Skeletal Radiol (1994) 23:593 595

Skeletal Radiology

Case report 872 Elizabeth Schultz, M.DJ, Melissa R. Sapan, M.D. 1, Barbara MeHeffey-Atkinson, M.D. 2, James B. Naidich, M.D. 1, Myron Arlen, M.D. 3

i Department of Radiology, North Shore University Hospital, Manhasset, New York, USA 2 Department of Pathology, North Shore University Hospital, Manhasset, New York, USA 3 Department of Surgery, North Shore University Hospital, Manhasset, New York, USA

Fig. 1. Frontal radiograph of the thigh reveals a soft tissue mass with amorphous calcification

Fig. 2. Arterial-phase image from femoral arteriogram. Highly vascular mass supplied from branches of the enlarged deep femoral artery

Fig. 3 A, B. Magnetic resonance imaging. A Axial Tl-weighted spin-echo sequence (TR650/TEll). An encapsulated soft tissue mass of heterogeneous intermediate signal intensity is demonstrated in the deep soft tissues on the medial aspect of the thigh. Vascular structures are seen in the periphery of the mass posteriorly. Foci of low signal intensity, suggestive of fluid, are also noted. The surrounding muscles are stretched over the mass and separated from the mass by fat. B Coronal T2-weighted spin-echo sequence (TR2500/TE80). The mass shows a heterogeneous pattern of increased signal intensity. Note the lobulated contour of the mass

Clinical information

A 64-year old woman presented with a 5-month history of an enlarging, pain- less mass located in the proximal por- tion of her left thigh. Significant medi- cal history included hypertension and carcinoma of the breast. On inspection, a large mass was visibly bulging from the medial portion of the thigh. No dis- coloration of the skin was present. Physical examination revealed a firm mass several centimeters in size within the adductor musculature. There were no additional clinical findings. Labora- tory results were normal.

Plain films revealed a soft tissue mass containing amorphous calcifica- tion (Fig. 1). Angiography, performed for surgical planning, demonstrated the hypervascular nature of the mass, with hypertrophy of the deep femoral artery and several of its branches (Fig. 2). Magnetic resonance imaging (MRI), undertaken to evaluate the full extent of the lesion, demonstrated a large, en- capsulated soft tissue mass of hetero- geneous signal intensity within the ad- ductor muscle group displacing and stretching the surrounding muscles (Fig. 3). The lobulated contour of the mass was best appreciated on images obtained in the coronal plane. On the axial images, vessels could be seen in the periphery of the mass posteriorly. The signal intensity of the tumor was predominantly isointense to that of muscle on the T l -we igh ted images; it was of heterogeneous increased signal intcnsity on the T2-weighted images. Cystic areas suggestive of necrosis, and loci of signal void, corresponding to calcification, were also demonstrat- ed. Due to the large size of the lesion, a clinical decision was made to excise rather than biopsy the mass.

Correspondence to: Elizabeth Schultz, M.D., Department of Radiology, North Shore University Hospital, 300 Community Drive, Manhasset, NY 11030, USA

�9 1994 International Skeletal Society

594 E. Schultz et al.: Case report 872

Diagnosis: "Ancient" schwannoma (degenerated neurilemoma)

The differential diagnosis includes malignant fibrous histiocytoma, lipo- sarcoma, synovial sarcoma, heman- giopericytoma, and metastatic tumor.

The surgical specimen consisted of a wide resection of skeletal mus- cle enveloping an ovoid, encapsulat- ed mass measuring 13.5 x 11.0 x 7.0 cm. Multiple cross-sections showed a glistening yellow-white parenchyma with several discreet cystic depres- sions and focal, dense calcification. Microscopically (Fig. 4), spindle- shaped, elongated focally hyperchro- matic Schwann cells were seen with- in a dense collagenized matrix. Con- fluent calcification was rather wide- spread. No nerve of origin was defi- nitely identified. Mitotic figues were rare. Although the typical Antoni A and Antoni B areas were inconspicu- ous in this hyalinlized schwannoma, ultrastructurally the classical redun- dant stacked appearance of the basil lamina wrapped around the schwann cells and the immunohistochemical reactivity for S-100 protein support- ed the diagnosis of degenerated schwannoma.

Malignant fibrous histiocytoma, the most commonly occurring pe- ripheral soft tissue sarcoma in adult-

hood, often presents as a painless mass in the lower extremity. Hyper- vascularity and lobulation of its con- tour are not unusual features of this tumor.

Liposarcoma may present with identical clinical findings. The two major sites of development are the retroperitoneum and the thigh. Calci- fication may be evident on plain films, particularly when the tumor contains osteogenic sarcomatous ele- ments. Pleomorphic liposarcomas may demonstrate hypervascularity on angiography [1].

A soft tissue mass of the extremi- ty demonstrating amorphous calcifi- cation always raises the possibility of a synovial sarcoma. Although the peak incidence of this tumor is in the third decade, in fact it can occur at almost any age. Both hypervascular- ity as seen on angiography, and cys- tic changes as demonstrated by MR have been reported.

Hemangiopericytoma is the more vascular of the peripheral soft tissue lesions. This rare mesenchymal tu- mor arises from the pericytes of Zimmermann and presents most commonly in the fifth and sixth de- cades of life. The most frequent sites of involvement are the lower extrem- ity, pelvis, and retroperitoneum. Ra- diographic evidence of calcification

Fig. 4. A thrombosed blood vessel shows calcification and perivascular hyalinization. The spindle-shaped, elongated Schwann cells with an abundant collagenized matrix are apparent. Two smaller hyalinized vessels are also in the field. These findings characterize a benign ancient schwannoma (H&E x 276)

occurs more often when the tumor is malignant than when it is benign. The most consistent radiographic finding is a tumor blush seen on an- giography. Areas of cystic change and necrosis have been described on computed tomography.

Given the patient's history of car- cinoma of the breast, the possibility of metastatic lesion must also be considered. Metastases to muscle are extremely rare. When they do occur, the primary neoplasm is generally re- nal cell carcinoma, malignant mela- noma, or bronchogenic carcinoma. The presence of amorphous calcifica- tion on plain films, however, tends to speak against a metastatic lesion.

Discussion

The usual peripheral schwannoma, also referred to as neurilemoma and neurinoma, is a slowly growing, be- nign, encapsulated tumor arising from the nerve sheath. Individuals most commonly affected are aged between 20 and 50 years. Schwa- nnomas generally occur as a solitary lesion located in the head or neck, mediastinum, retroperitoneum, pel- vis, or an extremity. Patients present with a soft tissue mass which may or may not be symptomatic. At times, pain can be elicited by percussing the area supplied by the affected nerve (Tinel's sign). The history of pa- tients' awareness of the mass varies from several weeks to several years. Malignant transformation is extreme- ly unusual [1, 2]. Treatment consists of surgical excision.

Plain film evaluation of classical schwannomas is generally unreveal- ing [3]. Angiographically, the major- ity of these tumors are hypovascular [4, 5]. Although malignant schwa- nnomas are more likely to be hyper- vascular than are their benign coun- terparts enough hypervascular benign schwannomas have been documented to preclude any meaningful conclu- sion regarding the benign or malig- nant nature of any schwannoma based on the degree of its neovascu- larity. Encasement of arteries by the tumor indicate that it is malignant [6]. The purpose of arteriography in this case and in general is to deter- mine preoperatively the degree of vascularity of the tumor and to ascer-

E. Schultz et al.: Case report 872 595

rain whether major arteries or veins are involved. MRI may yield similar information, making angiography su- perfluous in the future.

Findings reported in schwa- nnomas studied by MRI include the presence of a capsule and demonstra- tion of the nerve of origin at the pe- riphery of the tumoral mass [7]. As- sociated muscular atrophy has also been described [8]. Schwannomas are generally isointense to muscle on Tl-weighted spin echo images and markedly hyperintense on T2- weighted images. Both homogeneous and inhomogeneous signal patterns have been reported. A "target" pat- tern, consisting of a rim of bright sig- nal intensity surrounding a zone of lower signal intensity on T2-weight- ed images, has also been described. This pattern has been shown histo- logically to correspond to a peripher- al layer of myxomatous tissue sur- rounding a central zone of fibrocol- lagenous tissue [9]. The target pat- tern has also been reported with ne- urofibromas [9, 10].

The term "ancient schwannoma" is applied to schwannomas of long duration that demonstrate character- istics of degeneration on histological examination, i.e., calcification, peri- vascular hyalinization, and cystic de- generation. Nuclear hyperchroma- tism and pleomorphism are also evi- dent. In the case we present here, all of these features were present. An- cient schwannomas are extremely rare. Clinically, they are typically large and located in the deep soft tis- sues, as was our patient 's tumor.

Little information is available concerning the imaging characteris- tics of the ancient schwannoma. De- spite the fact that peripheral nerve sheath tumors are considered to be unrevealing on plain fihns, the tumor we report here demonstrated amor- phous calcification. To the best of our knowledge, the only previously reported peripheral schwannoma demonstrating calcification on plain films was one known to have been present for 10 years [11]. This tumor was probably an ancient schwa- nnoma as well. Even less informa- tion is available regarding the MRI features of ancient schwannomas. Two reported intrathoracic schwa- nnomas demonstrated fluid collec- tions on MRI that corresponded his-

tologically to cystic degeneration [12]. Quite possibly, these tumors were ancient schwannomas. A single ancient schwannoma reported in con- junction with nine classical schwa- nnomas studied by MRI was the only schwannoma in that series to demon- strate signal that was isointense to fat on T2-weighted images [7]. No ex- planation was given to account for this finding.

MRI of our patient 's tumor re- vealed a capsule. However, neither the nerve of origin, muscular atro- phy, or a "target" pattern were evi- dent. The lobulated contour of the tu- mor and heterogeneous pattern of signal intensity are suggestive of a malignant process. Several investiga- tive studies, however, have proven that these two MRI findings are not reliable indicators of malignancy. The contribution of MRI to the eval- uation of soft tissue masses lies in its unique ability to determine noninva- sively the extent of the tumoral mass and its relationship to neighboring structures and not in its rendering a histological diagnosis.

In summary, a case of an ancient schwannoma was presented. The rare occurence of this tumor has resulted in only a few reported cases with de- scriptions of its features on imaging. Our patient 's tumor, like one previ- ously reported case, demonstrated calcification on the plain film - a finding not associated with other his- tologic types of schwannomas. Angi- ography revealed the tumor to be hypervascular. Evaluation by MRI demonstrated a lobulated, encapsu- lated soft tissue mass containing sev- eral cystic areas that corresponded histologically to areas of necrosis. Hypertrophied blood vessels were seen in the periphery of the tumoral m a s s .

Too few ancient schwannomas have been reported to conclude whether or not radiographic evidence of soft tissue calcification is charac- teristic of this histologically distinc- tive subtype of schwannoma. Howev- er, since calcification is seen histo- logically as part of the degenerating process, its presence on plain films could be a feature of this tumor. Fur- thermore, the presence of cystic ar- eas on MRI is not surprising given the pathological changes that occur in this tumor.

We suggest that a diagnosis of an- cient schwannoma be considered when a patient presents with a hyper- vascular soft tissue mass containing amorphous calcification on plain films and cystic areas on MRI. De- spite the nonspecificity of these imaging findings, this point is rele- vant because each of these features suggests the presence of a malignant mass. Awareness of the possibility of a benign ancient schwannoma could obviate unnecessary radical surgery.

References

1. Enzinger FM, Weiss SW. Soft tissue tu- mors. 2nd edn. St. Louis: Mosby, 1988.

2. Dahl I. Ancient neurilemoma (schwa- nnoma). Acta Pathol Microbiol Scand [A] 1977; 85A: 812-818.

3. Enneking WF. Musculoskeletal tumor surgery. New York: Churchill Living- stone, 1983: 1273.

4. Berlin O, Stener B, Lindahl S, Irstam L, Lodding R Vascularization of pe- ripheral neurilemomas: angiographic, computed tomographic, and histologic studies. Skeletal Radiol 1986; 15: 275 283.

5. Stener B, ]~ngervall L, Nilsson L, Wickbom I. Angiographic and histolog- ic studies of the vascularization of pe- ripheral nerve tumors. Clin Orthop 1969; 66: 113-124.

6. Abrams HL. Abrams' angiography and interventional radiology, 3rd edn. Bos- ton: Little Brown, 1983: 1969.

7. Cerefolini E, Lnadi A, DeSantis G, Ma- iorana A, Canossi G, Romagnoli R. MR of benign peripheral nerve sheath tumors. J Comput Assist Tomogr 1991; 15: 593-597.

8. Stull MA, Moser RP, Kransdorf M J, Bogumill GR Nelson MC. Magnetic resonance appearance of peripheral nerve sheath tumors. Skeletal Radiol 1991; 20: 9-14.

9. Varma DGK, Moulopoulos A, Sara AS, Leeds N, Kumar R, Kim EE, Wallace S. MR imaging of extracranial nerve sheath. J Comput Assist Tomogr 1992; 16: 448-453.

10. Suh J-S, Abenoza P, Galloway HR, Ev- erson LI, Griffiths HJ. Peripheral (ex- tracranial) nerve tumors: correlation of MR imaging and histologic findings. Radiology 1992; 183: 341-346.

11. Nichols J, Tehranzadeh J. Case report 325: Benign neurilemoma in the poste- rior soft tissues of the right thigh. Skel- etal Radiol 1985; 14:136 140.

12. Sakai F, Sone S, Kiyono K, Maruyama A, Ueda H, Aoki J, Kawai T, Ishii K, Morimoto M, Hanuida M, Koizumi T. Intrathoracic neurogenic tumors: MR- pathologic correlation. AJR 1992; 159: 279-283.