Case Report Peripheral Nerve Sheath Tumors. Benign or Malignant? The Role of MRI and Ultrasonography in A Case Report Alexandros Chatzistefanou, MD, Michalis Mantatzis, MD, PhD, Savas Deftereos, MD, PhD, Paraskevi Mintzopoulou, MD, Panos Prassopoulos, MD, PhD From the Department of Radiology, Democritus University of Thrace, University Hospital of Alexandroupolis, Alexandroupolis, Greece
ABSTRACT A 31-year-old male patient admitted to another hospital for investigation of a localized painful hump in the medial surface of his left leg. The clinical examination revealed a painful palpable lump in the medial surface of left thigh that was initially thought to be a hematoma due to a history of recent trauma. However, an ultrasound was requested to exclude deep venous thrombosis (DVT). The US examination revealed a heterogeneous, fusiform lesion with elongated proximal and distal projections in close proximity to superficial femoral artery and vein and could not definitely exclude the DVT hypothesis. In a second ultrasound examination performed in our department, a neurogenic origin of the lesion was proposed. A consequent MRI examination confirmed the presence of a fusiform tumor in the anatomic path of the saphenous nerve. This was further confirmed intraoperatively, and pathologically was diagnosed as a malignant peripheral nerve sheath tumor (MPNST). In this present study the role of ultrasonography, the correlation between MRI and ultrasonographic findings are discussed and a review of the literature is presented.
Introduction Soft-tissue tumors are not uncommon, most of them being benign.1 Considering this observation, confronting a mass-like lesion at the extremities with no clear relation to bones, a soft tissue neoplasia should be ruled out. Malignant peripheral nerve sheath tumors (MPNSTs) include all malignant tumors with neural differentiation arising from peripheral nerves and account for 5–10% of all malignant soft tissue tumors with approximately two-thirds of them accompanied by neurofibromatosis I (NF-1) (von Recklinghausen’s disease).2 Sporadic MPNST may occur as secondary neoplasms after radiation therapy with a latency of up to two decades. Several imaging modalities have been described in the assessment of soft-tissue tumors, including plain radiography, ultrasonography (US), computed tomography (CT), magnetic resonance imaging (MRI), angiography, and positron emission tomography (PET).3 However, none of these approaches are reliable for distinguishing benign from malignant lesions with reported criteria suggestive of malignancy, varying widely.
Case Presentation We present a case of an otherwise healthy 31-year-old patient, who complained of a painful, localized swelling on the median surface of his left mid-thigh. The initial work-up was performed in another hospital. The clinical examination revealed a painful
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Acceptance: Received February 12, 2012, and in revised form April 3, 2012. Accepted for publication May 6, 2012. Correspondence: Address correspondence to Michalis Mantatzis, MD, PhD, Department of Radiology, Democritus University of Thrace, University Hospital of Alexandroupolis, Opsikiou 1, 681 00, Alexandroupolis, Greece. E-mail:
[email protected]. J Neuroimaging 2014;24:308-310. DOI: 10.1111/j.1552-6569.2012.00731.x
palpable lump in the medial surface of left thigh. Due to a history of recent trauma and rather unspecific clinical signs, it was initially attributed to a hematoma. An ultrasound that was performed to exclude deep venous thrombosis (DVT) revealed a spindle shaped soft tissue mass of mixed echotexture and posterior acoustic enhancement. The lesion had elongated proximal and distal projections in close proximity to superficial femoral artery (SFA) and Femoral Vein (FV; former Superficial Femoral Vein; SFV). Although there were no signs of thrombosis in FV, the possibility of a doubled FV with a thrombosed branch was questioned. The patient was referred to our department for further investigation. A repetitive ultrasound clarified that despite the proximity of the central portion of the lesion with the SFA and FV (Fig 1), the peripheral elongated part was gradually diverged from the vascular bundle ensuing a more superficial and anterior route along the expected route of saphenous nerve, thus suggesting a possible diagnosis of neurogenic tumor. Moreover, the middle part of the lesion was bulged, having a rather mass-like appearance, further moving out from the initial assumption of a lesion having vascular origin. The borders of the lesion were clearly separated from sartorius muscle, which however was greatly dislocated. A color Doppler examination revealed intrinsic anarchic vascular pattern and a spectral waveform consistent with neo-angiogenesis. To further characterize the lesion, an magnetic resonance imaging (MRI) examination of the left thigh was performed. A
◦ 2012 by the American Society of Neuroimaging C
Keywords: Peripheral Nerve Tumors, MRI, Ultrasonography, Power Doppler.
Fig 1. (A) Gray scale ultrasound-panoramic view of the lesion clearly demonstrates the mass-like appearance of the central part with mixed echotexture, posterior acoustic enhancement and elongated proximal and distal projections. The proximal projection is located superficially to the deep vascular structures of the thigh (arrow) whereas no anatomic continuation is exhibited. (B) Power doppler US of the central part of the lesion, depicts an anarchic vascular structure, with vessel caliber alterations (long arrow) and loops (short arrow), suggesting malignancy.
mass at the medial surface of the left thigh was demonstrated (dimensions: 5 cm × 4.3 cm × 3.9 cm) as was expected (Fig 2). Furthermore a proximal as well as a distal fusiform projection of the bulged middle part was confirmed. The advantageous capabilities of multiple anatomic orientations of MRI clarified with a high degree of confidence, the anatomic correlation of the lesion with the adjacent structures. The proximally located fusiform projection showed close proximity with the SFA, whereas the distal part deviated from the superficial femoral vessels to a location between the sartorius and the vastus medialis
Fig 2. MRI of the thigh: (A) Coronal T2-WI demonstrates inhomogeneous high signal intensity of the lesion, with morphologic characteristics similar to the prior ultrasound examination. Of note: the separating band of fat between the lobular part of the lesion and the muscle, indicating that the sartorious muscle is not infiltrated. (B) T1WI after contrast administration shows inhomogeneous pattern of enhancement with the distal part of the lesion gradually deviating from the deep vascular structures (arrow).
muscle. The lesion exhibited inhomogeneous, low to intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images, without suppression of fat signal in the respective sequences and a nonhomogeneous pattern of enhancement. In addition, MR examination proved that the sartorius muscle was deviated but not infiltrated, since there was a separating band of fat between the lobular part of the lesion and the muscle.
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Given the imaging findings, the patient’s age and symptoms, the differential diagnosis included neurofibroma, MPNST, and less possibly angiosarcoma. The patient was operated and histologic examination confirmed the diagnosis of MPNST of the saphenous nerve.
Discussion The investigation of a swollen painful lower limb includes a relatively long list of variable clinical entities. Among them DVT is highly ranked in the differential diagnosis and should be ruled out confidently, although less common entities, such as soft tissue masses should be kept in mind. Among them, neurogenic tumors may render the differential diagnosis difficult, since these masses have elongated shape, resembling a vascular structure. Interestingly in our case, the proximity of the lesion with the SFA and FV, the elongated appearance in ultrasound of proximal and distal part, as well as the nonspecific imaging characteristics, initially led to a diagnosis consistent with DVT. The obscured history of recent trauma was further misleading, because the clinically palpable lesion could be attributed to a hematoma. The role of US however, was not restricted in the exclusion of DVT. By combining gray scale imaging characteristics, Color Doppler Sonography (CDS), Power Doppler Sonography (PDS), and Spectral waveform analysis (SWA), a possible malignant tumor of neurogenic origin, was suggested. Although gray-scale US has a high sensitivity for tumor detection, it has not proven useful in differentiating benign from malignant conditions.4-6 Several ultrasonographic findings such as the presence of extensive central necrosis/hemorrhage, illdefined margins, and infiltration of adjacent tissues, edema, calcification, and a diameter of >5 cm may raise the suspicion of a malignant peripheral nerve tumor however, they are not considered highly specific.7,8 The analysis of further ultrasonographic parameters such as CDS, PDS, and SWA may have a major contribution. There are reports in literature indicating that vascular architecture analysis using the above techniques may facilitate differentiation of benign and malignant lesions, demonstrating occlusions, stenoses, shunts, trifurcations, and loops, all of which constitute a possible diagnosis of malignancy.9 In our case the lesion demonstrated inherent reticular vessel architecture, with vessel loops, stenoses, as well as consecutive vessel caliber alterations. The SWA clearly demonstrated an arterial flow pattern, thus excluding the less possible case of a long standing DVT with signs of recanalization. Moreover, a low RI further led towards neoangiogenesis. These are significant advantages of ultrasound over MRI that although exhibits high contrast resolution, cannot assess flow dynamics and vascular patterns. Computed tomography (CT) has a limited role in the investigation and characterization of soft tissue masses, due to the overlap of imaging characteristics of benign and malignant neurogenic tumors.10 Imaging findings that may suggest malignancy may be a more prominent pattern of heterogeneity as well as
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higher attenuation values in unenhanced CT, compared to benign neurogenic tumors.11 MRI is the modality of choice for assessing soft tissue masses combining the multiplanar imaging capabilities with the inherent multiple ways for tissue contrast differentiation using different sequences. Furthermore, the clarification of the anatomical relationships of tumor with the surrounding tissues is better delineated. Contrast-enhanced MRI rarely provides additional information not available from other MRI sequences.12 In our case nevertheless, contrast administration clearly depicted tumor’s extent and deviation from the vascular structures. Limitations for MR Imaging include the difficulty in evaluating the tumor’s vascular pattern and the inability of differentiating between arterial and venous vessel origin. CDS and PDS have a valuable role in this regard. In conclusion, ultrasonographic findings in our case provided valuable information for the tumor’s origin and suggested possible malignancy according to its vascular architecture, underlining the principal role of ultrasonography in the evaluation of soft tissue tumors, especially when they are superficially located.
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