DOI:10.2214/AJR.04.1688
AJR 2006; 186:1125-1132
© American Roentgen Ray Society
Radiologic Findings of Peripheral Primitive Neuroectodermal Tumor Arising in the Retroperitoneum
Mi Sung Kim1,
Bohyun Kim2,
Chan Sup Park1,
Soon Young Song1,
Eun Ja Lee1,
Noh Hyuck Park1,
Hye-Seong Kim2,
Seung Hyup Kim3 and
Kyoung Sik Cho4
1 Department of Radiology, Myongji Hospital, Kwandong University College of
Medicine, 697-24 Hwajung-dong, Duckyang-gu, Koyang, Kyunggi 412-270, South
Korea.
2 Department of Radiology, Samsung Medical Center, Sungkyunkwan University
School of Medicine, 50 Ilwon-dong, Kangnam-ku, Seoul 135-710, South
Korea.
3 Department of Radiology, Seoul National University Hospital, Seoul National
University College of Medicine, 28 Yongon-dong, Chongno-gu, Seoul 110-744,
South Korea.
4 Department of Diagnostic Radiology, Asan Medical Center, University of Ulsan
College of Medicine, 388-1 Poongnap-dong, Songpa-gu, Seoul 138-736, South
Korea.
Received October 30, 2004;
accepted after revision February 22, 2005.
Address correspondence to B. Kim.
Abstract
OBJECTIVE. The purpose of this article is to present the
radiological findings of peripheral primitive neuroectodermal tumors that
arise in the retroperitoneum.
CONCLUSION. Peripheral primitive neuroectodermal tumors (PNETs)
arising in the retroperitoneum tend to be large and aggressive. Although the
imaging appearance of peripheral PNETs is nonspecific, these tumors should be
considered in the differential diagnosis when one encounters a large
retroperitoneal mass with aggressive features.
Keywords: CT imaging • genitourinary tract imaging • MRI
Introduction
Central and peripheral primitive neuroectodermal tumors (PNETs) exhibit
characteristic immunophenotypical and genetic features that distinguish them
from other small round cell tumors
[1]. Peripheral PNET arises
outside the central and sympathetic nervous systems and differs from central
PNET in that peripheral PNET typically expresses high amounts of the MIC2
antigen (CD99) and exhibits highly characteristic chromosomal translocation
[2]. Peripheral PNET is
uncommon, and the overall incidence is 1% of all sarcomas
[3]. This tumor can occur at
any age, although the peak age incidence is adolescence and young adulthood.
In general, PNET is a very aggressive neoplasm and it has a poor prognosis,
with a 5-year disease-free survival rate of 45–55%
[4]. The most common locations
of peripheral PNETs have been the thoracopulmonary region, the retroperitoneal
paravertebral soft tissues, the soft tissues of the head and neck, and the
intraabdominal and intrapelvic soft tissues and extremities
[4]. The incidence of
peripheral PNET in the abdomen and pelvis, including the retroperitoneum, is
about 14% of all peripheral PNETs
[4]. In most previous
peripheral PNET studies, researchers focused on their histologic features
[2,
5–7].
Peripheral PNET of the retroperitoneum has been described in a few
publications (fewer than 20 cases); it is sporadically reported in the kidney,
adrenal gland, and pelvis. These reports have described tumors of large masses
with areas of necrosis or hemorrhage, reflecting the aggressive nature of the
tumor [3,
8–11].
This article illustrates the radiologic findings of 10 cases of peripheral
PNET arising in the retroperitoneum (two in the adrenal gland, one in the
anterior pararenal space, three in the kidney, one in the perinephric space,
one in the periureteric space, and two in the presacral space) that were
gathered from three institutions (Sungkyunkwan University Samsung Medical
Center, the Seoul National University Hospital, and the Ulsan University Asan
Medical Center, Seoul, Korea) from March 1996 to July 2002
(Table 1). Nine patients were
examined with CT (one with a nonhelical scanner and eight with a helical
scanner) and five patients with MRI. Both unenhanced and contrast-enhanced CT
scans were performed for eight patients; a contrast-enhanced scan was
performed for one patient. A bolus of 100–120 mL of IV contrast material
(iopromide, Ultravist; Schering) was administered at a rate of 2–3
mL/sec. Scan delay was 45 sec with a nonhelical CT scanner and 60–70 sec
with a helical scanner. MR images were obtained using a 1.5-T unit with body
or phased-array coil. We performed the following pulse sequences: unenhanced
axial T1-weighted images (TR/TE, 400–600/11–19), multisection
T2-weighted images (2,000–3,000/80–100); and repeated T1-weighted
axial, sagittal, or coronal planes after IV injection of 0.1 mmol/kg of
gadopentetate dimeglumine (Magnevist, Schering). A dynamic scan was performed
immediately and at 60, 120, 180, and 300 sec for one patient. Tumors were
histologically confirmed by biopsy in six patients and surgery in four
patients. The radiologic findings were evaluated by two radiologists (one with
more than 15 years of experience in the genitourinary system and the other
with 6 years of experience) with consensus. The patient data and details are
shown in Table 1, and
radiologic findings according to the location of masses are summarized in
Table 2.
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Fig. 1A —Photomicrograph of histopathologic specimen of renal peripheral
primitive neuroectodermal tumor (PNET) from 30-year-old man (patient 6). Stain
shows diffuse infiltration of small round cells (H and E, x20).
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Fig. 1B —Photomicrograph of histopathologic specimen of renal peripheral
primitive neuroectodermal tumor (PNET) from 30-year-old man (patient 6).
Immunohistochemical stain for CD99 (MIC2) reveals strong reactivity for CD99,
which is typically detected not only in PNETs but also in Ewing's sarcoma
(original magnification, x4).
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Fig. 1C —Photomicrograph of histopathologic specimen of renal peripheral
primitive neuroectodermal tumor (PNET) from 30-year-old man (patient 6).
Immunohistochemical stain for neuronal marker shows strong reactivity for
neuron-specific enolase, which differentiates PNETs from other small round
cell tumors, such as Ewing's sarcoma and neuroblastoma.
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Histopathologic Features
Histologically, the tumors were composed of small undifferentiated
neuroectodermal cells (Figs.
1A,
1B, and
1C) and frequently showed
immunohistochemical and electron-microscopic features of divergent neuronal
differentiation. They were considered part of the spectrum of round cell
sarcoma, including neuroblastoma, Ewing's sarcoma, and Askin tumor, among
others [5]. These tumors
typically express high amounts of the MIC2 antigen (CD99)
[6] (Figs.
1A,
1B, and
1C) and exhibit highly
characteristic chromosomal translocation between chromosome 11 and 22 (t (11,
22)(q24;q12)) that results in the fusion of the Ewing's sarcoma gene with any
of several members of the Ewing's sarcoma/primitive neuroectodermal tumor
family of transcription factors, leading to oncogenic activation of the
Ewing's sarcoma gene [7]. They
possessed neuronal features with neurosecretory granules on electron
microscopy and immunohistochemical characteristics, such as positive staining
with neuron-specific enolase (Figs.
1A,
1B, and
1C), which made them a distinct
pathologic entity and differentiated them from other small round cell tumors,
such as Ewing's sarcoma and neuroblastoma
[2,
12,
13].
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Fig. 2A —25-year-old woman with peripheral primitive neuroectodermal tumor
arising in left adrenal gland who had palliative tumorectomy for right atrial
mass (patient 1). Contrast-enhanced CT image shows inhomogeneous enhancement
with large area of central necrosis (asterisk). Note tumor invasion
into inferior vena cava (IVC) (arrows).
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Fig. 2B —25-year-old woman with peripheral primitive neuroectodermal tumor
arising in left adrenal gland who had palliative tumorectomy for right atrial
mass (patient 1). CT of chest shows that tumor thrombus within IVC seen in
A extended into right atrium (arrows).
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Fig. 2C —25-year-old woman with peripheral primitive neuroectodermal tumor
arising in left adrenal gland who had palliative tumorectomy for right atrial
mass (patient 1). Photograph of gross specimen from palliative tumorectomy
shows tumor thrombus.
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Enhancement Pattern
Nine of 10 tumors were larger than 3 cm and showed heterogeneous
enhancement (Figs. 2A,
2B, and
2C), whereas one tumor measured
3 cm and showed homogeneous enhancement (Figs.
3A,
3B, and
3C).
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Fig. 3A —58-year-old man with peripheral primitive neuroectodermal tumor
arising in left perinephric space (patient 7). T2-weighted coronal image shows
relatively well-defined mass in perinephric space. Mass shows intermediate
signal intensity (arrows).
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Fig. 3C —58-year-old man with peripheral primitive neuroectodermal tumor
arising in left perinephric space (patient 7). On contrast-enhanced coronal
T1-weighted image, mass shows homogeneous, minimal enhancement
(arrows).
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Necrosis and Hemorrhage
The most common radiologic finding in our study was tumor necrosis, which
was found in seven of 10 patients. Three of these showed extensive central
necrosis with peripheral enhancement (Figs.
2A,
2B, and
2C), and four revealed single
or multifocal necrotic areas (Figs.
4A,
4B, and
4C).
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Fig. 4A —72-year-old man with peripheral primitive neuroectodermal tumor
arising in left anterior pararenal space (patient 3). Unenhanced CT scan shows
large hypodense mass in left upper abdomen (arrows).
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Fig. 4B —72-year-old man with peripheral primitive neuroectodermal tumor
arising in left anterior pararenal space (patient 3). Contrast-enhanced CT
scan shows inhomogeneous mass with ill-defined areas of low density,
suggesting necrosis (asterisks). Intervening fat between mass and
pancreas and left kidney was obliterated because of direct invasion by mass
(arrows). Mass also invades spleen and encases splenic artery and
vein (not shown).
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Fig. 4C —72-year-old man with peripheral primitive neuroectodermal tumor
arising in left anterior pararenal space (patient 3). Chest CT scan was
performed because of chest pain and shows right hilar (long arrows)
and mediastinal (short arrows) lymph nodes with left pleural effusion
(asterisk). Cytologic examination of pleural fluid revealed
metastatic disease.
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Five of the 10 tumors revealed hemorrhagic foci on CT or MR images (Figs.
5A,
5B, and
5C). Larger tumors appeared
heterogeneously enhanced with large areas of necrosis or hemorrhage. When the
tumor was less than 3 cm (a single lesion in this study), no evidence of
hemorrhage or necrosis was seen.
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Fig. 5A —32-year-old woman with peripheral primitive neuroectoderlng in
presacral region (patient 10). Sagittal T2-weighted MR image shows huge
presacral mass (arrows) occupying nearly entire pelvic cavity. Mass
displaces urinary bladder (B) anteriorly and rectum (R) posteriorly.
Low-signal septa were seen (curved arrows).
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Fig. 5C —32-year-old woman with peripheral primitive neuroectoderlng in
presacral region (patient 10). Contrast-enhanced axial T1-weighted MR image
reveals multiple cysts in peripheral portion of mass (arrows).
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Vascular Involvement
Vascular involvement was defined as a contour abnormality or tumor-induced
stenosis or occlusion and tumoral contact that exceeded one half of the
circumference of the vessel. It was seen in five patients.
Venous Thrombosis
Renal vein invasion was seen in four patients with peripheral PNETs that
arose in the adrenal gland, anterior pararenal space, and kidney
(Table 2). Peripheral PNETs
arising in the adrenal gland and kidney revealed tumor thrombi in the inferior
vena cava (IVC) (Figs. 6A,
6B,
6C, and
6D). Peripheral PNET arising
from the presacral space revealed tumor thrombi in the right iliac vein and
IVC (Figs. 7A,
7B, and
7C). In PNET arising from the
adrenal gland tumor, the thrombus was extended into the right atrium (Figs.
2A,
2B, and
2C).
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Fig. 6A —30-year-old man with peripheral primitive neuroectodermal tumor in
left kidney (patient 6). Axial T2-weighted MR image shows heterogeneous
intermediate- to high-signal mass (long arrows) with thrombus
(short arrows) in left renal vein and inferior vena cava.
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Fig. 6B —30-year-old man with peripheral primitive neuroectodermal tumor in
left kidney (patient 6). Photograph of gross specimen from nephrectomy shows
soft, yellow–tan large mass with necrotic focus (arrows) in
left kidney.
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Fig. 6C —30-year-old man with peripheral primitive neuroectodermal tumor in
left kidney (patient 6). Contrast-enhanced CT scan of chest was performed
because of dyspnea. Tumor emboli (arrows) in right interlobar and
segmental pulmonary arteries were histologically confirmed. Note subsegmental
infarct (curved arrows) of superior segment of right lower lobe.
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Fig. 6D —30-year-old man with peripheral primitive neuroectodermal tumor in
left kidney (patient 6). Photograph of gross specimen from embolectomy shows
representative tumor emboli in pulmonary and interlobar arteries.
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Fig. 7A —27-year-old man with right foot pain (patient 9). Contrast-enhanced
CT scan shows large presacral mass (long arrows) with multiple
septations (curved arrows) and nodular calcification (short
arrow).
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Fig. 7B —27-year-old man with right foot pain (patient 9). Contrast-enhanced
CT scan obtained caudad to A reveals protrusion of mass into right
sciatic notch (arrows), resulting in right foot pain. Urinary bladder
(B) is anteriorly displaced and invaded by mass. Urine cytology represents
malignant cells.
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Fig. 7C —27-year-old man with right foot pain (patient 9). Unenhanced CT of
lower abdomen shows tumor thrombus within inferior vena cava (long
arrows). Note nodular calcification (short arrow) at periphery
of thrombus.
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Arterial Involvement
Peripheral PNET arising from kidney tumor emboli was seen in both pulmonary
arteries; in this particular patient, thromboembolectomy was performed and
tumor cells were histologically confirmed in the IVC and pulmonary arteries
(Figs. 6A,
6B,
6C, and
6D). Peripheral PNET arising
from the anterior pararenal space showed extensive vascular invasion at the
celiac trunk, splenic and renal arteries, and veins (Figs.
4A,
4B, and
4C).
Organ Invasion
Organ invasion was present in four patients. Peripheral PNETs arising from
anterior pararenal space showed direct invasions into the pancreas, left
kidney, spleen, and stomach (Figs.
4A,
4B, and
4C); the mass in renal
peripheral PNET (patient 6) directly invaded into the adjacent psoas muscle.
The tumor arising in the periureteral space involved the ipsilateral ureter
(Figs. 8A and
8B) and resulted in
obstructive uropathy. The peripheral PNET arising from the presacral mass
(patient 9) invaded the urinary bladder anteriorly and rectum posteriorly.
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Fig. 8A —29-year-old man with peripheral primitive neuroectodermal tumor of
periureteric space (patient 8). Retrograde pyelogram shows space-occupying
lesion (arrows) around right ureter with contrast leak
(asterisk) from ureter.
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Fig. 8B —29-year-old man with peripheral primitive neuroectodermal tumor of
periureteric space (patient 8). Contrast-enhanced CT shows well-encapsulated
mass (arrows) around right distal ureter, which is compressed by
mass, resulting in obstructive hydroureteronephrosis. Curved arrow marks
contralateral ureter.
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Intratumoral Cyst and Septation
Septations were seen in three of four patients with intratumoral cysts and
presented as multicystic masses in two of four patients (Figs.
5A,
5B,
5C,
7A,
7B, and
7C). Peripheral PNET arising
from the kidney showed the mainly cystic tumor with an internal enhancing
nodule within the cystic mass (Figs.
9A and
9B); therefore, it mimicked
cystic renal cell carcinoma.
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Fig. 9A —45-year-old man with peripheral primitive neuroectodermal tumor
involving right kidney mimicking cystic renal cell carcinoma (patient 4).
Unenhanced CT scan shows hypodense mass (arrows) in central portion
of right kidney.
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Fig. 9B —45-year-old man with peripheral primitive neuroectodermal tumor
involving right kidney mimicking cystic renal cell carcinoma (patient 4).
Contrast-enhanced CT scan shows cystic renal mass (arrows) with
enhancing nodule (curved arrow).
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Calcification
Foci of calcification were seen in one patient (Figs.
7A,
7B, and
7C). In this patient,
calcified tumor thrombi were extended into the right iliac vein and IVC.
Several articles reported the presence of punctate and coarse intratumoral
calcifications [3].
Metastasis
Metastases at diagnosis were found in three patients. The site of
metastasis at the time of diagnosis was the lung (patient 1), supraclavicular
lymph node (patient 2), and the mediastinal lymph nodes and pleural fluid
(Figs. 4A,
4B, and
4C). All of these metastases
were histologically confirmed by biopsies or cytologic examination. At times
of diagnosis, 25–50% of PNETs were present with metastatic disease, and
metastases spread rapidly to the lung, lymph nodes, liver, and bones
[14].
In summary, peripheral PNETs arising in the retroperitoneum tend to be
large and aggressive. These tumors commonly showed heterogeneous enhancement
with internal hemorrhage and necrosis. They might be locally aggressive with
vascular invasion and invasion of adjacent organs and have metastatic
potential. Sometimes these tumors may show internal septations or
calcification. Although the imaging appearance of peripheral PNETs is
nonspecific, these tumors should be considered in the differential diagnosis
when one encounters a large retroperitoneal mass with aggressive features.
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Abstract
Introduction
