immunohistochemical and ultrastructural study. Camillo Di Bella,1 Paolo Declich,1 Agnese Assi,1 Giovanna Cenacchi,4 Maria Sironi,1 Luigi Cozzi2 and Arturo.
Journal of Neuro-Oncology 35: 149–152, 1997. 1997 Kluwer Academic Publishers. Printed in the Netherlands.
Clinical Study
Melanotic schwannoma of the sympathetic ganglia: A histologic, immunohistochemical and ultrastructural study Camillo Di Bella,1 Paolo Declich,1 Agnese Assi,1 Giovanna Cenacchi,4 Maria Sironi,1 Luigi Cozzi2 and Arturo Griner3 Departments of 1Pathology, 2Radiology, and 3Neurosurgery, Legnano General Hospital, Legnano; 4Department of Electron Microscopy, S. Orsola-Malpighi Hospital, Bologna, Italy
Key words: Schwann’s cell, melanotic schwannoma, lumbar spine, immunohistochemistry, ultrastructure Summary We describe the case of a 46-year-old male patient who presented with pain in the left thigh, often accompanied by lumbar pain. These symptoms were sustained by a neoplasm, which was located in the sympathetic ganglia, at the level of the 3rd left lumbar spinal root and which was completely excised. Immunohistochemical positivity for S100, HMB45, and NSE antibodies suggested that the lesion was a melanotic schwannoma (MS), with both schwannian and melanocytic differentiations, the latter containing melanosomes at ultrastructural examination. Non-recurrence after 16 months of follow-up further supports our diagnosis of MS.
Introduction
Case report
Melanotic schwannoma (MS) is a neoplasm of neuroectodermal origin and is characterized by melanotic pigmentation in the cytoplasms of neoplastic Schwann’s cells. Melanin pigments are observed in other melanotic tumors, i.e. melanomas and melanocytomas, which have distinctive histological features. Most MS are located at the vertebral foramen or at the paravertebral sulcus, in connection with spinal nerves or, very rarely, with sympathetic ganglia [1–3]; occasionally MS can occur in soft tissues [5]. MS is generally observed in young adults, with incidence peaking in the 3rd and 4th decades [2]. Surgical resection is frequently curative, and recurrences are infrequent. Here we report a rare case of MS, which developed in the sympathetic ganglia, and which we studied with immunohistochemistry and electron microscopy.
A 46-year-old man was admitted to our institution for pain (duration, 1 month) in the anterior left thigh, associated with lumbar pain. Medical therapy was ineffective. Conventional X-ray examination, performed in another institution, showed an oval neoplasm of the left L3 root, measuring 1.5 × 1 cm. The growth was interpreted as a schwannoma. A preoperative CT scan confirmed the presence and the location of the neoplasm (Figure 1). At excision, the neoplasm, localized at the sensorial ganglion of the left L3 root, was completely removed. Clinical work-up (complete skin examination, rectosigmoidoscopy and ocular ultrasound examination) excluded the presence of other melanocytic lesions. The patient was alive and well, without recurrence, 16 months after surgery.
150 Results Macroscopic findings The resected specimen was a 1.5 × 1 cm well defined oval mass, with a smooth brownish external surface and a homogeneous, glistening cut surface. There were no apparent foci of necrosis and hemorrages.
Microscopic findings
Figure 1. TC- and T1-weighted RM images with contrast: the oval shaped intra and extraforaminal lesion (arrow), with poor contrast enhancement, is fused with the nervous root.
Materials and methods The specimen was fixed in 10% buffered formalin, cut at 4 µ, and stained with hematoxylin-eosin. Immunohistochemistry was performed with the ABC technique [4]. The following primary antisera were used: S100 protein (DAKO corporation, dilution 1 : 200), anti-melanoma HMB45 (BIOMEDA, prediluted), neuronal specific enolase (NSE) (DAKO, dilution 1 : 100), glial fibrillary acid protein (GFAP) (DAKO, dilution 1 : 800), synaptophysin SY38 (DAKO, dilution 1 : 10), and vimentin (DAKO, dilution 1 : 50). All antisera were incubated for 10 minutes at room temperature, as were secondary antibodies and ABC complex, both of which are available in kit (DAKO). The chromogen used was 3,3’diaminobenzidine (SIGMA). Small samples of the tumor were retrieved from paraffin block and processed for ultrastructural examination. After postfixation in 1% osmium tetroxide, the specimens were dehydrated in graded ethanol solution and embedded in Epon-Araldite resin. Thin sections (80 nm) were counterstained with uranyl acetate and lead citrate.
The neoplasm appeared to be largely composed of polygonal and spindle cells (Figure 2), with ill-defined cytoplasmic borders, nuclear pleomorphism and very few macronucleoli. No foci of necrosis were seen, and mitotic count was low (< 1X10HPF). We observed no whorled structures, nor any palisading, and/or ganglion cell-like differentiation. Many tumoral cells, as well as macrophages, showed large brown cytoplasmic (melanin) granules.
Immunohistochemical and ultrastructural findings Immunohistochemical stains showed positive reaction for S100 (Figure 3), HMB45 (Figure 4), NSE, and vimentin, whereas GFAP proved to be negative. Although performed on paraffin retrieved material, hence with poor preservation, ultrastructural examination revealed secondary lysosomes that contained melanin pigments; the melanosomes showed various stages of maturation, with a prevalence of stage IV (Figure 4 inset). Nuclei showed irregular profiles with deep indentations. Some cells showed abundant intermediate filaments in their cytoplasm. Basal membranes were absent.
Discussion MS generally derives either from the roots of spinal nerves, or occasionally from soft tissues [5]; localization at the sympathetic ganglia has rarely been described [1, 6]. The melanin pigmentation of the
151
with melanin pigment
152 tumor (in neoplastic cells, macrophages and stroma), raised the hypothesis of both a malignant (leptomeningeal?) melanoma, be it primary or metastatic, and of a malignant melanotic schwannoma. The absence of necrosis and the low mitotic count in our case argued against these two possibilities. Furthermore, from the clinical point of view, no primary malignant melanoma could be found. The presence of melanotic pigmentation may be the result either of synthesis by Schwann’s cells, or of exogenous phagocytosis. The hypothesis that Schwann’s cells synthetize melanin [7] has been confirmed by ultrastructural studies [5, 8, 9]. Electron microscopy has shown that neoplastic Schwann’s cells, in addition to pericellular basal membranes, may include premelanomsomes, melanosomes and melanin granules in various stages of maturation [10, 11]. Although the samples for the ultrastructural study were poorly preserved, we were able to identify predominantly stage IV melanosomes, which were suggestive more of a secondary uptake than of a primary production by neoplastic cells. The presence of these melanosomes supported the hypothesis of a Schwann’s cell origin, albeit that we did not observe pericellular basal membranes [5]. The phenotype of MS is characterized by reactivity for S100, HMB45 and NSE antibodies (as also observed in malignant melanomas) [12–14], and by negativity for GFAP [13, 15]. The biological behaviour of this neoplasia is unpredictable [16]. The absence of histological criteria for malignancy (high mitotic count, pleomorfism, necrosis) suggests a low aggressive potential. Hence, recurrence is probably related to an incomplete surgical removal. On the other hand the malignant variety of MS which has a high mytotic count may eventually metastasize to other organs. In conclusion, we believe that both immunohistochemistry and ultrastructural examination can contribute to diagnostic differentiation between MS and malignant melanoma, but the clinical history and the follow-up of the patient are of paramount importance for the exact definition of the behaviour of this neuroectodermal neoplasm. Sixteen months after surgery our patient was alive and well,
with no clinical and/or imaging evidence of recurrence, or of dissemination to distant sites.
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