Abstract

OBJECTIVE. We surveyed the clinical symptoms and radiologic features of ancient schwannoma, a rare variant of schwannoma characterized by degenerative changes.
MATERIALS AND METHODS. We present the clinical, radiologic, and pathologic features in seven patients with ancient schwannoma (mean age, 62 years; range, 45–80 years) treated at our department between 1998 and 2003.
RESULTS. The most characteristic clinical features were a sign like Tinel's sign and a long interval between the onset of symptoms and surgery (mean interval, 8.3 years). Ancient schwannomas can grow large; the biggest tumor seen in our study was 14 cm long. The highly accurate radiologic assessment made possible with contrast-enhanced MRI and CT scanning showed enhancement at a peridegenerative area and sometimes at a capsule. These findings differ from those of the typical schwannoma and neurofibroma patterns reported to date. Furthermore, bone scintigraphy showed uptake in the tumor, but no accumulation was seen on gallium-67 citrate scintigraphy.
CONCLUSION. The characteristic clinical and radiologic findings of ancient schwannoma should make it possible to differentiate it from malignant tumors.

Introduction

Schwannoma, one of the most common soft-tissue tumors, is a benign tumor that arises from the Schwann cells of the nerve sheath and presents with symptoms of pain or paresthesia. Ancient schwannoma, a degenerative neurilemmoma, is a schwannoma subtype characterized by degeneration and diffuse hypocellular areas. These changes are believed to occur because it takes a long time for schwannomas to develop [1]. Schwannomas with these degenerative changes can be misdiagnosed as sarcomas or as other forms of soft-tissue neoplasms. In this report, we describe the clinical symptoms and radiologic features of ancient schwannoma as an aid for preoperative differential diagnosis.

Materials and Methods

The seven patients entered into this study were diagnosed at pathology as having 24 schwannomas that were treated surgically in our department between 1998 and 2003. None of the patients had a history of Recklinghausen's disease. The tumors originated from the tibial nerve in three cases and in one case each from the lateral cutaneous femoral nerve, sciatic nerve, sural nerve, and plantar digital nerve.
Sonography, radiography, CT, MRI, bone scintigraphy, and gallium citrate scintigraphy were all used for the examination. A 1.5-T superconductive MRI unit (Signa, GE Healthcare) was used to produce spin-echo images. T1-weighted MRI with TR/TE (ranges, 500–716/12–17) and T2-weighted imaging (ranges, 3,000–4,000/81.3–100) using a body coil and field of view of 30–40 cm depending on body size were performed for all patients. Gadolinium-enhanced scans at a dosage rate of 0.2 mL/kg were obtained for all patients, and all underwent sonography, radiography, CT, and MRI. Six patients underwent bone scintigraphy, five underwent 67Ga citrate scintigraphy, and four underwent contrast-enhanced CT. Images from all patients with ancient schwannoma who underwent radiologic examinations were interpreted independently by three authors who reached agreement by consensus. After the radiologic examinations, the tumors were surgically treated and evaluated for pathology. The radiologic features of the tumors were then assessed and compared with the MRI findings for the pathologic specimens.

Results

Clinical Features of Ancient Schwannoma

The clinical records of the seven patients are summarized in Table 1. Tenderness and numbness were the most frequent symptoms, but five patients reported radiating pain produced by tapping on the tumor (Tinel's sign). The mean interval between onset of symptoms and surgery was 8.3 years (range, 1–20 years). All ancient schwannomas were located in the lower limbs except for one in a retroperitoneal space.
TABLE 1 Patient Data for Ancient Schwannoma
Patient No.Age (yr)SexLocationSize (cm)SymptomsTinel SignTime from Onset to Admission (yr)
166MSural nerve14Pain, numbness, palpable massPresent6
264FPlantar digital nerve6Pain, numbness, palpable massPresent13
380FTibial nerve5Contact pain, numbness, palpable massPresent20
461FTibial nerve3Pain, palpable massAbsent8
545MTibial nerve5Pain, palpable massPresent8
663FLateral cutaneous nerve of thigh (retroperitoneum)8NumbnessPresent2
7
58
F
Sciatic nerve
9
Palpable mass
Absent
1

Radiologic Features of Ancient Schwannoma

Radiologic features of the ancient schwannomas are summarized in Table 2.
TABLE 2 Features of Ancient Schwannomas in Seven Patients
FeatureNo. Found
Enhancement 
    In areas near degeneration 
        On CT4/4
        On MRI7/7
    In capsule on MRI5/7
Increased bone scintigraphy uptake6/6
Gallium-67 citrate scintigraphy uptake0/5
Histologic specimen 
    Calcification2/7
    Ossification
1/7
Sonography.—Sonograms showed a well-defined mass containing internal highly reflective areas or hypoechoic areas. An adjacent nerve was visualized in four cases.
CT.—CT scans showed a well-defined mass, and enhancement was observed in capsules or pericystic areas after IV contrast medium infusion (Figs. 1A and 1B). Enhancement of areas surrounding degeneration was seen in all patients who underwent enhanced CT.
Fig. 1A. CT evaluation in 80-year-old woman with ancient schwannoma. Axial CT scan of lower leg shows large, well-circumscribed low-density mass with partial central high-density area in posterior compartment.
Fig. 1B. CT evaluation in 80-year-old woman with ancient schwannoma. Contrast-enhanced CT scan shows enhancement in circumference of degenerative area and peripheral rim.
MRI findings compared with pathologic specimen results.—The gross appearance of the tumor was well circumscribed with a thin fibrous capsule, and the internal matrix was yellowish with some scattered myxoid areas and hemorrhagic, cystic, and necrotic areas ranging from red to brown (Figs. 2D and 3D).
Fig. 2D. MRI and histologic findings in 60-year-old man with ancient schwannoma. Photograph shows gross appearance of tumor. Squares show circumference of degenerative areas (E), area of degenerative change (F), and substance (G).
Fig. 3D. MRI and histologic findings in 56-year-old woman with ancient schwannoma. Photograph of gross appearance of tumor shows marked degeneration.
Microscopic examination showed that the tumors consisted mostly of Antoni type B areas that show low signal intensity on T1-weighted MR images and high signal intensity on T2-weighted images. Perivascular hyalinization and gapped vessels with organizing thrombus and hematoma or cystlike spaces mimicking vascular structures were clearly visible. These degenerative areas of hematoma or cystic formations varied in size. Contrast-enhanced MRI depicted these lesions as of various signal intensities without any enhancement. Both the Antoni type A and Antoni type B areas were enhanced by IV contrast medium. The nonenhancing areas of the tumor appeared in all cases to be areas of hemorrhage or degeneration. The circumference of these lesions was clearly enhanced, and the fibrous capsule of the tumor was sometimes enhanced. In all patients, enhanced areas surrounded the degenerative lesions, and enhancement in the capsule was seen on MRI in five patients. The Antoni type A area was reduced and seen mostly around the degenerative lesions (Figs. 2A, 2B, 2C, 2D, 2E, 2F, 2G and 3A, 3B, 3C, 3D). Calcification was histologically confirmed in two tumors, and ossification in one patient.
Fig. 2A. MRI and histologic findings in 60-year-old man with ancient schwannoma. Axial T1-weighted MR image shows large well-circumscribed mass with isointense signal. Note round high-signal-intensity area (arrow) in mass.
Fig. 2B. MRI and histologic findings in 60-year-old man with ancient schwannoma. T2-weighted image shows most of tumor as hyperintense signal and partially heterogeneous signal in internal oval area. Note areas of Antoni A (arrow) and Antoni B (arrowhead) tumor.
Fig. 2C. MRI and histologic findings in 60-year-old man with ancient schwannoma. Gadolinium contrast-enhanced image shows enhancement at circumference of degenerative lesion (arrow), peripheral rim (arrowhead), and substantial part.
Fig. 2E. MRI and histologic findings in 60-year-old man with ancient schwannoma. Photomicrograph shows Antoni A area. (H and E, ×100)
Fig. 2F. MRI and histologic findings in 60-year-old man with ancient schwannoma. Photomicrograph clearly shows hematoma and degenerative collagen tissue. (H and E, ×100)
Fig. 2G. MRI and histologic findings in 60-year-old man with ancient schwannoma. Photomicrograph clearly shows Antoni B area. (H and E, ×100)
Fig. 3A. MRI and histologic findings in 56-year-old woman with ancient schwannoma. Axial T1-weighted MR image of adductor magnus shows large tumor with isointense signal.
Fig. 3B. MRI and histologic findings in 56-year-old woman with ancient schwannoma. T2-weighted image shows heterogeneous tumor with high signal intensity in internal oval area (arrow).
Fig. 3C. MRI and histologic findings in 56-year-old woman with ancient schwannoma. Gadolinium contrast-enhanced image shows enhancement in circumference of degenerative area (arrowhead) and peripheral rim of tumor (star). Oval degenerative area (arrow) is not enhanced.
Bone scintigraphy and 67Ga citrate scintigraphy.—Moderate to high uptake in the tumor was seen in five cases on the bone scintigram, but 67Ga citrate scintigraphy showed no such accumulation in six cases.

Discussion

Schwannomas are benign slow-growing encapsulated tumors of nerve sheath origin that are found most commonly in the extremities. Their histology generally displays a biphasic pattern with areas of highly ordered cellularity (Antoni type A) and less cellular areas where a highly myxoid matrix predominates (Antoni type B) [2]. As for the radiologic findings, sonography of ordinary schwannomas shows a well-defined hypoechoic mass located along a nerve and eccentric to the nerve axis [3]. The CT appearance has been described as a well-circumscribed, inhomogeneous mass of low density, which can be explained by the following microscopic pattern: hypocellular areas (Antoni type B) adjacent to more cellular regions (Antoni type A) and cystic degeneration [4]. The radiologic findings for schwannoma are similar to those for ancient schwannoma, which is a rare variant of schwannoma first described by Ackerman and Taylor in 1951 [5].
Ancient schwannoma is usually located deep in the head and neck [6, 7], thorax [8], retroperitoneum [9, 10], pelvis [11], and extremities [12, 13] of elderly patients. It is characterized by degenerative changes typified by perivascular hyalinization, calcification, cystic necrosis, relative loss of Antoni type A tissue, and degenerative nuclei that may be misinterpreted as sarcomatous pleomorphisms [14]. Calcification is the usual degenerative change, but ossification, which was observed in our patient 7, is a rare degenerative variant [14, 15]. In our study, however, calcification and ossification could not be detected on radiologic examinations.
These degenerative changes are thought to be the result of the long-term progression of this tumor. Retroperitoneal ancient schwannoma is difficult to recognize if it has no clinical symptoms, or if it is located in the extremities with no other symptoms than local swelling, and patients tend to ignore the mass until it has finally reached an excessive size. For example, patient 1 had a tumor of the calf measuring 13.8 × 8.0 × 6.5 cm, which, to the best of our knowledge, is the largest reported ancient schwannoma in this location. However, the only complaint by the patient was of partial numbness on the side of the dorsum pedis, which he did not have medically examined until 10 years after first noticing the tumor.
Because it contains cystic areas, ancient schwannoma has been radiologically misdiagnosed as other tumor types, such as malignant fibrous histiocytoma, malignant peripheral nerve sheath tumor, liposarcoma, synovial sarcoma, or hemangiopericytoma. However, only a few reports have dealt with the radiologic features of ancient schwannoma because this tumor is so rarely encountered. Although Shultz et al. suggested that a diagnosis of ancient schwannoma should be considered when a patient presents with a hypervascular soft-tissue mass containing amorphous calcification on radiographs and cystic areas on MRI [13], calcification is not always visible on films [9, 12].
Our study suggests that MRI is the most useful technique for further evaluation of ancient schwannoma. Ordinary schwannomas show their peripheral region as a low-signalintensity area on T1-weighted images and a high-signal-intensity area on T2-weighted images—which correspond to the Antoni B area—and as low-to-intermediate-signal-intensity areas on T1- and T2-weighted images. Ordinary schwannomas are strongly enhanced by gadolinium contrast medium, which is also characteristic of the Antoni A area. On T1-weighted images, the tumors are isointense or slightly hyperintense relative to muscle, and a target pattern with a peripherally hyperintense rim and central low intensity on T2-weighted images has been reported for 52% of benign nerve sheath tumors (neurofibromas and schwannomas) [17]. This target pattern corresponds histologically to peripheral myxomatous tissue and central fibrocollagenous tissue; is absent in lesions with cystic, hemorrhagic, or necrotic degeneration; and is not visible in malignant peripheral nerve sheath tumors.
The ancient schwannoma in our series, however, showed a well-circumscribed complex cystic mass and different enhancement patterns. The circumference of the degenerative hematoma and cyst and the fibrous capsule of the tumor were enhanced. The Antoni type B area occupied most of the tumors, and the Antoni type A area had become smaller and was seen in the areas around the degenerative lesions. We therefore suspect that the Antoni type A areas had degenerated to hematomas or cysts.
Scintigraphy is also a helpful radiologic technique. A previous study found that schwannomas with the widest diameter (≥ 3 cm) were positive for technetium-99m dimercaptosuccinic acid and negative for 67Ga citrate [18]. Our patients with ancient schwannoma showed the same expression pattern, which indicates that a scintigram should be used to examine a large neurogenic tumor.
The preoperative differential diagnosis of a comparatively large soft-tissue tumor in an extremity that appears as a well-enhanced inhomogeneous tumor on MRI tends to identify it as malignant. Differentiation from a malignant tumor can be achieved by taking into account the characteristics of the clinical findings and radiologic features of ancient schwannoma. In this study, we made a tentative preoperative diagnosis of the tumors as schwannomas, except for patient 7. Although all the tumors had been diagnosed as ancient schwannoma, patient 7 was problematic before this study was performed because the tumor was large and had an indistinct margin, and so it was thought to be malignant.
In conclusion, the following points are important for differentiating ancient schwannoma and other tumors: The first is a mass with a long-term clinical course presenting with the symptoms of a neurogenic tumor. The second is a palpable mass with local pain and characteristics similar to Tinel's sign and distinct radiologic features that include an adjacent nerve visualized on sonography, a circumference of a degenerative area and fibrous tumor capsule enhanced on MRI, and positive accumulation seen on a bone scan but not on a gallium scan.

Footnote

Address correspondence to K. Isobe ([email protected]).

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Information & Authors

Information

Published In

American Journal of Roentgenology
Pages: 331 - 336
PubMed: 15269020

History

Submitted: November 3, 2003
Accepted: December 9, 2003

Authors

Affiliations

Kenichi Isobe
All authors: Department of Orthopedic Surgery, Shinshu University, School of Medicine, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan.
Tominaga Shimizu
All authors: Department of Orthopedic Surgery, Shinshu University, School of Medicine, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan.
Tsutomu Akahane
All authors: Department of Orthopedic Surgery, Shinshu University, School of Medicine, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan.
Hiroyuki Kato
All authors: Department of Orthopedic Surgery, Shinshu University, School of Medicine, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan.

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