AJR 2004; 183:1835-1837
© American Roentgen Ray Society
Primary Posterior Mediastinal Seminoma
James G. Ravenel1,
Leonie L. Gordon1,
Mark I. Block2 and
Uzair Chaudhary3
1 Department of Radiology, Medical University of South Carolina, Box 250322, 169
Ashley Ave., Charleston, SC 29425.
2 Department of Surgery, Medical University of South Carolina, Charleston,
SC.
3 Department of Hematology/Oncology, Medical University of South Carolina,
Charleston, SC.
Received December 16, 2003;
accepted after revision February 4, 2004.
Address correspondence to J. G. Ravenel
(ravenejg{at}musc.edu).
Introduction
Primary mediastinal germ cell tumors are rare lesions accounting for only
10–15% of mediastinal masses. Most of these tumors are benign lesions;
however, up to one third may be malignant, and seminoma is the most common
histologic subtype. Most of these tumors arise in the anterior mediastinum,
although rarely these lesions may be centered in other locations. We report a
case of a primary mediastinal seminoma arising within the posterior
mediastinum.
Case Report
A 47-year-old man sought medical attention for pain in the left side of his
chest over the past 4 months. Although the pain began intermittently, it
gradually became more constant and was accompanied by progressive dyspnea,
dysphagia, and a 25-lb (11-kg) weight loss. The patient had been in good
health leading up to this illness but did have several congenital anomalies,
including a bicuspid aortic valve, undescended left testicle at birth, and
delayed-onset puberty. The left testicle descended spontaneously when he was 4
years old. Physical examination of the scrotum revealed testes of normal size
without a palpable mass. Chest radiography revealed a large mediastinal mass.
Radiography was followed by contrast-enhanced CT that revealed a large
posterior mediastinal mass crossing into the middle mediastinum, enveloping
the descending thoracic aorta and esophagus, and externally compressing the
left main bronchus (Figs. 1A
and 1B). A large celiac lymph
node was also present, but no evidence of retroperitoneal lymphadenopathy was
seen. PET showed marked uptake in the mediastinal mass and celiac node
(Fig. 1C). No other sites of
abnormal uptake were present. Fine-needle aspirates and core biopsies yielded
a poorly differentiated neoplasm. Blood tests for germ cell tumor markers
showed a normal 
-fetoprotein level (5.3 ng/mL; normal, 0–20
ng/mL) and an elevated ß-HCG level (21 mIU/mL; normal, 0–4 mIU/mL).
Because of a suspicion of germ cell neoplasm, thoracoscopy was ultimately
performed to obtain sufficient tissue, and a diagnosis of seminoma was
made.
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Fig. 1A. —Posterior mediastinal seminoma in 47-year-old man.
Contrast-enhanced CT scan obtained at level of carina reveals large posterior
mediastinal mass pushing descending aorta anteriorly and compressing left main
bronchus. Note growth into neural foramen (arrow).
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Fig. 1B. —Posterior mediastinal seminoma in 47-year-old man.
Contrast-enhanced CT scan obtained below carina reveals complete encasement of
aorta (A) as well as mass effect on crossing right pulmonary artery and more
distal left main bronchus.
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After the diagnosis, testicular sonography was performed to look for an
occult primary tumor. The testicles were normally positioned and symmetric in
size and echogenicity, with two punctate calcifications in the right testicle.
No mass was present. Given the association with Klinefelter's syndrome and the
history of congenital anomalies, genetic karyotyping was performed and
revealed a normal XY karyotype. The patient was treated with four cycles of
etoposide and cis-platinum with a marked decrease in the size of the mass
within the mediastinum and celiac lymph node and normalization of the
ß-HCG level. Eight months after chemotherapy, the patient remained
symptom- and tumor-free.
Discussion
During embryogenesis, the primitive germ cells descend along the midline
from the yolk sac endoderm to the gonads. The prevailing theory is that
mediastinal germ cell tumors arise from multipotent germ cells that have
become "misplaced" or arrested in their migration, most often near
the thymus [1]. However, others
have suggested that these cells may be deposited in the thymus gland
[2] or originate from myoid
cells within the thymus [3].
Regardless of origin, these cells retain the ability to proliferate and
differentiate into embryonic or extraembryonic tissue. In the largest series
to date [4], all mediastinal
seminomas were said to arise within the anterior mediastinum.
Histologically, mediastinal seminomas are almost indistinguishable from
seminomas arising in the testes. In most cases, because of the propensity of
testicular seminomas to disseminate via lymphatics, studies are performed to
exclude a testicular primary. However, remnant thymic tissue may be present in
more than 25% of cases, and subtle immunohistochemical differences exist
between mediastinal seminomas and their testicular counterparts
[4]. These tumors are
considered to be primary mediastinal tumors rather than metastases from an
occult or burned out testicular primary tumor.
An increased incidence of testicular cancer exists in undescended testes.
Germ cell neoplasms develop in 5–20% of undescended testes, and the risk
is higher for abdominal testes than for inguinal testes
[5]. However, if the testis is
placed in the scrotum by orchiopexy or spontaneous migration by the age of 6
years, the risk of malignancy is very low. In our patient, the left testicle
descended spontaneously at the age of 4 years, and neither physical
examination nor sonography revealed evidence of a primary lesion.
Seminoma is the most frequent histologic subtype of malignant germ cell
tumor, accounting for 40–65% of cases
[6,
7]. These tumors typically
occur in men from the second to fourth decades of life and may present as
asymptomatic, incidentally discovered lesions in 20–30% of patients
[1]. More frequently, these
tumors cause symptoms because of the size and compression of adjacent
structures, including the trachea and superior vena cava. The most common
reported symptoms include chest pain, dyspnea, cough, and weight loss
[3,
8]. Occasionally, serum HCG is
elevated in seminoma [1,
8]. Metastatic disease occurs
in fewer than half the cases; when it does occur, it is usually spread to
adjacent lymph node groups in the neck, mediastinum, or abdomen. Hematogenous
metastases are unusual but may be seen in lung, liver, and bone
[8]. The prognosis for pure
seminomas in the mediastinum is excellent, with a 5-year survival rate of more
than 90%, with appropriate therapy.
On CT, mediastinal seminomas present as bulky, lobular anterior mediastinal
masses that may encase or invade local structures
[1]. In this regard, the
imaging findings of our patient are similar to findings of seminomas in other
locations. Calcification is distinctly unusual, but regions of cyst formation
or cystic degeneration may be present. PET is usually not performed for
staging germ cell neoplasms but was performed in this case because of the
suspicion of lymphoma and was helpful in confirming spread to the large celiac
lymph node.
Because of the tumor's location, a germ cell neoplasm was not our primary
consideration. Our initial working diagnosis included lymphoma and a
neurogenic tumor; the former was thought to be the likely diagnosis. Given the
size and extensive nature of the mass, a schwannoma or neurofibroma seemed
unlikely despite its growth into a single neural foramina. Ganglioneuroma was
also considered but would be distinctly unusual at our patient's age.
Although other germ cell neoplasms have been described in the posterior
mediastinum (mature teratomas, in particular)
[1], to our knowledge, a
primary posterior mediastinal seminoma has been described only once previously
[9]. In this case, the
individual was older than our patient, but the mass had a similar imaging
appearance, with a confluent posterior mediastinal mass encasing the
aorta.
It is not clear why a posterior mediastinal seminoma is so rare. If one
accepts the theory of cells deposited along the migratory pathway, the
posterior mediastinum should be involved more frequently as an intermediate
point between the anterior mediastinum and the retroperitoneum. In a study of
104 patients, 50% of extragonadal seminomas arose within the retroperitoneum
and 49% arose within the mediastinum
[8]. Regardless, the response
to chemotherapy of our tumor was similar to that of seminomas in other
extragonadal locations.
In conclusion, despite the classic teaching that mediastinal seminomas
arise solely in the anterior mediastinum, seminomas may originate in the
posterior mediastinum. In patients in whom histopathologic examination of
biopsy specimens from a posterior mediastinal mass is confusing, mediastinal
germ cell tumor should be considered, and appropriate laboratory and
immunohistochemical analysis should be performed.
References
- Rosada-de-Christenson ML, Templeton PA, Moran CA. Mediastinal germ
cell tumors: radiologic and pathologic correlation.
RadioGraphics1992; 12:1013
–1030[Abstract]
- Friedman NB. The comparative morphogenesis of extragenital and
gonadal teratoid tumors. Cancer1951; 4:265
–276[Medline]
- Rosai J, Parkash V, Reuter VE. On the origin of mediastinal germ
cell tumors in males. Int J Surg Pathol1995; 2:73
–78
- Moran CA, Suster S, Przygodzki RM, Koss MN. Primary germ cell
tumors of the mediastinum: mediastinal seminomas—a clinicopathologic and
immunohistochemical study of 120 cases. Cancer1997; 80:691
–698[Medline]
- Batata MA, Chu FC, Hilaris BS, Whitmore WF, Golbey RB. Testicular
cancer in cryptorchids. Cancer1982; 49:1023
–1030[Medline]
- Nichols CR. Mediastinal germ cell tumors: clinical features and
biologic correlates. Chest1991; 99:472
–479[Free Full Text]
- Moran CA, Suster S. Primary germ cell tumors of the mediastinum. I.
Analysis of 322 cases with special emphasis on teratomatous lesions and a
proposal for histopathologic classification and clinical staging.
Cancer 1997;80:681
–690[Medline]
- Bokemeyer C, Droz JP, Horwich A, et al. Extragonadal seminoma: an
international multicenter analysis of prognostic factors and long term
treatment outcome. Cancer2001; 91:1394
–1401[Medline]
- Makiyama K, Senga Y. Primary seminoma in the posterior mediastinum.
J Urol 2001;165:908[Medline]
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Introduction
Case Report
