Indian Journal of Vascular and Endovascular Surgery

: 2017  |  Volume : 4  |  Issue : 1  |  Page : 20--22

Malignant Triton Tumor: Role of Electron Microscopy in Determining Differentiation

Indrani Sen1, Rekha Samuel2, Jennifer Prabhu3, Albert Abhinay Kota1, Sunil Agarwal1,  
1 Department of Vascular Surgery, Christian Medical College, Vellore, Tamil Nadu, India
2 Centre for Stem Cell Research, Christian Medical College, Vellore, Tamil Nadu, India
3 Department of General Pathology, Christian Medical College, Vellore, Tamil Nadu, India

Correspondence Address:
Albert Abhinay Kota
Department of Vascular Surgery, Christian Medical College, Vellore, Tamil Nadu


Malignant triton tumors (MTTs) are peripheral nerve sheath tumors: Perivascular origin is extremely rare. We report a sporadic perivascular MTT in a 37-year-old man. He presented with a swelling in the right popliteal fossa. Imaging revealed a solid lesion adherent to the popliteal artery. He underwent en bloc excision of the tumor with repair of the popliteal artery. We studied the histopathology and electron microscopy (EM) features of this tumor. He received local radiotherapy and remains disease-free at 2 years. EM may help prognosticate tumor behavior when these tumors occur in rare/nonneural locations.

How to cite this article:
Sen I, Samuel R, Prabhu J, Kota AA, Agarwal S. Malignant Triton Tumor: Role of Electron Microscopy in Determining Differentiation.Indian J Vasc Endovasc Surg 2017;4:20-22

How to cite this URL:
Sen I, Samuel R, Prabhu J, Kota AA, Agarwal S. Malignant Triton Tumor: Role of Electron Microscopy in Determining Differentiation. Indian J Vasc Endovasc Surg [serial online] 2017 [cited 2020 Dec 1 ];4:20-22
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Full Text


Malignant triton tumors (MTTs) are peripheral nerve sheath tumors: Perivascular origin is extremely rare. We descibe the management of such a case.

 Case Report

Clinical presentation and operative details

A 37-year-old male presented with a single, nontender, gradually progressive swelling in the right popliteal fossa for 3 months. He did not complain of paresthesia, weakness, limb swelling, or claudication. There was no history of trauma, allergies, drug abuse, or other systemic diseases. On examination, there was an 8 cm × 6 cm firm nonpulsatile swelling in the right popliteal fossa. There was no inguinal lymphadenopathy, and the neurovascular examination was normal.

Magnetic resonance imaging (MRI) revealed a uniformly hyperintense mass adherent to the right popliteal artery. The differentials considered were a soft tissue tumor or a thrombosed pseudoaneurysm - the former was confirmed on duplex ultrasound. He underwent excision of the tumor. A posterior approach was used for control of the popliteal artery - the tumor was densely adherent to the artery. It was completely separate from the tibial nerve which coursed more laterally [Figure 1]a. The tumor was excised en bloc with the artery. This was reconstructed with an interposition vein graft [Figure 1]b. The patient's postoperative recovery was uneventful. He did not develop any neurological deficit, and his distal pulses were normal. He received local radiation therapy postprocedure. He had a good clinical outcome with no tumor recurrence or metastasis at 2-year follow-up. He consented for the publication of this report.{Figure 1}

Histopathology and electron microscopy

The tumor did not have intraluminal extension [Figure 1]c. Histopathology of the tumor revealed fascicles of neoplastic spindle cells in a myxoid stroma with rhabdomyoblastic differentiation [Figure 2]. Lipoblasts were not seen. Mitotic activity was 6/high-power fields. Immunohistochemistry showed diffuse positivity of the tumor cells for S100. There was focal positivity for CD34 and bcl2. The rhabdomyoblasts were positive for desmin and myogenin. The absence of SYT-SSX1 and SYT-SSX2 translocation by quantitative reverse transcriptase polymerase chain reaction ruled out synovial sarcoma. A diagnosis of malignant peripheral nerve sheath tumor (MPNST) with rhabdomyoblastic differentiation (triton tumor) was made. However, the origin of this rare tumor was not clear. Hence, we proceeded for transmission electron microscopic examination, Tecnai T12 Spirit, FEI which showed predominantly tumor cells with long interdigitating cytoplasmic processes [Figure 3], some with the continuous basal lamina. Several cells had abundant mitochondria, polyribosomes, and some contained dense granules. Tumor cells were located in a perivascular location. Occasional luse bodies were present. Interspersed epithelioid cells with convoluted nuclei and short cytoplasmic processes were also seen. This confirmed the origin to be perivascular in nature.{Figure 2}{Figure 3}


Malignant triton tumors (MTTs) were first described by Masson and named by Woodruff and Locatelli.[1] Clinical presentation is similar to other soft tissue tumors. They occur in all parts of the body, but the involvement of the extremities is less commonly reported than the head and neck or retroperitoneum. Preoperative diagnosis of the tumor is by multimodality imaging (computed tomography/MRI/ultrasound). Imaging assesses the local extent and helps plan resection but does not allow differentiation from other MPNSTs. Treatment is radical excision and postoperative radiotherapy. Recurrence rates are high with a dismal 5-year survival rate (about 11%), which is worse when compared to other MPNSTs. Large size, site (retroperitoneum, buttock), histological subtype, and distant metastases at diagnosis are poor prognostic factors.

MTTs are diagnosed in 10% of MPNSTs. They arise from Schwann cells or pluripotent neural crest cells; 25%–50% are associated with neurofibromatosis (NF).[2] Sporadic tumors in non-NF patients can occur.[3] Nerve origin may not be identified in 44%–61% of cases even when the patient is a diagnosed case of NF.[4],[5] Histopathological diagnosis is by Daimaru criteria – the presence of Schwann cells with rhabdomyoblastic differentiation in the tumor.

The exact pathogenesis as to why the rhabdomyoblastic differentiation worsens prognosis is not understood. The behavior and features of those arising from atypical (nonneural sites) are thought to be less aggressive, but due to the rarity of these tumors, literature is sparse. Demonstration of perineural differentiation is associated with an overall better survival.[6] This may be seen even in sporadic tumors atypical/perivascular sites, which have no connection to a peripheral nerve.[7],[8] Electron microscopy (EM) has been used for confirming the diagnosis of MTT in tumors arising from nerves and in differentiating benign from malignant tumors.[9],[10],[11],[12]

We performed EM to study tumor origin and differentiation in this patient with sporadic malignant MTT. EM helped establish the tissue of origin of this MTT to definitively differentiate it from other perivascular tumors. EM features were of a well-differentiated tumor with luse bodies which was suggestive of perineural differentiation.[12] This was proved in this patient only by EM as the intraoperative, and histopathology had not been able to demonstrate relation to a peripheral nerve. The good clinical outcome in a malignant tumor with such a differentiation has to be studied in larger cohorts to determine if EM should be used in all sporadic MTTs as a prognostic factor.


The use of EM to determine origin and differentiation in sporadic MTT as seen may help in prognosticating response to therapy, especially in rare instances of origin in nonneural locations.


We would like to acknowledge the Department of General Pathology, Histopathology Core Facility, Centre for Stem Cell Research and Central EM Facility, Christian Medical College and Hospital for their technical assistance.

Financial support and sponsorship

Olympus BX53 microscope, color digital camera DP21 procured on the Department of Science and Technology, Science and Engineering Research Council SB/FT/LS-196/2012 to R. Samuel.

Conflicts of interest

There are no conflicts of interest.


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