and are h e lp fu l in the d ifferential diagnosis.
D ifferential Diagnosis
M ye lo id sarcom a sho uld be d ifferentiated fro m lym p h om as by
im m u n o p h e n o typ e and clinical h isto ry.193 T he m yeloblasts in
granulocytic sarcom a u su a lly e xh ib it m yeloid-associated a n ti-
gens, C D 13, C D 33, CD117, and m yeloperoxidase. The m o n o -
blastic and m on oc ytic variants are u su a lly p ositive fo r C D 68,
lysozym e, C D 14, and CD11c. M ost m ye lo id sarcomas express
C D 43, b u t n o t CD 3.
Histiocytic and Dendritic Cell Neoplasm s
These are relative ly u n c o m m o n in tum ors, representing less
th an 1% o f lym p h node neoplasm s. These includ e histiocytic
sarcomas, in te rd ig ita tin g d end ritic cell sarcomas, and fo llic u la r
d end ritic cell sarcomas. G enerally, th ey have the im m u n o p h e -
notype o f the m o th e r cell and behave as lo c a lly aggressive sarco-
mas. D iffe re n tia tio n fro m lym p h om as and m ye lo id sarcomas is
o f m a jo r clinical im p ortance.1
Prim ary and Metastatic Nonhem atopoietic Neoplasms
Lym p h nodes contain b lo o d and lym p h atic vessels as w e ll as
strom a l tissue. Therefore sarcomas in lym p h nodes can be p ri-
m ary o r m etastatic as opposed to e p ith elial neoplasm s, w h ic h
are presum ed to be m etastatic o r a result o f direct extension fro m
an adjacent carcinom a. N o nh e m a to p o ie tic neoplasm s in lym p h
nodes are identical to th e ir p rim a ry counterpart. The challenge,
Fig. 24.40 Small-cell carcinoma. Small to intermediate-sized cells
with lack of cellular cohesion may cause raise suspicion for lymphoma
(Papanicolaou x OI).
however, is th a t som etim es these neoplasm s can m im ic ly m -
phom as in aspirates.
In the pediatric p o p u la tio n , a n um b er o f n o n lym p h o re tic u -
la r neoplasm s m ay sim ula te sm all-cell lym p hom as. Ewing's
sarcom a closely resembles a sm all-cell lym p h o m a . Frequently,
a large p ro p o rtio n o f the aspirated tu m o r cells are in d iv id u a lly
dispersed. However, in te rc e llu la r cohesion in the fo rm o f sm all
to large aggregates (in c lu d in g pseudorosettes) m ay be evident.
O th e r entities th a t m im ic a sm all-cell lym p h o m a includ e neu-
rob lastom a (lo o k fo r pseudorosettes, fila m e n tou s background
m aterial, and larger neoplastic g anglion cells), W ilm s ' tu m o r
(lo o k fo r tu b ule fo rm a tio n and spindled neoplastic cells), and
rhabdom yosarcom a (lo o k fo r cellular p leo m o rp hism inc lu d in g
binucleated and m ultin u clea te d tu m o r cells). Im m u n o h is to -
chem istry w ill be very h e lp fu l in subclassification and d iffe re n -
tia tio n fro m a ly m p h o id neoplasm .
In adults, one always needs to consider the p o ssib ility o f
sm all-cell und ifferentiated carcinom a, m ost c o m m o n ly arising in
the lung, in the d iffe re n tia l diagnosis o f b o th sm all to m e d iu m -
sized lym p hom as o r LCLs (Fig. 24.40). Rarely, sm all-cell carci-
nom a m ay show a lm ost no evidence o f inte rce llula r cohesion.
Such specimens m ay require very careful searching fo r aggregates,
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