Synovial sarcoma of nerve

Synovial Sarcoma of the Submaxillary Salivary Gland: A Rare Location and Challenging Diagnosis

Synovial sarcoma is a high-grade sarcoma. The periarticular region, deep soft tissues, and the extremities are where it is most frequently found. The head and neck regions are rarely affected and salivary gland localization is rather rare, especially the submaxillary gland. The process of diagnosis and therapeutic management remains challenging, particularly in cases with uncommon tumor locations where the establishment of a universal therapeutic consensus is complicated. Early diagnosis and a multidisciplinary approach can lead to success without locoregional recurrence or distant metastases.

Primary Synovial Sarcoma of the Scrotum

The report outlines a case of synovial sarcoma in the scrotal region. A 36-year-old male presented with a scrotal swelling. The lesion was completely resected, whereas the histopathologic examination revealed a spindle cell tumor. The tumor stained positive for pancytokeratin, AE1/AE3, epithelial membrane antigen (EMA), TLE-1, CD99, and BCL-2. The cytogenetic testing showed a chromosomal translocation in the SS18 gene at 18q11.2, consistent with the diagnosis of primary synovial sarcoma. A year later, the patient developed liver, vertebrae, and lung metastasis, which was treated with systemic chemotherapy. Treatment failed to improve the hepatic lesion that was then resected, while the spine and lung lesions were followed by radiotherapy. The patient is now alive and subject to an outstanding follow-up.

Synovial Sarcoma in the Extremity: Diversity of Imaging Features for Diagnosis and Prognosis

Synovial sarcomas are rare and highly aggressive soft-tissue sarcomas, primarily affecting adolescents and young adults aged 15-40 years. These tumors typically arise in the deep soft tissues, often near the large joints of the extremities. While the radiological features of these tumors are not definitely indicative, the presence of calcification in a soft-tissue mass (occurring in 30% of cases), adjacent to a joint, strongly suggests the diagnosis. Cross-sectional imaging characteristics play a crucial role in diagnosing synovial sarcomas. They often reveal significant characteristics such as multilobulation and pronounced heterogeneity (forming the "triple sign"), in addition to features like hemorrhage and fluid-fluid levels with septa (resulting in the "bowl of grapes" appearance). Nevertheless, the existence of non-aggressive features, such as gradual growth (with an average time to diagnosis of 2-4 years) and small size (initially measuring < 5 cm) with well-defined margins, can lead to an initial misclassification as a benign lesion. Larger size, older age, and higher tumor grade have been established as adverse predictive indicators for both local disease recurrence and the occurrence of metastasis. Recently, the prognostic importance of CT and MRI characteristics for synovial sarcomas was elucidated. These include factors like the absence of calcification, the presence of cystic components, hemorrhage, the bowl of grape sign, the triple sign, and intercompartmental extension. Wide surgical excision remains the established approach for definitive treatment. Gaining insight into and identifying the diverse range of presentations of synovial sarcomas, which correlate with the prognosis, might be helpful in achieving the optimal patient management.

The potential pitfalls of synovial sarcoma mimicking intraneural ganglion cyst: A case report and literature review

INTRODUCTION AND IMPORTANCE

Synovial sarcoma is a rare soft tissue sarcoma (STS) that accounts for 5-10 % of all STS. Synovial sarcoma of the peripheral nerve is very rare, with only 26 cases reported in the literature. Hence, this case report describes an unusual presentation of synovial sarcoma mimicking intraneural ganglion cysts and a literature review.

PRESENTATION OF CASE

We describe a 36-year-old female who presented to our clinic complaining of left leg pain for six years. MRI was done, which revealed a cystic lesion. With an impression of intraneural ganglion cyst versus nerve sheath tumor of the common peroneal nerve. The patient underwent exploration surgery and mass excision. The mass was sent for histopathology following excision, where the results indicated monophasic synovial sarcoma. An additional surgery, an epineurectomy of the common peroneal nerve and tumor bed excision, was followed by adjuvant chemotherapy with a Doxorubicin-based regimen. Following surgery, our patient's neurological symptoms improved.

CLINICAL DISCUSSION

The mainstay of treatment in synovial sarcoma is surgical excision with a Doxorubicin-based regimen of chemotherapy and/or radiotherapy based on tumor characteristics. Tumors smaller than 5 cm in MRI usually show homogenous enhancement and can be mistaken for benign tumors. Hence, a biopsy should be done before surgery to avoid misdiagnosis.

CONCLUSION

Even though it is extremely rare, synovial sarcoma of the lower extremity should be considered when a painful swelling of the lower leg is associated with a long duration of symptoms. Such lesions are best managed by surgical excision and postoperative chemotherapy.

Synovial sarcoma of the tibial nerve - case report of a rare tumor in a rare location requiring early diagnosis

BACKGROUND

We present the case of a patient with a rare synovial sarcoma (SS) of the tibial nerve. So far, only 4 cases of patients with SS originating from the tibial nerve have been described in the literature, and our patient is only the second patient whose limb was saved during treatment. Synovial sarcomas are malignant mesenchymal tumors, i.e., tumors arising from connective tissue. Synovial sarcomas account for 5-10% of all soft tissue sarcomas. However, the name synovial sarcoma is misleading, because the tumor does not originate from synovial cells, but rather from primitive mesenchymal cells. The name most likely originated from the localization around the large joints on the limbs, more often on the lower ones, in the area of the knee joints. We point out the aspects of correct and quick diagnosis and subsequent treatment, which has very important effect on the patient's prognosis. Primary less radical excision without prior biopsy verification leads to a higher risk of local recurrence, even if a proper reexcision was performed immediately after biopsy verification of the sarcoma.

CASE PRESENTATION

A woman born in 1949 began to suffer at the end of 2020 with escalating pain under the left inner ankle with a projection to the sole and fingers. Her personal, family work and social history were insignificant. After the initial neurological examination, the patient was sent for an ultrasound examination of the ankle, which showed a lobular mass measuring 50 × 22 × 16 mm and according magnetic resonance imaging, the finding appeared to be a suspicious neurinoma of the tibial nerve. The tumor was surgically excised, without prior biopsy verification: a 50 × 20 mm tumor was dissected in the distal part of the tarsal canal, which grew through the structure of the tibial nerve and in some places into the surrounding area and appeared intraoperatively as a neurofibroma. But histologically the tumor was classified as monophasic synovial sarcoma. The patient was indicated for a wide reexcision of the skin with the subcutaneous tissue of size 91 × 20 × 15 mm. Now the patient is being treated with external radiotherapy to the tumor bed and she is able to walk.

CONCLUSION

This report draws attention to a rare type of malignant nerve tumor, which both clinically and radiologically can mimic benign peripheral nerve sheath tumors. Synovial sarcoma should be considered in very painful resistances, typically located around the joints of the lower limbs, the growth of which can be slow. Because the size of the tumor is a negative prognostic factor, it is necessary to make a timely diagnosis using MR imaging and a biopsy with histological examination and to start treatment quickly. Surgical treatment should take place only after a biopsy with histological examination of the tumor so that it is sufficiently radical and does not have to undergo an additional reoperation, as happened in the case of our patient.

A Case of Poorly Differentiated Synovial Sarcoma Arising in a Nasal Cavity Radiation Field: An Unusual Tumor in an Unusual Location

Synovial sarcomas are high-grade soft tissue sarcomas of primitive mesenchymal origin which are defined by a pathognomonic t(X;18)(p11,q11) translocation, and which occur in pediatric and adult populations. Herein we report a case of a 33-year-old female with a history of nasopharyngeal carcinoma status post radiotherapy, presenting with a poorly differentiated synovial sarcoma of the nasal cavity arising in the radiation field. While the development of radiation-associated sarcoma is a known complication of radiotherapy, to date only 10 cases of synovial sarcoma have been reported to occur in previously irradiated tissues. Moreover, only 1 case of poorly differentiated synovial sarcoma involving the nasopharynx has been described.

Monophasic synovial sarcoma mimicking schwannoma: a case report of a rare peripheral nerve tumor and literature review

INTRODUCTION

Synovial sarcomas occurring as primary nerve tumors (SSPN) are rare and only 69 cases of SSPNs are reported in literature. Despite the little data available, SSPNs differ from other SSs in some distinctive aspects such as epidemiology, location, and early onset of symptoms. SSPN are consequently underdiagnosed and easily mistaken for benign or malignant peripheral nerve sheath tumors (PNST). Therefore, cytogenetic or molecular testing becomes essential in order to make a correct diagnosis. This article deals with an extremely rare case of monophasic SSPN of the posterior cords of the right brachial plexus. To our knowledge, this is only the tenth case of intraneural synovial sarcoma involving the brachial plexus.

CASE PRESENTATION

We report the case of a 64-year-old man, who came to our attention due to a slow-growing painful right axillary neoformation, approximately 25 mm in size. The patient did not show any neurological impairments. Ultrasonography and constrast MRI showed a heterogeneous mass arising from the posterior cord of the right brachial plexus, resembling a schwannoma. The patient underwent total resection of tumor and capsule. Histologically, a diagnosis of monophasic synovial sarcoma was made based on histologic features and the immunohistochemical profile.

CONCLUSIONS

We report a rare primary synovial sarcoma of the brachial plexus. Given its rarity, the diagnosis may be challenging and requires a core biopsy or the surgical specimen to permit immune-molecular analysis. Margin-free surgery is the mainstay of curative treatment, while chemo- or radiotherapy may have a role in advanced or margin-positive neoplasms.

Intraneural Synovial Sarcoma of the Median Nerve in a 15-Year-Old Male: A Case Report and Review of Literature

There have been 8 synovial sarcomas of the median nerve reported. We report a case of a 15-year-old male with synovial sarcoma of the right-hand median nerve. Patient presented with a 2-month history of enlarging mass at the base of the right thenar eminence associated with numbness in the median nerve distribution. Physical examination revealed a soft mass over the thenar eminence and paresthesia in the median nerve distribution. He underwent excision of the tumor, which revealed a well-encapsulated lesion encompassing the median nerve, involving the first, second, and radial aspect of the third web space as well as recurrent branches of the median nerve. Following excision of the tumor, a thorough metastatic workup was negative for metastatic disease. He was staged as III, T2b, N0, M0-poorly differentiated monophasic synovial sarcoma of the right median nerve. Postoperatively the patient was started on chemotherapy and radiation. Intraneural synovial sarcoma is extremely rare. Our case is the youngest with the longest follow-up. He is currently at a status of 3 years posttreatment with no signs of recurrence and excellent use of his right hand. This case is of particular interest due to the rarity of the disease along with this being the best outcome reported in the literature to-date.

S100-negative epithelioid malignant peripheral nerve sheath tumor with possible perineurial differentiation

Epithelioid malignant peripheral nerve sheath tumor (MPNST) is a rare subtype of MPNST composed of epithelioid cells with abundant cytoplasm. Currently, strong and diffuse immunostaining for S100 protein and SOX10 is generally regarded as a characteristic feature of epithelioid MPNST. However, malignant tumors with epithelioid morphology that arise from a peripheral nerve or a pre-existing benign nerve sheath tumor should be regarded as epithelioid MPNSTs when they do not show characteristic features that definitively lead to other specific diagnoses. Here, we describe 3 cases of epithelioid MPNST in the peripheral nerve or schwannoma that was negative for S100 protein and SOX10 expression. Instead, these tumors were positive for EMA, GLUT1, claudin 1, and cytokeratin to varying degrees, while all of them retained SMARCB1 and H3K27me3 by immunohistochemistry. EMA, GLUT1, and claudin 1 are known markers of perineurial cell differentiation; thus, they could possibly represent epithelioid MPNST with perineurial cell differentiation.

Diagnostic Pathology of Tumors of Peripheral Nerve

Neoplasms of the peripheral nervous system represent a heterogenous group with a wide spectrum of morphological features and biological potential. They range from benign and curable by complete excision (schwannoma and soft tissue perineurioma) to benign but potentially aggressive at the local level (plexiform neurofibroma) to the highly malignant (malignant peripheral nerve sheath tumors [MPNST]). In this review, we discuss the diagnostic and pathologic features of common peripheral nerve sheath tumors, particularly those that may be encountered in the intracranial compartment or in the spine and paraspinal region. The discussion will cover schwannoma, neurofibroma, atypical neurofibromatous neoplasms of uncertain biological potential, intraneural and soft tissue perineurioma, hybrid nerve sheath tumors, MPNST, and the recently renamed enigmatic tumor, malignant melanotic nerve sheath tumor, formerly referred to as melanotic schwannoma. We also discuss the diagnostic relevance of these neoplasms to specific genetic and familial syndromes of nerve, including neurofibromatosis 1, neurofibromatosis 2, and schwannomatosis. In addition, we discuss updates in our understanding of the molecular alterations that represent key drivers of these neoplasms, including neurofibromatosis type 1 and type 2, SMARCB1, LZTR1, and PRKAR1A loss, as well as the acquisition of CDKN2A/B mutations and alterations in the polycomb repressor complex members (SUZ12 and EED) in the malignant progression to MPNST. In summary, this review covers practical aspects of pathologic diagnosis with updates relevant to neurosurgical practice.

Imaging of non-neurogenic peripheral nerve malignancy-a case series and systematic review

OBJECTIVE

To evaluate the frequency, clinico-pathologic and imaging features of malignant tumors in peripheral nerves which are of non-neurogenic origin (non-neurogenic peripheral nerve malignancy-PNM).

MATERIALS AND METHODS

We retrospectively reviewed our pathology database for malignant peripheral nerve tumors from 07/2014-07/2019 and performed a systematic review. Exclusion criteria were malignant peripheral nerve sheath tumor (MPNST). Clinico-pathologic and imaging features, apparent diffusion coefficient (ADC_min), and standard uptake values (SUV_max) are reported.

RESULTS

After exclusion of all neurogenic tumors (benign = 196, MPNST = 57), our search yielded 19 non-neurogenic PNMs (7%, n = 19/272), due to primary intraneural malignancy (16%, n = 3/19) and secondary perineural invasion from an adjacent malignancy (16%, n = 3/19) or metastatic disease (63%, n = 12/19). Non-neurogenic PNMs were located in the lumbosacral plexus/sciatic nerves (47%, n = 9/19), brachial plexus (32%, n = 6/19), femoral nerve (5%, n = 1/19), tibial nerve (5%, n = 1/19), ulnar nerve (5%, n = 1/19), and radial nerve (5%, n = 1/19). On MRI (n = 14/19), non-neurogenic PNM tended to be small (< 5 cm, n = 10/14), isointense to muscle on T1-W (n = 14/14), hyperintense on T2-WI (n = 12/14), with enhancement (n = 12/12), low ADC_min (0.5-0.7 × 10-3 mm²/s), and variable metabolic activity (SUV_max range 2.1-13.1). A target sign was absent (n = 14/14) and fascicular sign was rarely present (n = 3/14). Systematic review revealed 89 cases of non-neurogenic PNM.

CONCLUSION

Non-neurogenic PNMs account for 7% of PNT in our series and occur due to metastases and primary intraneural malignancy. Although non-neurogenic PNMs exhibit a non-specific MRI appearance, they lack typical signs of neurogenic tumors such as the target sign. Quantitative imaging features identified by DWI (low ADC) and F¹⁸-FDG PET/CT (high SUV) may be helpful clues to the diagnosis.

Synovial Sarcoma of the Nerve-Clinical and Pathological Features: Case Series and Systematic Review

BACKGROUND

Synovial sarcoma of the nerve is a rare entity with several cases and case series reported in the literature. Despite an improved understanding of the biology, the clinical course is difficult to predict.

OBJECTIVE

To compile a series of patients with synovial sarcoma of the peripheral nerve (SSPN) and assess clinical and pathological factors and their contribution to survival and recurrence.

METHODS

Cases from 2 institutions collected in patients undergoing surgical intervention for SSPN. Systematic review including PubMed and Scopus databases were searched for related articles published from 1970 to December 2018. Eligibility criteria: (1) case reports or case series reporting on SSPN, (2) clinical course and/or pathological features of the tumor reported, and (3) articles published in English.

RESULTS

From patients treated at our institutions (13) the average follow-up period was 3.2 yr. Tumor recurrence was seen in 4 cases and death in 3. Systematic review of the literature yielded 44 additional cases with an average follow-up period of 3.6 yr. From pooled data, there were 10 recurrences and 7 deaths (20% and 14%, respectively). Adjuvant treatment used in 62.5% of cases. Immunohistochemical markers used in diagnosis varied widely; the most common are the following: Epithelial membrane antigen (EMA), cytokeratin, vimentin, cluster of differentiation (CD34), and transducin-like enhancer of split 1 (TLE1). Statistical analysis illustrated tumor size and use of chemotherapy to be negative predictors of survival. No other factors, clinically or from pathologist review, were correlated with recurrence or survival.

CONCLUSION

By combining cases from our institution with historical data and performing statistical analysis we show correlation between tumor size and death.

Intraneural synovial sarcoma of the tibial nerve

Synovial sarcomas are malignant soft tissue tumors that carry a metastatic potential and portend poor prognoses. We report a very rare synovial sarcoma arising from the tibial nerve and describe its successful treatment including limb preservation. To the best of our knowledge, this is the 40th reported incident of intraneural synovial sarcoma, and only the fourth arising from the tibial nerve. Extensive resection of synovial sarcoma arising in the popliteal region is difficult, particularly when limb preservation is desired. Ours is the first reported patient treated for tibial nerve-derived synovial sarcoma whose limbs were preserved.

Low-grade fibromyxoid sarcoma arising within the median nerve

We report a case of low-grade fibromyxoid sarcoma arising within the median nerve. A 31-year-old woman presented with symptoms of carpal tunnel syndrome and an enlarging mass in her right palm over 1 year. MRI demonstrated a mass associated with the right median nerve with solid and cystic components. At surgery, the mass was located within the epineurium, could be bluntly dissected from the nerve fascicles, and was suspected to be a schwannoma. A 3.4 cm, tan-pink, glistening, smooth, homogenous mass was submitted to pathology. Microscopically, the tumor was a solid and cystic circumscribed nodule with a dense fibrous pseudocapsule. The tumor cells were uniformly bland and spindle-shaped, with small, hyperchromatic oval nuclei and were embedded in an alternating fibrous and myxoid stroma with a prominent curvilinear vasculature and perivascular sclerosis. The differential diagnosis for this lesion included myxoid neurofibroma, schwannoma, soft tissue perineurioma, low-grade malignant peripheral nerve sheath tumor and low-grade fibromyxoid sarcoma. The tumor cells expressed MUC4, GLUT-1, and vimentin and were negative for S-100 protein, epithelial membrane antigen, smooth muscle actin, desmin, claudin-1, neurofilament and SOX10. Fluorescence in situ hybridization, with a break-apart probe strategy, demonstrated FUS rearrangement, consistent in this morphological context with the low-grade fibromyxoid sarcoma-associated FUS-CREB3L2 or FUS-CREB3L1 fusions. Low-grade fibromyxoid sarcoma is exceptionally rare in the peripheral nerve, with only a single previously reported case. Nonetheless, as our case illustrates, this entity must be included in the differential diagnosis of unusual intraneural mesenchymal tumors. As in all other locations, intraneural low-grade fibromyxoid sarcomas should be excised with negative margins. Patients with this disease require long-term clinical follow-up, given this tumor's propensity for very late distant metastases to the lungs and other sites.

Synovial sarcoma mimicking benign peripheral nerve sheath tumor

OBJECTIVE

To assess the radiographic and clinicopathologic features of synovial sarcoma of the nerve that were clinically or radiologically interpreted as benign peripheral nerve sheath tumor.

MATERIALS AND METHODS

Five patients with synovial sarcoma arising from the peripheral nerve and interpreted clinically and radiologically as peripheral nerve sheath tumors were identified. Clinicopathologic and imaging features were evaluated.

RESULTS

There were three females and two males, ranging in age from 28 to 50 (mean 35.8) years. Most patients (4/5) complained of a mass, discomfort or pain. MR images demonstrated a heterogeneous, enhancing, soft tissue mass contiguous with the neurovascular bundle. On histologic examination, most tumors were monophasic synovial sarcoma (4/5). At the time of surgery, all tumors were noted to arise along or within a peripheral nerve. All patients were alive with no evidence of disease with median follow-up of 44 (range 32-237) months. For comparison, approximately 775 benign peripheral nerve sheath tumors of the extremities were identified during the same time period.

CONCLUSIONS

Primary synovial sarcoma of the nerve can mimic peripheral nerve sheath tumors clinically and on imaging and should be included in the differential diagnosis for tumors arising from peripheral nerves.

Synovial Sarcoma of Peripheral Nerves: Analysis of 15 Cases

Synovial sarcoma of peripheral nerve (SSPN) is rare with only 26 cases reported in English. SSPN is often mistaken for a benign or malignant peripheral nerve sheath tumor (PNST) by clinicians and pathologists. Fifteen cases of SSPN were retrieved from the pathology files of 3 institutions. All tumors arose in a nerve based on imaging and/or operative findings and the diagnoses were histologically confirmed. Neuropathic symptoms predominated in 11 women and 4 men, 19- to 62-year-old (median, 39 years) with tumors involving the ulnar (5), median (3), peroneal (3) or sciatic (2) nerve, or the L4 or T1 nerve root (2). Tumor sizes ranged from 2 to 13 cm (median, 3.8 cm). The leading clinical diagnosis was PNST (9). Treatment was surgical (14) supplemented with radiation therapy (8) and chemotherapy (6). Fourteen tumors were monophasic and 1 was biphasic; 4 had poorly differentiated (PD) foci (1 rhabdoid). Diagnoses in 12 cases were verified by fluorescence in situ hybridization, reverse transcription polymerase chain reaction or both methods. Follow-up in 14 patients (median, 32 mo) revealed that 2/4 patients with PD tumors died with pulmonary metastases; another was alive with no current evidence of disease (NED) following 2 local recurrences, while the fourth had NED. In contrast, 9/10 patients without PD tumors were alive (7 NED) and 1 died at 12 months with pulmonary infiltrates. SSPN is under-recognized clinically and histologically as it mimics benign and malignant PNST. Molecular analysis is recommended to confirm the diagnosis. PD foci, including rhabdoid areas, may portend a worse outcome, similar to non-neural-based tumors.

Malignant Peripheral Nerve Sheath Tumor With Divergent Glandular Differentiation

Malignant peripheral nerve sheath tumors (MPNST) are soft tissue neoplasms with evidence of nerve sheath differentiation. They usually arise from peripheral nerves or from preexisting benign nerve sheath neoplasms, often in patients with neurofibromatosis type 1 (NF1). The histologic diagnosis of MPNST is challenging as their morphology is highly variable, and there has been a lack of routine diagnostic immunohistochemical markers and specific genetic aberrations. Although divergent differentiation is well documented in MPNST, it is most frequently toward mesenchymal elements. Differentiation toward epithelial elements is very rare, and we illustrate a case of MPNST with glandular differentiation, comprising prominent well-formed glands, with a brief discussion of biphasic (spindle and glandular) neoplasms in the differential diagnosis. An index of suspicion for MPNST is necessary, due to the differing management from tumors in its differential diagnosis, and because of the potential for therapies toward molecular targets in future.

BCOR upregulation in a poorly differentiated synovial sarcoma with SS18L1-SSX1 fusion-A pathologic and molecular pitfall

The diagnosis of poorly differentiated synovial sarcoma (PD-SS) may be challenging due to overlapping morphologic features with other undifferentiated round cell sarcomas (URCS). Particularly relevant is the histologic overlap and shared BCOR overexpression between a subset of SS and URCS with various BCOR genetic abnormalities. Here, we report a case of PD-SS lacking the canonical SS18-SSX gene fusion, but showing strong BCOR immunoreactivity and BCOR gene abnormalities by FISH, which were misinterpreted as a URCS with BCOR gene rearrangements. The tumor had an unusual clinical presentation arising as an intraneural tumor in the ankle of a 29-year-old female. The tumor displayed a mixture of fascicular spindle cells and undifferentiated round cell components. FISH studies showed no SS18 gene abnormality; however, RNA sequencing identified a fusion transcript involving SS18L1 (a paralog gene of SS18 at 20q13.33) and SSX1. Further FISH testing validated rearrangements in SSX1 and SS18L1 genes, in addition to complex structural abnormalities of the Xp11.22-4 region. This is the second reported SS case harboring an SS18L1-SSX1 alternative fusion variant, similarly occurring in association with a large nerve. The lack of SS18 gene rearrangements by FISH corroborated with the BCOR overexpression at both mRNA and protein level may result in diagnostic pitfalls with URCS with BCOR gene abnormalities. Our results further suggest that BCOR upregulation is emerging as a common downstream pathway for SS with either typical SS18-SSX transcript or with rare fusion variants, such as SS18L1-SSX. © 2017 Wiley Periodicals, Inc.

Recurrent Primary Synovial Sarcoma of Median Nerve: A Case Report and Literature Review

We report a case of intraneural synovial sarcoma of the median nerve in a 39 year old lady with multiple local recurrences over thirteen years with no distant metastasis. The diagnosis of biphasic type of synovial sarcoma was confirmed by histopathology and immunohistochemistry. At the time of the fourth recurrence below elbow amputation was performed. This case is being reported for its rarity and propensity for local recurrence without distant metastasis.

Loss of H3K27me3 Expression Is a Highly Sensitive Marker for Sporadic and Radiation-induced MPNST

Most malignant peripheral nerve sheath tumors (MPNSTs) exhibit combined inactivation of NF1, CDKN2A, and polycomb repressive complex 2 component genes (Embryonic Ectoderm Development [EED] and Suppressor of Zeste 12 [SUZ12]). Mutations in EED and SUZ12 induce loss of trimethylation at lysine 27 of histone 3 (H3K27me3), with subsequent aberrant transcriptional activation of polycomb repressive complex 2-repressed homeobox master regulators. These findings prompted us to investigate the performance of an anti-H3K27me3 monoclonal antibody clone C36B11 as an immunohistochemical marker for MPNSTs. We assessed the C36B11 reactivity pattern in a pathologically and genetically well-characterized cohort of 68 MPNSTs, spanning various clinical presentations, such as type 1 neurofibromatosis (NF1), radiotherapy, and sporadic MPNSTs. We found that 69% (n=47) of all MPNSTs demonstrated loss of H3K27me3 expression, with 42 (61%) showing complete loss and 5 (7%) showing partial loss, whereas 31% (n=21) retained H3K27me3 expression. Among the NF1-related high-grade MPNSTs, 60% demonstrated loss of expression. In contrast, the majority of both sporadic (95%) and radiotherapy-related (91%) MPNSTs showed loss of H3K27me3 expression. Two of the 3 low-grade MPNSTs and all neurofibromas showed retained expression. Furthermore, all 5 epithelioid MPNSTs retained H3K27me3 labeling. The specificity of H3K27me3 loss as a marker for MPNSTs was studied by testing a large spectrum of lesions included in MPNST differential diagnosis, such as spindle/desmoplastic melanomas, synovial sarcomas, myoepithelial tumors, and other mesenchymal neoplasms, all of which retained expression of H3K27me3. We conclude that immunohistochemical analysis of H3K27me3 has good sensitivity and robust specificity for the diagnosis of MPNST, particularly outside of NF1 clinical history, which represents the most challenging diagnostic setting.

Intraneural Extension of Synovial Sarcoma: Exceptional, or Simply Underrecognized?

Intraneural extension of soft tissue sarcomas is uncommon; it is most frequently seen in malignant peripheral nerve sheath tumor, but its occurrence is exceptional in synovial sarcoma. We describe a case arising extraneurally within the deep soft tissues of the forearm, which recurred and resulted in above-elbow amputation, revealing an unexpected finding of diffuse intraneural extension of tumor within a macroscopically normal major nerve. Despite macroscopic and microscopically clear soft tissue margins, the neoplasm had "traveled" a significant distance intraneurally to involve the neural resection margin. This feature does not appear to have been described before; it highlights the issue of whether intraneural spread of synovial sarcoma might have been previously underrecognized, and we discuss briefly some practical implications.

Synovial sarcoma: defining features and diagnostic evolution

Synovial sarcoma (SS) is a malignant mesenchymal neoplasm with variable epithelial differentiation, with a propensity to occur in young adults and which can arise at almost any site. It is generally viewed and treated as a high-grade sarcoma. As one of the first sarcomas to be defined by the presence of a specific chromosomal translocation leading to the production of the SS18-SSX fusion oncogene, it is perhaps the archetypal "translocation-associated sarcoma," and its translocation remains unique to this tumor type. Synovial sarcoma has a variety of morphologic patterns, but its chief forms are the classic biphasic pattern, of glandular or solid epithelial structures with monomorphic spindle cells and the monophasic pattern, of fascicles of spindle cells with only immunohistochemical or ultrastructural evidence of epithelial differentiation. However, there is significant morphologic heterogeneity and overlap with a variety of other neoplasms, which can cause diagnostic challenge, particularly as the immunoprofile is varied, SS18-SSX is not detected in 100% of SSs, and they may occur at unusual sites. Correct diagnosis is clinically important, due to the relative chemosensitivity of SS in relation to other sarcomas, for prognostication and because of the potential for treatment with specific targeted therapies in the near future. We review SS, with emphasis on the diagnostic spectrum, recent immunohistochemical and genetic findings, and the differential diagnosis.

Clinical Neuropathology practice guide 6-2013: morphology and an appropriate immunohistochemical screening panel aid in the identification of synovial sarcoma by neuropathologists

Aims: Pathologists are under increasing pressure to accurately subclassify sarcomas, yet neuropathologists have limited collective experience with rare sarcoma types such as synovial sarcoma. We reviewed 9 synovial sarcomas affecting peripheral nerve diagnosed by neuropathologists and explored the morphologic and immunohistochemical differences between these and MPNST. Our goal was to make practical recommendations for neuropathologists regarding which spindle cell tumors affecting nerve should be sent for SYT-SSX testing. Methods: Clinical records and genetics were reviewed retrospectively and central pathology review of 9 synovial sarcomas and 6 MPNST included immunohistochemistry for SOX10, S100, BAF47, CK (lmw, pan, CK7, CK19), EMA, CD34, bcl2, CD99, and neurofilament. Results: Common synovial sarcoma sites were brachial plexus, spinal and femoral nerve, none were “intra-neural”, all had the SYT-SSX1 translocation, and 6/9 were monophasic with myxoid stroma and distinct collagen. Half of the monophasic synovial sarcomas expressed CK7, CK19 or panCK in a “rare positive cells pattern”, 8/9 (89%) expressed EMA, and all were SOX10 immunonegative with reduced but variable BAF47 expression. Conclusions: We recommend that upon encountering a cellular spindle cell tumor affecting nerve neuropathologists consider the following: 1) SYT-SSX testing should be performed on any case with morphology suspicious for monophasic synovial sarcoma including wiry or thick bands of collagen and relatively monomorphous nuclei; 2) neuropathologists should employ a screening immunohistochemical panel including one of CK7, panCK or CK19, plus EMA, S100 and SOX10, and 3) SYT-SSX testing should be performed on any spindle cell tumor with CK and/or EMA immunopositivity if SOX10 immunostaining is negative or only labels entrapped nerve elements.

Diagnostic utility of SOX10 to distinguish malignant peripheral nerve sheath tumor from synovial sarcoma, including intraneural synovial sarcoma

Synovial sarcoma and malignant peripheral nerve sheath tumor pose a significant diagnostic challenge given similar histomorphology. The distinction is further complicated by similar immunophenotype and especially by occasional synovial sarcomas that present as intraneural tumors. Although the presence of a t(X;18) rearrangement or expression of TLE1 can help confirm the diagnosis of synovial sarcoma, negative results for these tests are not diagnostic of malignant peripheral nerve sheath tumor. The SOX10 transcription factor, a putative marker of neural crest differentiation, may have diagnostic utility in this differential, but immunohistochemical data are limited. The goal of the present study was to determine the diagnostic utility of SOX10 to discriminate between synovial sarcoma and malignant peripheral nerve sheath tumor. Forty-eight cases of malignant peripheral nerve sheath tumor, all from patients with documented neurofibromatosis, and 97 cases of genetically confirmed synovial sarcoma, including 4 intraneural synovial sarcomas, were immunohistochemically stained for SOX10. The stain was scored for intensity and fraction of cells staining. Thirty-two of 48 malignant peripheral nerve sheath tumors (67%) were SOX10-positive. The majority of malignant peripheral nerve sheath tumors showed ≥2+ staining, but staining did not correlate with grade. By contrast, only 7/97 (7%) synovial sarcomas were SOX10-positive. Only three synovial sarcomas showed ≥2+ staining but, importantly, two of these were intraneural synovial sarcoma. Therefore, SOX10 is a specific (93%), albeit not very sensitive (67%), diagnostic marker to support a diagnosis of malignant peripheral nerve sheath tumor over synovial sarcoma. Furthermore, the stain needs to be interpreted with caution in intraneural tumors in order to avoid a potential diagnostic pitfall. It remains to be determined whether SOX10-positive cells in intraneural synovial sarcoma represent entrapped Schwann cells, synovial sarcoma cells or both.

Epithelioid sarcoma presenting as radial mononeuropathy: anatomical, magnetic resonance neurography and diffusion tensor imaging appearances

The authors report an unusual case of radial mononeuropathy caused by epithelioid sarcoma and describe the anatomical 3-Tesla MR neurography and the functional diffusion tensor imaging findings of the case, which were subsequently confirmed on surgical excision and histopathology.

Pediatric primitive intraneural synovial sarcoma of L-5 nerve root

Primitive intraneural synovial sarcomas are rare in children. The authors report the case of a 7-year-old girl affected by intraneural synovial sarcoma of a lumbar nerve root, the first such lesion in this location described in a child. The lesion mimicked a schwannoma clinically and radiologically. There was long-lasting leg pain in a radicular distribution, and a well-demarcated intraneural tumor was seen on MRI. On this basis, the first resection was conservative. However, histological examination documented a classic biphasic synovial sarcoma, which was confirmed by immunohistochemistry. After radical resection and adjuvant treatment, complete disease control was achieved and verified at 5-year follow-up. This case strongly suggests that early diagnosis and a multidisciplinary approach to this unusual spinal lesion are essential to achieving a better prognosis.

Pathology of peripheral nerve sheath tumors: diagnostic overview and update on selected diagnostic problems

Peripheral nerve sheath tumors are common neoplasms, with classic identifiable features, but on occasion, they are diagnostically challenging. Although well-defined subtypes of peripheral nerve sheath tumors were described early in the history of surgical pathology, controversies regarding the classification and grading of these tumors persist. Advances in molecular biology have provided new insights into the nature of the various peripheral nerve sheath tumors, and have begun to suggest novel targeted therapeutic approaches. In this review, we discuss current concepts and problematic areas in the pathology of peripheral nerve sheath tumors. Diagnostic criteria and differential diagnosis for the major categories of nerve sheath tumors are proposed, including neurofibroma, schwannoma, and perineurioma. Diagnostically challenging variants, including plexiform, cellular and melanotic schwannomas are highlighted. A subset of these affects the childhood population, and has historically been interpreted as malignant, although current evidence and outcome data suggest they represent benign entities. The growing current literature and the author's experience with difficult to classify borderline or "hybrid tumors" are discussed and illustrated. Some of these classification gray zones occur with frequency in the gastrointestinal tract, an anatomical compartment that must always be entertained when examining these neoplasms. Other growing recent areas of interest include the heterogeneous group of pseudoneoplastic lesions involving peripheral nerve composed of mature adipose tissue and/or skeletal muscle, such as the enigmatic neuromuscular choristoma. Malignant peripheral nerve sheath tumors (MPNST) represent a diagnostically controversial group; difficulties in grading and guidelines to separate "atypical neurofibroma" from MPNST are provided. There is an increasing literature of MPNST mimics which neuropathologists must be aware of, including synovial sarcoma and ossifying fibromyxoid tumor. Finally, we discuss entities that are lacking from the section on cranial and paraspinal nerves in the current WHO classification, and that may warrant inclusion in future classifications. In summary, although the diagnosis and classification of most conventional peripheral nerve sheath tumors are relatively straightforward for the experienced observer, yet borderline and difficult-to-classify neoplasms continue to be problematic. In the current review, we attempt to provide some useful guidelines for the surgical neuropathologist to help navigate these persistent, challenging problems.

Synovial Sarcoma of the Brachial Plexus

BACKGROUND AND IMPORTANCE:

Synovial sarcoma (SS) is a malignant soft-tissue tumor that rarely involves brachial plexus. The authors report a case of brachial plexus SS and review the relevant literature.

CLINICAL PRESENTATION:

A 53-year-old woman presented with gradually enlarging right subclavicular mass over 5 years associated with sharp aching pain radiating down toward the radial 3 fingers. On examination, she had a corresponding firm mass in the supraclavicular region with a positive Tinel sign. There was no objective neurological deficit. She underwent partial excision of this mass without any further adjuvant radiation or chemotherapy. Pathology was consistent with SS.

CONCLUSION:

Lack of any recurrence in this case 6 years after incomplete excision with no adjuvant therapy suggests slow clinical course in some of these sarcomas.