Fig. 27.63 Fine-needle aspiration retroperitoneal malignant fibrous
histiocytoma (Papanicoloau x MP).
of the thigh. Rarely, they can occur in the retroperitoneum. Alve-
olar soft part sarcomas tend to be poorly circumscribed tumors
with areas of necrosis and hemorrhage.
They are composed of large uniform epitheloid cells having
abundant granular eosinophilic cytoplasm. The tumors cells
are arranged in an alveolar pattern with thin sinuisoidol vessels
separating the solid
of tumor cells (Fig. 27.66A).
Mitotic figures are uncommon. The cells frequently con-
tain rhomboid or rod-shaped crystallia inclusions that are best
demonstrated with PAS stain after diastase digestion.
These tumors show a specific cytogenetic alteration for
(17)t(X;17)(p11;q25), resulting in the fusion of the TFE3
transcription factor with ASPL. The ASPL-TFE3 fusion pro-
tein functions as an aberrant transcription factor in the
tumor. By electron microscopy, membrane-bound or free
rhomboid crystals with a periodicity of 10 nm are noted (Fig.
Metastasis can occur early in the course of the disease to sites
such as lung, bone, and brain.
One of the most frequent indications for FNA of retroperito-
neal masses is for evaluation of lymphoma. The indications for
FNA of lymphoma in this site include establishing an initial
diagnosis of lymphoma before excisional biopsy, diagnosis
of lymphadenopathy in patients with a history of more than
one neoplasm, pathologic diagnosis in patients who are poor
candidates for excisional biopsy, evaluation of a residual or
recurrent mass after either radiation or chemotherapy, stag-
ing of lymphoma, evaluation of other lesions (neoplastic or
infectious) that may occur in the course of the disease, and
acquisition of tissue for immunologic markers. For optimal
cytologic diagnosis, morphology should be supplemented
with immunocytochemistry,154 including precise evaluation
of the proliferation index using Ki67 or MIB1 antibodies (Fig.
Contemporary standards demand that lymphomas are clas-
sified cytologically based on the WHO classification for non-
Hodgkin's and Hodgkin's lymphoma (see Table 27.12). In a
Fig. 27.64 Rhabdomyosarcoma. Small round and spindle cells, some
with eccentric nuclei set in a myxoid background. Fine-needle aspiration
(Papanicolaou x LP).
study performed at MDACC involving FNA of 238 consecutive
cases of intra-abdominal and retroperitoneal lymphoma, non-
Hodgkin's lymphoma accounted for 82% of cases, followed by
Hodgkin's lymphoma.154 Some of the pitfalls in FNA of lym-
phoma include difficulty in interpreting low- and intermedi-
ate-grade lymphomas without benefit of immunocytochemistry
studies, in which differentiation from reactive processes may be
difficult, and poor yield of cells, such as in nodular sclerosing
Hodgkin's lymphoma. Other tumors to be considered in the
differential diagnosis of lymphoma include small round blue
cell tumors (discussed earlier) and poorly differentiated carci-
noma. A detailed cytologic description of the various subtypes
of non-Hodgkin's and Hodgkin's lymphoma is given elsewhere
(see Chapter 24).
Fine-needle aspiration is frequently used in the staging of
metastatic disease and may obviate the need for exploratory
laparotomy. The most frequent carcinomas diagnosed in the
retroperitoneum are those arising in pelvic organs—namely,
the prostate, testes, urinary bladder, cervix, and endometrium.
These tumors metastasize to pelvic and para-aortic regional
lymph nodes in a sequential manner. Other primary sites that
may involve retroperitoneal nodes and may present as masses
include the ovary, kidney, adrenal, stomach, colon, pancreas,
lung, breast, and melanoma.
The diagnosis of metastatic carcinoma is usually straightfor-
ward, relying on the presence of "alien" cells, which are cells
not normally indigenous to normal lymph node constituents.
Comparing these observations with prior histologic findings
and obtaining the correct clinical history are of paramount
importance. The usual types of carcinomas involved are squa-
mous cells from the uterine cervix, vagina, and lung; adeno-
carcinoma, which may derive from the gastrointestinal tract,
prostate, uterus, ovaries, breast, and lung; and melanoma. Their
cytologic appearance is similar to that described in their primary