Sojun Hoshimoto,1Zenichi Morise,1 Chinatsu Takeura,1Masahiro Ikeda,1 Tadashi Kagawa,1Yoshinao Tanahashi,1 Yasuhiro Okabe,1Yoshikazu Mizoguchi,2 Atsushi Sugioka1
1Department of Surgery and 2Department of Pathology, Fujita Health University School of Medicine, Toyoake, Aichi, Japan
Abstract
We report an extremely rare case of malig-nant Triton tumor developing in the retroperi-toneal space in a patient with neurofibromato-sis type 1. A 21-year old man who had been diagnosed with neurofibromatosis type 1 was admitted to our hospital with the chief com-plaint of a palpable abdominal mass. Abdominal computed tomography revealed a huge hetero-geneous tumor measuring approximately 17 cm in diameter occupying the left retroperi-toneal space, and numerous metastatic lesions between the left psoas muscle and the left thigh with dissolution of the left hip joint. After the diagnosis of a retroperitoneal malignant neuro-genic tumor, resection of the tumor with recon-struction of the abdominal aorta was conduct-ed, followed by postoperative transarterial infu-sion chemotherapy. The histopathological diag-nosis was malignant peripheral nerve sheath tumor with rhabdomyosarcomatous differentia-tion, namely malignant Triton tumor.
Postoperative chemo-therapy was in vain and the patient died 14 months after the surgery as a result of lung metastasis.
Introduction
Malignant Triton tumor (MTT) is a histolog-ical variant of malignant peripheral nerve sheath tumors (MPNSTs) with rhabdomyosar-comatous differentiation. Although MPNSTs have been known to develop in cases of neu-rofibromatosis type 1 (von Recklinghausen’s disease, NF-1) and sometimes to occur in the retroperitoneal space, there are few reports of MTTs developing in the retroperitoneal space.
We report an extremely rare case of MTT devel-oping in the retroperitoneal space in a patient with NF-1 and describe the clinicopathological features of this tumor.
Case Report
A 21-year old man, who had been diagnosed to have NF-1 by a dermatologist when he was about a year old, was referred to Fujita Health University Hospital in November 2004, because of a left lower abdominal mass and gradually increasing pain in the same region.
Physical examination revealed many café-au-lait spots, subcutaneous masses of various sizes, scoliosis, and a firm fixed mass in the left lower abdomen the size of a baby’s head.
The left lower extremity was markedly swollen and the patient had difficulty in walking.
Laboratory examination revealed slight ane-mia and elevated serum CRP; however, other serum chemistry data were within normal lim-its. Abdominal computed tomography revealed a huge heterogeneous tumor approximately 17 cm in diameter occupying the left retroperi-toneal space (Figure 1). Numerous other tumors, which seemed to be metastatic lesions, were found between the left psoas muscle and the left thigh with dissolution of the left hip joint (Figure 2). On magnetic reso-nance imaging, the tumor was visualized as a low intensity signal on T1-weighted images and as a high intensity signal on T2-weighted images.
After the diagnosis of retroperitoneal malig-nant neurogenic tumor associated with NF-1, a laparotomy was performed. A giant, firm, whitish, well-capsulated tumor was found occupying the left abdomen (Figure 3).
Although the main tumor appeared to be tight-ly adherent to the psoas muscle and to involve the abdominal aorta, there was no gross inva-sion of other adjacent organs. Resection of the main tumor and of the nodules in the retroperitoneal space that were suspected to be metastatic lesions and reconstruction of the abdominal aorta were conducted.
Macroscopically, the extirpated main tumor measured 19x15x13 cm in size and was encap-sulated. The cut surface of the tumor revealed solid and yellowish tissue in the peripheral portion and foci of hemorrhage and necrosis in the central portion of the tumor. Histo-pathological examination revealed
spindle-shaped cells with wavy nuclei and slightly eosinophilic cytoplasm, showing dense prolif-eration and forming storiform structures, with a myxomatous stroma (Figure 4A). On immunostaining, the spindle-shaped tumor cells showed a positive response for S-100 pro-tein and NSE, with sporadic distribution of rhabdomyoblastic cells that showed positive staining for myoglobin and desmin (Figure 4B). Immunohistochemical staining with S-100 and desmin indicated that the tumor cells originated from Schwann cells and showed rhabdomyosarcomatous differentiation. Based on these findings, a diagnosis of MTT associat-ed with MPNST was made.
After surgical treatment, transarterial infu-sion chemotherapy was administered via the left common iliac artery for the remnant tumors in the left hip joint and the left thigh, and the patient was discharged five months after the surgery. However, eight months after being discharged, the patient was readmitted for dyspnea found to be caused by lung metas-tasis. Despite administration of transarterial chemotherapy, the tumors increased greatly in size, and the patient died 14 months after the surgery. An autopsy was not performed.
Correspondence: Sojun Hoshimoto, Department of Surgery, Fujita Health University School of Medicine, 1-98 Dengakugakubo, Kutsukake-cho, Toyoake, Aichi 470-1192, Japan.
E-mail: [email protected]
Key words: malignant Triton tumor, malignant peripheral nerve sheath tumor, neurofibromato-sis, retroperitoneal tumor.
Conflict of interest: the authors report no con-flicts of interest.
Received for publication: 20 July 2009.
Accepted for publication: 5 August 2009.
This work is licensed under a Creative Commons Attribution 3.0 License (by-nc 3.0)
©Copyright S. Hoshimoto et al., 2009 Rare Tumors 2009; 1:e27
doi:10.4081/rt.2009.e27
Figure 1. Abdominal computed tomography showing a huge tumor occupying the left retroperitoneal space and a metastatic mass in the left psoas muscle (arrows).
Discussion
NF-1 is an autosomal dominant disorder characterized by café-au-lait spots, cutaneous neurofibromas, skeletal dysplasias, Lisch nod-ules, and sometimes malignant tumors, and it occurs with an incidence of approximately one in 3000 live births.1MPNSTs are well known to arise from major and minor peripheral nerves or within pre-existing neurofibromas, and approximately 50 percent of patients with MPNSTs have NF-1.2,3 The World Health Organization coined the term MPNST in place of the previously used, often confusing, termi-nology such as “malignant schwannoma,”
“malignant neurilemmoma,” “neurogenic sar-coma,” and “neurofibrosarcoma.”4The precise cell of origin of MPNSTs has not yet been con-clusively identified, although the Schwann cell is thought to be the major candidate cell for this. The overall five-year survival rate in patients with MPNSTs has been reported to be 34-44%, and the association of these tumors with NF-1 is predictive of a poor prognosis.2,3 The capacity of MPNSTs to undergo focal divergent differentiation is well known, and tumors showing rhabdomyosarcomatous dif-ferentiation, referred to as MTTs, are
identi-fied in approximately 12 percent of patients with MPNSTs.2
Woodruff et al. (1973) reported a series of 10 cases of malignant schwannoma with rhab-domyoblastic differentiation, which they were the first to refer to as MTTs.5 Immunohi-stochemical staining for skeletal muscle mark-ers such as myoglobin or desmin is essential for making a correct diagnosis of MTT, because of the histological variations of MPNSTs. The average age of patients with MTTs is 31.7 years and these tumors occur with approxi-mately equal frequency in males and females.6 The reported incidence of MTTs occurring in association with NF-1 is in the range of 44-69.
Several authors have reported that MTTs are
associated with a worse prognosis than MPNSTs, regardless of whether or not they are associated with NF-1,7,8 with a five-year sur-vival rate of 12-26%.6,7
The reason for the more aggressive behav-ior of MTTs than classic MPNSTs still remains unclear. MTTs occur predominantly in the trunk, head and neck, and lower extremities.8 According to a review of 75 cases of MTTs by Yakulis et al. (1996), the tumor was located in the retroperitoneum in only one case (1.3%).6 Subsequent to the publication of this review, we could identify only one case of retroperi-toneal MTT by a PubMed search of the English language literature using the terms “retroperi-toneum” or “retroperitoneal” and “Triton.”9All the three cases of MTTs developing in the retroperitoneal space reported so far, including the present case, presented with a huge abdominal mass,6,9since these retroperitoneal tumors are often asymptomatic in the earlier stages.
Like most soft-tissue sarcomas, MTTs tradi-tionally are insensitive to chemotherapy and radiotherapy. However, several authors have reported recently that repeated resection com-bined with chemotherapy and/or radiotherapy against recurrent MTTs might prolong the sur-vival in patients with MTTs.10,11 Because MPNSTs and MTTs have a high malignant potential, patients with NF-1 should be fol-lowed by periodic check-ups, including com-puted tomography for early detection of such tumors as these, and multidisciplinary treat-ments including complete resection are required for patients with MTTs.
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Case Report
Figure 3. At laparotomy, a well-capsulated tumor was found occupying the left abdomen.
Figure 4. (A) Spindle-shaped cells showing dense proliferation and forming storiform structures (H-E stain, x200), (B) staining for desmin was strongly positive in the area of MTT (peroxidase-antiperoxidase technique, x100).
Figure 2. Multiplanar reformation images revealed lateral depression of the abdomi-nal aorta by the main tumor (arrow heads), and numerous metastatic lesions between the left psoas muscle and the left thigh, with dissolution of the left hip joint (arrows).
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