PART TWO
Diagnostic Cytology
Introduction
incidence of Pediatric Tumors
and Histologic types
C h ild re n are n o t sm all adults, and th e y show a distinctive
incidence, histo lo g ic typology, and b iolog ic b ehavior fo r m ost
m alignancies, w h ic h d iffe r considerably fro m those o f adults.
Pediatric tu m o rs are o fte n lin ke d to genetic aberrations o r fa m il-
ial disorders, the association between developm ental ab nor-
m alitie s and tu m o r in d u c tio n being com m on. O n the o the r
hand, fetal and neonatal m alignancies tend to d ifferentiate o r
regress spontaneously, w h ic h accounts fo r th e ir h ig h survival
and c u ra b ility rates.
It
is
d iffic u lt to
d istin g u ish
m o rp h o lo g ic a lly betw een
neop lasm o r pseudoneoplasm in c hild re n, p a rtic u la rly in
new b orns and infants. There are tw o special categories o f
pseudoneoplasm : (1 ) h ete rotyp ia o r choristom a, fo rm e d b y
n o rm a l cells/tissues in an a b n o rm a l lo c a liz a tio n (e.g. ectopic
suprarenal tissue in kidneys o r pancreatic tissue in th e gastric
w a ll), and (2 ) h a m a rto m a , w h ic h is th e excessive focal p ro -
life ra tio n o f n ative cells/tissues in an organ th a t distorts its
n o rm a l architecture (e.g. h em ang iom a, cardiac rha b d o m yom a ,
lym p h a n g io m a , and d evelop m ental cysts o f kidney, lung , o r
pancreas).1
A c om m o n neoplasm o f c h ild h o o d is teratom a, consisting o f
e m b ryonary elem ents derived fro m one, tw o, o r all three germ i-
nal layers. Som e teratom as are congenital; th ey localize prefer-
e n tia lly in the gonads, sacrococcygeal region, o r m id d le lin e o f
the b o d y (retro p erino te um , m ed iastinum , head and neck) and
have diverse b iolog ic behaviors, being in the m ature teratom a a
benign disease and in the im m a tu re teratom a a m a lig n a n t and
occasionally fatal c o n d itio n .2,3
T h e m o st fre q u e n t m alignancies o f c h ild re n o rig in a te in
th e h e m a to p o ie tic and nervous system , s o ft tissues, bone,
and kidneys. T h e ir incidence varies consid erab ly w ith in age
groups. In c h ild re n you ng e r th a n 5 years, th e m o st fre q u e n t
cancers are acute lym p h o b la s tic le u ke m ia (3 6 .1 % ), te rato m a
(1 6 .6 % ),
p o ste rio r fossa tu m o rs
(1 6 .6 % ),
n eu ro b lasto m a
(1 4 % ), W ilm s ' tu m o r (9 .7 % ), re tin o b la s to m a (6 .3 % ), hepa-
to b la sto m a (3 .1 % ), rhab d om yosarcom a (3 .1 % ), and p rim i-
tive neuroectod erm al tu m o r-E w in g 's sarcom a (P N E T -E W S o r
E W S -P N E T ) (0 .3 % ), and in those you ng e r th a n 15 years the
m o st fre q u e n t m alig nancies are leukem ias (31.5% ) and ly m -
p hom as (1 0 .7 % ).4
Techniques in Pediatric Cytopathology
Fine-needle asp iration (FN A ) techniques in pediatric tu m o rs are
s im ila r to those o f FN A in adults. O ne tro u b le w ith p e rform -
ing FN A in child ren is th e ir lack o f cooperation, especially in
d iffic u lt locations, fo r w h ic h it is necessary to includ e parents
o r relatives in the procedure. To avoid repeating the FNA, it is
im p o rta n t to im m e d ia te ly assess the sam ple sufficiency. This
evaluation m ust be m ore d em anding th a n in adults, since it is
o fte n necessary to use com p lem entary techniques to reach the
d iffe re n tia l diagnosis, as fo r m a lig n a n t ro u n d cell tu m o rs.4,5
T he diagnosis o f pediatric tu m o rs m ust always take in to
account the clinical history, p atient age, tu m o r loc aliza tio n , phys-
ical exam ination, rad iolog ic proofs, lab o rato ry tests, and special
techniques such as im m unocytochem istry, electron microscopy,
flo w cytom etry, cytogenetics, and m olecular b iolog y.5
FNA Cytology: Indications, Advantages,
Contraindications, and Complications
Fine-needle asp iration is increasingly being em ployed in the
diagnosis o f pediatric tu m o rs because o f its h ig h diagnostic
yield , rapidity, and safety. Because o f its lo w cost, it is also being
used fo r the d iffe re n tia l diagnosis between benign and m alig -
n an t lesions in the p rim a ry care u nits o f m an y underdeveloped
countries.6
indications
• The main indication is the presence of a persistent tumor
at any location or organ.4
• Detection of an unsuspected neoplasm.
• Nontraumatic confirmation of the nature of a suspected
neoplasm.
• Simple and efficient monitoring of the evolution of a
neoplasm and/or its therapeutic outcome.
Advantages and Limitations
Fine-needle asp iration cytology allow s the diagnosis to be
reached in a sim ple, fast, less invasive, less traum atic, m ore
efficient, and m ore cost-effective fa sh io n .4
T his im p lies the fo llo w in g .
• A better acceptance by children of cytologic tests instead
of biopsies.
• Capability to acquire cells out of deep locations that are
less accessible for a biopsy, such as the mediastinum and
retroperitoneum.
• Chance of repeating the test, which may be useful in
evaluating the progression or regression of a malignancy
after treatment.
• Obtaining samples from a wider area than with a biopsy.
• Better observation of cellular structures, which is impor-
tant for making the differential and specific diagnosis of
certain malignancies in children, such as malignant round
cell tumors.
• Better evaluation of the biologic nature of an inflamma-
tory response as well as detection of infectious agents.
• Chance of performing complementary diagnostic tech-
niques starting from cytologic material, such as histo-
chemistry, electron microscopy, image analysis, flow
cytometry, cytogenetics, immunocytochemistry, and
molecular probes with good performance.
C ytolog y also has lim ita tio n s .
• Interpretation of cellular morphology can be highly sub-
jective, and histopathologic criteria are not always applica-
ble to cytology.
• Cytologic diagnosis must frequently be confirmed by
histopathology.
• Cytology cannot often determine the stromal invasiveness;
the aspirated material may not represent the true nature
of the whole lesion, such as in cases in which the FNA
shows only cells from one of the components of a mixed
neoplasm such as hepatoblastoma or Wilms' tumor.
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