Kidneys, Adrenals, and Retroperitoneum
T he retrop eritoneal space is m esod erm ally derived and is the
region between the p osterior layer o f the parietal p e ritoneum
and the muscles o f th e p osterior w a ll o f the ab d om in al cavity.
It extends fro m the diaphragm sup e rio rly th ro u g h to the pelvic
p eritoneal attachm ents in fe rio rly and encompasses the lu m b a r
and ilia c regions. The a n te rio r extent o f the space is lim ite d to
the p o sterior layer o f the parietal p e rito ne um and the m esentery
o f the sm all b ow el and the colon. The m a jo r structures w ith in
th is include the a b d om in al aorta, in fe rio r vena cava, kidneys,
ureters, adrenal glands, sym pathetic trunks, and celiac and sacral
plexus o f nerves. The space is fille d w ith fib rous tissue, fat, fascia,
loose areolar connective tissue, b lo o d and lym p h a tic vessels and
lym p h nodes, and nerves.155
A p rim a ry retrop eritoneal tu m o r is generally considered to
be one th a t originates ind ep end ently w ith in the re tro p e rito -
neal space w ith o u t p rim a ry anatom ic connection to any o f the
retrop eritoneal organs.156 Tum ors o f the retro p e rito ne um m ay
be b roa d ly classified as being o f m esoderm al o r neurogenous
o rig in, as arising fro m tissue rem nants and heterotop ic tissue,
o r as in v o lv in g lym p h nodes, b o th p rim a ry lym p h om as and
metastases (Table 27.10).20
Neoplastic Lesions
It is beyond the scope o f th is chapter to detail the m u ltitu d e
o f tu m o rs in the retro p e rito ne um . Som e are extrem ely rare and
have n o t been described by FNA.
Benign Tumors and Masses
Experience w ith FNAs fro m these sites is lim ite d b u t growing. FN A
o f a retrop eritoneal cystic schw annom a dem onstrated num erous
single spindle-shaped cells w ith th in , w avy cytoplasm and cigar-
shaped nuclei.157 The presence o f isolated cells and clusters o f
Schwann cells arranged in an organoid pattern o f Verocay b od -
ies is characteristic o f schwannom a. Deep-seated retrop eritoneal
lip om as are rare, and in fact, d istin c tio n o f large lip om as o f the
Table 27.9 Cytologic Diagnosis of 558Retroperitoneal Masses
by Fine-needle Aspiration Performed at the M.D. Anderson
Cancer Center (1968-1993)
Metastatic carcinoma (cervix, endometrium,
ovary, prostate, bladder)
Germ cell tumor
Other neoplasms (melanoma, ovarian
stromal tumor)
Miscellaneous non-neoplastic lesions
(inflammatory, cyst, lymphocele)
Negative for malignancy
Inadequate or nondiagnostic
retro p e rito ne um fro m w e ll-d iffere ntia te d liposarcom as m ay be
exceedingly d ifficu lt. It is lik e ly th a t m ost o f the huge retro p e rito -
neal lip om as p reviously described represent w e ll-d ifferentiated
liposarcom as. O th e r m iscellaneous benign cond itions th a t can
be diagnosed b y FN A include abscesses, cysts, hem atom as, and
infectious g ranulom atous processes such as tuberculom a.
Retroperitoneal Sarcomas
R etroperitoneal sarcomas com pose 13% o f a ll sarcomas.157
The m ost c om m o n sarcomas reported in th is site are liposar-
coma, leiom yosarcom a, fibrosarcom a, M FH , neurogenic sarco-
mas, and o th e r unclassified sarcomas. Preoperative diagnosis
b y FN A o f soft tissue lesions m ay be o f value in preoperative
evaluation o f patients and in the choice o f op eration; however,
sam p ling m ay be a p roblem , as in the diagnosis o f a d ediffer-
entiated c om p onent o f a large, p re d o m in a n tly low -grade re tro -
p eritoneal mass such as a w e ll-d iffere ntia te d liposarcom a. This
p rob lem could p o te n tia lly be overcom e b y jud icious sam pling
o f suspicious inhom og eneous areas detected b y CT scan. U n til
m ore experience is accum ulated, d e fin itive classification should
be based on the surgical resection. Reports o f the accuracy o f
cytology in retrop eritoneal sarcomas are lim ite d to a fe w cases
o r single case reports. D N A image analysis on a dedicated Feul-
gen-stained sm ear (Feulgen stain can also be p erform ed on a
destained Papanicolaou sm ear) can be o f assistance in help ing
to grade soft tissue sarcomas. In general, low-grade sarcomas are
d ip lo id w ith lo w p ro life ra tio n , whereas high-grade sarcomas
are aneup loid o r te trap lo id w ith elevated p ro life ra tio n and cells
w ith D N A content exceeding 5C.
The retro p e rito ne um is the second m ost c om m o n lo c a tio n fo r
liposarcom a, w h ic h m ay reach very large p rop ortions. Because
o f the d iffic u lty in com p letely excising these tum ors, the rate
o f local recurrence is high. O w ing to local com pression effects,
massive recurrence m ay be fatal. The A rm ed Forces In stitu te
o f P atholog y classification divides liposarcom a in to fo u r cate-
gories: (1) m yxo id liposarcom a, (2 ) ro u n d cell liposarcom a,
(3) w e ll-d iffere ntia te d liposarcom a, and (4 ) p leo m o rp hic lip o -
sarcom a (see Fig. 27.62A -D ).
M yxo id liposarcom a is the m ost c om m o n type o f liposarcom a
and is characterized h isto lo g ic a lly b y p ro life ra tin g lipoblasts
in various stages o f d iffe re n tia tio n , a delicate p le xifo rm capil-
la ry pattern, and a m yxo id m atrix. O n cytology, the tu m o r cells
appear sm all and u n ifo rm w ith in d istin c t cytoplasm ic borders.
The m yxo id background, w h ic h stains m etachrom atically blue-
red w ith D iff-Q u ik stain, contains num erous delicate p lexiform
capillaries com posed o f sm a ll branching aggregates o f end othe-
lia l cells. A few sm all, m ultiva cu ola ted lip ob lasts m ay be fo u n d
and are characterized b y an eccentric scalloped hyp erchrom atic
nucleus w ith surro un d in g fa t vacuoles (Fig. 2 7.6 2 D ).158
R ound cell liposarcom as are closely related to m yxoid lip o -
sarcomas and tend to be m ore aggressive.159 Cytologic study
reveals excessive num bers o f u n ifo rm sm all ro u n d cells w ith
vesicular nuclei. These m ay be confused w ith o the r sm all rou nd
cell neoplasms. The presence o f an occasional vacuolated lip o b -
last as w e ll as ultrastructural exam ination fo r lip id confirm s the
W e ll-d iffere ntia te d liposarcom as closely sim ula te lip om as
h isto lo g ic a lly except fo r the presence o f a few lipoblasts, o r
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