29
Pediatric Tumors
Fine-needle aspirates shows numerous small, uniform round
or oval cells, isolated or in clusters and with nuclear molding.
Nuclei are hyperchromatic with smudge chromatin and scarce
cytoplasm. Occasionally, cells can form rosettes. Differential
diagnosis with other malignant round cell tumors must be
made with immunocytochemistry, especially with medullo-
blastoma and neuroblastoma.
Key features of retinoblastoma
• N u m e ro u s s m a ll u n ifo rm ro u n d cells;
• N u c le a r m o ld in g ; and
• O ccasional rosettes.
Tumors of the orbit
Tumors of the orbit comprise rhabdomyosarcomas (especially
the embryonary type), lymphomas, eosinophilic granuloma,
hemangiomas, PNET (FNA is described in the respective sec-
tion), optic nerve gliomas, meningiomas, metastasis of leuke-
mias, and neuroblastomas. Pseudotumoral lesions and dermoid
cysts can also occur. Lacrimal gland tumors are very rare.
inflammatory Pseudotumor of the orbit
Inflammatory pseudotumor of the orbit includes a heteroge-
neous group of tumors. Their microscopic appearance varies
in each particular case, comprising inflammatory elements,
fibrosis, and vascular proliferation in variable amounts. Fine-
needle aspirates frequently show nonspecific inflammatory
elements.
Thyroid Gland Tumors
To obtain good results in FNA of thyroid nodules, it is recom-
mended to use ultrasonography as a guide, which is essential
in lesions of< 2 cm. It is also important to include FNA of
thyroid nodules within the clinical therapeutic management
algorithms.
The histologic types of thyroid tumor in the pediatric popula-
tion and their relative frequencies are similar to those of tumors
in adults. The thyroid gland represents the most frequent source
of primary carcinomas in children, of which the papillary sub-
type is the most common.5-10
Benign tumors
Nodular Follicular Hyperplasia
Nodular follicular hyperplasia is the most frequent cause of
thyroid nodules overall, and it can be sporadic or endemic.
Nodules can be single or multiple, and they are usually non-
functional.
It is often difficult to distinguish histologically between
follicular adenoma and nodular follicular hyperplasia. Ade-
nomas have a fibrous capsule, which is absent in hyperplas-
tic lesions. It can be very hard and sometimes impossible
to make the differential diagnosis between nodular follicu-
lar colloid hyperplasia and follicular adenoma based solely
on FNA (Fig. 29.2A).11
For the key features of nodular follicular hyperplasia, see
Chapter 23
(Thyroid).
Malignant tumors
Papillary Carcinom a
Papillary carcinoma is the most frequent thyroid malignancy in
children, mostly affecting girls between 13 and 16 years without
known risk factors (60-70% of cases). Irradiation is one of the
most important pathogenic elements. Papillary carcinoma can
arise as a single or multifocal solid or cystic tumor, and it is mostly
papillary in shape. When solid, it is usually well delimited with
or without a capsule and is occasionally infiltrating or sclerosing.
Microscopically, the classic and most frequent pattern shows papil-
lae, but carcinomas can also be follicular, usually associated with
psammoma bodies and squamous metaplasia (Fig. 29.2B).10
Fine-needle aspirates in papillary carcinoma usually show
plenty of cells and scarce or absent dense colloid. Tumor cells are
cuboid to columnar in shape and larger than follicular cells, with
polygonal edges, well-defined cytoplasm, and central nuclei. The
nuclei are oval or angled with scarce pleomorphism, slight gran-
ular chromatin, nonprominent nucleoli, and frequently folds or
cytoplasmic pseudoinclusions. Cells are often arranged in papil-
lary, pseudopapillary structures and irregular sheets. The follicu-
lar variant keeps the nuclear features of neoplastic cells, which
allows it to be distinguished from follicular carcinoma.11
For the key features of papillary carcinoma, see Chapter 23
(Thyroid).
M edullary Carcinoma
Medullary carcinomas are infrequent in children and mostly
sporadic. Some medullary carcinomas are familial with or with-
out additional multiple endocrine neoplasia (MEN) type 2a or
2b syndrome defects. Sporadic medullary carcinomas often form
clinically palpable nodules without C-cell hyperplasia, while
MEN 2a and 2b syndrome-associated medullary tumors are
mostly small and multifocal with diffuse hyperplasia of C cells.
Macroscopically, medullary carcinomas can be circumscribed
or infiltrating, with a gray-white to yellow appearance and a size
ranging from 0.1 to 4-5 cm.
Microscopically, medullary carcinomas show diverse patterns:
solid, lobular, trabecular, or insular. Tumors of > 2 cm usually show
an amyloid stroma. Cells can be round, spindle, and small, with
round or oval nuclei and eosinophilic or occasionally granular
cytoplasm (Fig. 29.2C).10 Fine-needle aspirates are generally hemor-
rhagic, with abundant cells arranged in an isolated fashion and/or
in three-dimensional aggregates that rarely form follicles or papil-
lae. It is also common to find marked cellular pleomorphism, with
huge, round, spindle, or plasmocytoid cells with eosinophilic, pale,
and occasionally granular cytoplasm, or metachromatic red gran-
ules with Giemsa stain. Nuclei are often oval and slightly pleomor-
phic, with granular thick chromatin and one or two small nucleoli.
The eccentric location of the nuclei gives the cells a plasmocytoid
appearance, and cytoplasmic nuclear pseudoinclusions are rare
(Fig. 29.2D).11
Medullary carcinoma is almost always immunore-
active for calcitonin and sometimes for carcinoembryonic antigen
(CEA), which is considered as a poor prognostic factor.
For the key features of medullary carcinoma, see Chapter 23
(Thyroid).
Cervical-Thyroid Teratoma
Cervical-thyroid teratomas are relatively frequent in children
(3% of all thyroid tumors) and almost always congenital.
They affect males and females equally and are usually large,
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