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RESIDENT
CASE
STUDIES
Week 5 May 19 - May 23, 2003: Case
4
Table
of Contents | List of Diagnoses | Case 1 | Case 2
| Case
3 | Case 4
One
year old male with abdominal mass
Discussion:
The histologic findings of
this case should remind you of the “small round blue cell” tumors,
which in children include: rhabdomyosarcoma, lymphoma/leukemia, Ewings
sarcoma/PNET, medulloblastoma, neuroblastoma, desmoplastic small round
blue cell tumor. It is sometimes difficult to differentiate between these tumors
without the use of immunohistochemistry and/or molecular pathology
techniques. All these should feature in the differential diagnosis.
The
diagnosis for the above case is Neuroblastoma. Most cases are diagnosed by
the age of 4 years. The median age at diagnosis is 21 months. It
is extremely rare in adults. The tumor commonly develops in
relationship with the sympathetic nervous system and most often appears as
an abdominal mass. Neuroblastoma is twice as likely to occur in the
adrenal gland as opposed to the extra-adrenal primary sites (head and neck
region, mediastinum or pelvic area). About 80 to 90% of
neuroblastomas have elevated catecholamines (norepinephrine,
epinephrine) and their metabolites [homovallinic acid (HVA),
vanillymandelic acid (VMA), and 3-methoxy-4-hydroxyphenylglycol (MHPG)] in
their urine. Measurements of these catecholamines and their metabolites
can be used to monitor the course of the disease during therapy. High VMA/HVA ratios have been associated with good prognosis (ratios 1.5
or more).
On
microscopic examinations, neuroblastomas are composed of sheets of small
round blue cells (collection of small cells with hyperchromatic nuclei and
scant cytoplasm). There may be vague lobulation owing to thin
fibrovascular septa between groups of tumor cells. A finely fibrillar
eosinophilic matrix (schwannian / neuropil) is found between the tumor
cells, which at ultrastructural level, corresponds to masses of
unmyelinated axons. Schwannian /neuropil
stroma, when present, differentiates neuroblastoma from other small
round blue cell tumors, even without special stains or molecular
pathology. No other small round blue cell tumors of non-neural origin has
schwannian stroma (Dr. K Atkins, verbal). The schwannian stroma in itself is of no prognostic significance,
but it can help differentiate the tumors into “stroma rich” and
“stroma poor”. Homer Wright pseudorosettes
(one or two layers of neuroblasts arranged around a central space
that is filled with tangles of neuritic processes) are found in about 30%
of the cases. Immunohistochemically, neuron specific enolase is present in
virtually all cases of neuroblastoma, but this can be present in non
neuroblastic tumors. S100 protein is strongly expressed
in the ganglioneuromatous portions of these tumors and may correspond to
the degree of differentiation. CD99 is usually negative.
The
major differential diagnosis in this case is Wilm’s tumor (nephroblastoma),
which occurs in the same age group in the kidney. Wilm’s tumor is
usually triphasic and not monophasic as in neuroblastoma. Predominance of
small round blue cell may be present in Wilm’s tumor (blastema),
however, this is rare. The blastemal component of Wilm's tumor (WT) might
be indistinguishable histologically from other small, blue, round-cell
tumors of childhood, including alveolar rhabdomyosarcoma (RMS),
particularly in small biopsy specimens and in the setting of metastatic
disease. Use
of immunohistochemistry and cytogenetics might be of value.
For
prognostic indicators of neuroblastoma, see Week 4 case2
discussion.
References:
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Verbal
communication – Dr Kristen A. Atkins.
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Diagnostic surgical pathology / editor, Stephen S. Stenberg – 3rd
edition.
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Weiss, Sharon W. Enzinger and Weiss’s soft tissue tuimors /
Sharon W. Weiss, John R. Goldblum – 4th edition.
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