Sporadic Malignant Triton Tumor of Shoulder: a Case Report.

Background: Malignant triton tumors (MTT) are subtype of malignant peripheral nerve sheath tumor (MPNST) which develop from Schwan cells of peripheral nerves or within neurofibromas, and shows rhabdomyoblastic differentiation. It is a rare soft tissue tumor with poor prognosis. Objective: We report a case of Malignant Triton Tumor (MTT) arising in the right shoulder in a 46 year old male patient presented to our Musculoskeletal Oncology Clinic at Royal Rehabilitation center at King Hussein Medical Center during June 2018. Case presentation: The patient was complaining of an 8 months long progressive right shoulder pain and swelling at the posterior lateral area of the shoulder. As accurate diagnosis is crucial in such case, investigations that included x-rays and magnetic resonance imaging (MRI) demonstrated an soft tissue tumor involving the right shoulder area leading to the differential diagnosis of aggressive soft tissue tumor which laid down the plan of an open incisional biopsy to be reported histopathological as a case of Malignant Triton Tumor which is a very rare and aggressive sarcoma originates from the peripheral nerve sheaths as it is subtype of malignant peripheral nerve sheath tumors after which excision of the entire tumor with safety margin was performed and referred for adjuvant chemotherapy. Conclusion: The treatment of choice is radical tumor excision with wide margins followed by chemotherapy and /or radiotherapy to improve the 5 years survival rates.

Surgical management of large lower cranial nerves schwannomas: long term results of a less aggressive resection strategy.

In an effort to reduce the high morbidity and life-threatening complications after radical resection in large schwannoma surgery, alternative strategies of nontotal resections have emerged. To evaluate the long term clinical and oncological outcome after lower cranial nerves (LCN) schwannoma surgery operated on with a cranial nerve-sparing technique. Single center retrospective cohort study of 8 consecutive patients harboring LCN schwannomas operated on between March 2005 and October 2021. The mean LCN schwannoma diameter was 33 mm (range 26-51). Seven patients (87,5%) underwent a modified retrosigmoid approach. Three patients underwent gross total resection (37,5%), 3 had received neartotal resection (mean tumor residue 0,25 cc) and subtotal resection in 2 patients who presented with an extracranial extension of the tumor (mean tumor residue 2,44 cc). Both patients had received upfront additional GKRS. The three patients who presented with preoperative CN IX & X injuries recovered within 6 months after surgery. All of the five patients freed from any preoperative CNs IX & X symptoms experienced transient (80%) or definitive (one patient) disturbances after surgery. They all improved within 6 months but one who required long term gastrostomy feeding tube. This patient harbored a schwannoma originating from the glossopharyngeal nerve, which could not be anatomically preserved during surgery. Tumor control was achieved in 100% of cases with a mean follow-up of 91 months. LCN schwannomas could be surgically removed through a less aggressive non-radical resection strategy with acceptable functional results and excellent tumor control.

Cauda equina neuroendocrine tumor: a report of three cases and review of the literature with focus on differential diagnosis and postoperative management.

INTRODUCTION: Cauda equina neuroendocrine tumors (CENETs), previously described as cauda equina paragangliomas (PGLs) are rare and well-vascularized benign entities which can be often misdiagnosed with other intradural tumors more common in this anatomical site, such as ependymomas and neurinomas. We describe three cases of CENETs observed at our institution with particular focus on differential diagnosis and postoperative management. Since the lack of guidelines, we performed a literature review to identify factors that can predict recurrence and influence postoperative decision making. CASE REPORT AND LITERATURE REVIEW: We report on three patients, two of them presenting with a clinical history of lower back pain and sciatica. In all cases magnetic resonance imaging (MRI) of the lumbosacral spine with and without Gd-DTPA revealed an intradural lesion with strong contrast enhancement, first described as atypical ependymoma or schwannoma. A complete tumor resection was achieved in all cases, the histopathological diagnosis classified the tumors as CENETs. In our literature review, a total of 688 articles were screened and 162 patients were included. Patients demographic data, clinical symptoms, resection and recurrence were recorded. DISCUSSION: Differential diagnosis between CENETs and other more common tumors affecting cauda equina region, such as ependymomas or schwannomas (neurinomas), is still very challenging. Due to the lack of specific clinical or radiological characteristics, a correct preoperative diagnosis is almost impossible. With this paper we want to point out that CENETs must be considered in the differential diagnosis, most of all in case of entities with atypical radiological features. According to the literature, tumor recurrence after gross total resection is unlikely, while a long-term follow-up is recommended in case of subtotal resection or local aggressive behavior.

[Efficacy analysis of 23 cases of parapharyngeal space tumors removed by oral approach assisted by plasma and high-definition endoscopic system].

Objective:To explore the selection, efficacy and application of indications for parapharyngeal space tumor resection assisted by plasma and HD endoscopic system through oral approach. Methods:The clinical data of 23 patients with parapharyngeal space tumor resection assisted by plasma and HD endoscopic system were retrospectively analyzed in Department of Otolaryngology Head and Neck Surgery, the First Affiliated Hospital of Bengbu Medical University from January 2013 to June 2023. All cases were examined by high-resolution CT and MRI before operation, and some cases were examined by CTA or DSA. During the operation, the high definition nasal endoscopic recording system was assisted, and low temperature plasma knife was used in some cases. The follow-up time was from 3 to 115 months, and the median follow-up time was 45 months. Results:There were no deaths in this group. All patients had complete tumor resection. The maximum tumor diameter was as follows: （5.20±1.00） cm, the operation time was（128.70±46.67） min, and the average blood loss was（80.87±32.74） mL. One case of vascular smooth muscle tumor had more bleeding during the operation and was assisted by tracheotomy after operation. One case of nourishing vascular bleeding after operation of giant Schwannoma was investigated and hemostasis + external carotid artery ligation. Bleeding in the remaining cases was below 120 mL. Postoperative pathologies were all benign tumors, including 11 pleomorphic adenoma, 4 schwannoma, 2 base cell adenoma, 1 epidermoid cyst, 1 lymphatic cyst with infection, 1 angiomyoma, 1 solitary fibroma, 1 salivary gland cyst, and 1 tendon giant cell tumor. All patients were followed up. One patient originating from vagal schwannoma had 2-month vocal cord paralysis and 1 recurrence（recurrence of the skull base of schwannoma）. Conclusion:Oral approach assisted by plasma and high-definition endoscopic system is suitable for partial selective resection of benign tumors in parapharyngeal space, which has the advantages of less trauma and rapid recovery. When the tumor is blood-rich, suspected to be malignant, the top of the tumor is deep into the cranial base nerve canal,located outside the internal carotid artery, and larger than 6.0 cm considering pleomorphic adenoma, it is recommended to conduct an external open or auxiliary cervical small incision approach.

Sacral nerve root metastasis in a patient with lung carcinoma resembling neurinoma - a case report and literature review.

Intradural extramedullary metastases from systemic neoplasms are very rare, with an incidence ranging from 2% to 5% of all secondary spinal diseases. We present the case of a 53-year-old man diagnosed with lung adenocarcinoma with symptoms of severe back pain and tibial paresis. The magnetic resonance imaging (MRI) revealed an intradural lesion originating from the right S1 nerve root mimicking neurinoma. Total tumor removal was achieved via posterior midline approach. The histological examination was consistent with lung carcinoma metastasis. Due to the rarity of single nodular nerve root metastases, MRI images may be misinterpreted as nerve sheath tumors, such as schwannomas or neurofibromas. We performed a brief literature review outlining the mainstay of diagnosis, therapeutic approach, and the prognosis of these rare lesions.

Huge mediastinal ancient schwannoma causing acute respiratory failure: a case report.

Benign mediastinal tumor is usually asymptomatic and exhibits uncomplicated clinical course. Posterior mediastinal schwannoma is common, but a huge benign tumor causing acute respiratory failure due to mass effect is unusual. We present a patient who suffered from acute respiratory failure due to huge mediastinal mass effect and improved after en bloc surgical resection. A 56-year-old woman had no history of systemic disease, but experienced general discomfort and malaise for several months. She was referred to our emergency department after developing sudden respiratory failure. Intubation was performed with ventilator support and she was admitted to the intensive care unit. Chest radiograph and computed tomography showed a huge mass over the left pleural cavity causing left lung, heart, and mediastinal compression. After en bloc resection, she was weaned off the ventilator successfully and was discharged at 24 days after the operation. Postoperative outpatient follow-up showed no symptoms. Mediastinal ancient schwannoma is a rare posterior mediastinal benign tumor. However, mass effect might lead to lethal complications. En bloc resection is necessary for curative treatment.

Transcanal transpromontorial approach for vestibular schwannoma: experience of a single center.

BACKGROUND: The expanded transpromontorial transcanal approach (ExpTTA) represents a recent addition to the surgical approaches available for the treatment of vestibular schwannoma. An initial purely endoscopic version has been complemented by the use of the microscope and it is now one of the possible surgical options for small to medium-sized vestibular schwannomas with a predominantly intracanalar development. METHODS: This is a series of 54 patients who underwent microsurgical resection of sporadic, unilateral vestibular schwannoma, mainly Koos I-II with non-serviceable hearing, between January 2016 and January 2023 using the expanded transcanal transpromontorial approach. We describe the surgical technique, focusing on anatomical landmarks, and analyzing its advantages and shortcomings. Retrospective analysis of clinical outcomes is presented, including early and late complications. The mean follow-up was 46.7 months. RESULTS: We achieved gross total resection of the lesion in all cases, confirmed on the first follow-up MRI at least 6 months after each procedure. We did not record any intraoperative complication nor disease recurrence. We recorded two postoperative severe facial nerve palsies, one of which was permanent. No cases of disabling vertigo or imbalance were reported, and all patients reported full recovery of autonomy in daily activities. Three cases of otoliquorrhea were managed conservatively successfully. CONCLUSIONS: The transcanal transpromontorial approach combines the advantages of endoscopy with the possibilities provided by microsurgery. Our experience confirms its safety in terms of surgical complications and facial nerve outcome. This approach is amongst the treatment options for small-medium schwannomas in patients with impaired hearing, especially in young patients, ensuring radical resection, disease control, and minimal morbidity.

Differential diagnosis of rare adrenal cellular schwannomas: A case report.

BACKGROUND: Adrenal cellular schwannomas are exceptionally rare stromal tumors that are often misdiagnosed due to the lack of specific radiological, serological, or clinical features. In this report, we describe the differential diagnosis of a rare adrenal cellular schwannoma. METHODS: A 69-year-old man with a history of persistent hypertension, chronic kidney disease, hypertensive heart disease, and cardiac insufficiency was hospitalized due to bilateral lower extremity edema lasting for 3 months. Plain computed tomography at that time revealed a space-occupying lesion in the right adrenal gland. As serum levels of catecholamines, cortisol, and adrenocorticotropic hormone were within normal ranges, the edema was attributed to the chronic kidney disease and cardiac insufficiency, and the patient was referred to our hospital for surgical treatment. Contrast-enhanced computed tomography revealed heterogeneous enhancement in the adrenal mass indicating pheochromocytoma. An irregularly shaped 5 cm mass with a complete capsule in the right adrenal gland was laparoscopically resected. The postoperative histopathological diagnosis was adrenal cellular schwannoma. RESULTS: The postoperative course was unremarkable and the tumor did not recur during 5 years of follow-up. CONCLUSION: Adrenal cellular schwannoma is a very rare tumor that is extremely difficult to preoperatively diagnose. Histological and immunohistochemical analyses are required for differential diagnosis and confirmation. Cellular schwannomas can transform into malignant peripheral nerve sheath tumors, but not often. Consequently, regular postoperative follow-up is required for such patients, especially imaging.

[Minimally invasive removal of dumbbell shaped schwannomas with transforaminal lumbar fusion: a retrospective study with a minimum 3-year follow-up]. / Minimal'no invazivnoe udalenie ganteleobraznykh shvannom s transforaminal'nym poyasnichnym spondilodezom: retrospektivnoe issledovanie s minimal'nym 3-letnim katamnezom.

Currently, there are no standards in surgical treatment of dumbbell-shaped tumors of lumbo-foraminal region. OBJECTIVE: To evaluate the effectiveness and long-term results of minimally invasive resection of dumbbell-shaped lumbar schwannomas Eden type 2 and 3 combined with transforaminal lumbar interbody fusion and transpedicular stabilization. MATERIAL AND METHODS: A retrospective study included 13 patients (8 men and 5 women) with lumbar dumbbell tumors Eden type 2 and 3 who underwent minimally invasive facetectomy through posterolateral anatomical corridor, microsurgical tumor resection and MI TLIF. We analyzed intraoperative parameters, neurological functions (ASIA scale), clinical characteristics (ODI, SF-36), and complications. Resection quality and area of the multifidus muscle were assessed according to MRI data. All patients were followed-up throughout at least 3-year. RESULTS: Surgery time was 147 min, blood loss - 118 ml, hospital-stay - 7 days. Clinical parameters significantly improved in the follow-up period: ODI score decreased from 72 to 12 (p=0.004), SF-36 PCS increased from 26.24 to 48.51 (p=0.006) and MCS score increased from 29.13 to 53.68 (p=0.002). According to MRI data, no tumor recurrences and severe muscle atrophy (>30%) were observed after 3 years in all cases. Superficial wound infection occurred in 1 (7.7%) case. There were normal neurological functions (ASIA type E) in all patients. CONCLUSION: Minimally invasive facetectomy through posterolateral approach with MI TLIF technology can be used for safe and effective resection of dumbbell-shaped schwannomas Eden type 2 and 3.

Diagnostic Challenges and Imaging Considerations for Intraparotid Facial Nerve Schwannoma: A Case Report and Literature Review.

BACKGROUND A mass in the parotid gland usually indicates parotid gland neoplasia. Warthin tumors or pleomorphic adenomas are common differential diagnoses. Less frequently, other differential diagnoses and sites of origin are considered. Schwannomas are rare, benign tumors in the head and neck region. Even more rarely, these tumors occur in the intraparotid course of the facial nerve. In the following, we report about 2 patients in whom a mass in the right parotid gland was found incidentally during magnetic resonance imaging (MRI). CASE REPORT We reviewed data from the literature on intraparotid facial nerve schwannomas (IPFNS) and compared them with those from our cases. The focus was on data such as clinical history, clinical symptoms, electroneurography, and various imaging modalities, such as ultrasonography and MRI combined with diffusion-weighted imaging. CONCLUSIONS It is challenging to distinguish facial nerve schwannomas from other neoplasms. Patient's history, clinical symptoms, MRI examination with diffusion-weighted imaging, and high-resolution ultrasound imaging are decisive factors for diagnosis and should be performed when IPFNS is suspected. Diagnosis and therapy for IPFNS remain challenging. A wait-and-scan approach could be an option for patients with small tumors and good facial nerve function. On the other hand, patients with advanced tumors associated with limited facial nerve function can benefit from surgical approaches or stereotactic radiosurgery.

[Interdisciplinary Treatment Of Tumorous And Tumour-Like Lesions Of Peripheral Nerves]. / Interdisziplinäre Behandlung von Raumforderungen in Assoziation zu peripheren Nerven: Tumore und tumorähnliche Läsionen.

Tumorous or tumour-like lesions of peripheral nerves are generally rare, heterogeneous and challenging to diagnose and treat. They may become apparent by a palpable swelling (lump) near nerves, sensory and/or motor deficits, pain to touch or neuropathic pain. In 91% of cases, tumours are benign. The differentiation of entities and their characteristics as well as a function-preserving resection strategy are highly relevant. Misdiagnosis and inadequate treatment can lead to severe deficits and pain syndromes. Benign tumours include schwannomas and neurofibromas, which can occur sporadically but can also be associated with neurogenetic tumour disposition syndromes if they occur more frequently. Rarer benign nerve tumours include perineuriomas, lipomas, aggressive fibrosis (desmoid tumours), paragangliomas and haemangiomas. Ganglion cysts are described as tumour-like lesions. The association of nerve tumours with neurogenetic syndromes and the correct classification of potentially malignant lesions such as MPNST (malignant peripheral nerve sheath tumour) or intermediate stages such as ANNUBPs (atypical neurofibromatous neoplasms with unknown biological potential) pose particular challenges. Interdisciplinarity is highly relevant for clinical treatment and a correct diagnosis. The aim of our work is to provide an overview of the relevant entities, diagnostic evaluation and contemporary treatment strategies based on the current data situation and taking into account the recently published interdisciplinary AWMF S2k guideline "Diagnosis and Treatment of Peripheral Nerve Tumours".

Convolutional neural network-based magnetic resonance image differentiation of filum terminale ependymomas from schwannomas.

PURPOSE: Preoperative diagnosis of filum terminale ependymomas (FTEs) versus schwannomas is difficult but essential for surgical planning and prognostic assessment. With the advancement of deep-learning approaches based on convolutional neural networks (CNNs), the aim of this study was to determine whether CNN-based interpretation of magnetic resonance (MR) images of these two tumours could be achieved. METHODS: Contrast-enhanced MRI data from 50 patients with primary FTE and 50 schwannomas in the lumbosacral spinal canal were retrospectively collected and used as training and internal validation datasets. The diagnostic accuracy of MRI was determined by consistency with postoperative histopathological examination. T1-weighted (T1-WI), T2-weighted (T2-WI) and contrast-enhanced T1-weighted (CE-T1) MR images of the sagittal plane containing the tumour mass were selected for analysis. For each sequence, patient MRI data were randomly allocated to 5 groups that further underwent fivefold cross-validation to evaluate the diagnostic efficacy of the CNN models. An additional 34 pairs of cases were used as an external test dataset to validate the CNN classifiers. RESULTS: After comparing multiple backbone CNN models, we developed a diagnostic system using Inception-v3. In the external test dataset, the per-examination combined sensitivities were 0.78 (0.71-0.84, 95% CI) based on T1-weighted images, 0.79 (0.72-0.84, 95% CI) for T2-weighted images, 0.88 (0.83-0.92, 95% CI) for CE-T1 images, and 0.88 (0.83-0.92, 95% CI) for all weighted images. The combined specificities were 0.72 based on T1-WI (0.66-0.78, 95% CI), 0.84 (0.78-0.89, 95% CI) based on T2-WI, 0.74 (0.67-0.80, 95% CI) for CE-T1, and 0.81 (0.76-0.86, 95% CI) for all weighted images. After all three MRI modalities were merged, the receiver operating characteristic (ROC) curve was calculated, and the area under the curve (AUC) was 0.93, with an accuracy of 0.87. CONCLUSIONS: CNN based MRI analysis has the potential to accurately differentiate ependymomas from schwannomas in the lumbar segment.

[Surgically Resected Cases of Mediastinal Ganglioneuroma Detected in Adults].

A ganglioneuroma is a rare, benign, neurogenic tumor originating from the sympathetic ganglion. Mediastinal ganglioneuroma are mostly detected in children, typically around 10 years of age, and are rarely identified in adults. Herein, we report two surgically resected cases of mediastinal ganglioneuroma in adults. In Case 1, a 53-year-old man, without any symptom, underwent a computed tomography, revealing a 3.2 cm well-defined paravertebral superior mediastinal tumor with long craniocaudal axis. In case 2, a 29-year-old woman presented with newly-developed ptosis and a history of left-sided facial hypohidrosis since the age of 10. Chest computed tomography (CT) revealed a 7.8 cm well-defined paravertebral superior mediastinal tumor with long craniocaudal axis. Both patients were initially suspected to have neurogenic tumors, particularly schwannomas. They underwent mediastinal tumor resections, requiring sympathetic nerve trunk dissection. Pathological examination confirmed the diagnosis of ganglioneuromas in both cases. Mediastinal ganglioneuroma must be differentiated from schwannoma, the most common neurogenic tumor in adults. Unlike schwannoma, ganglioneuroma cannot be enucleated, therefore attention should be focused on complications associated with sympathetic nerve trunk dissection, such as Horner's syndrome, hyperhidrosis, and arrhythmia. Identifying this rare entity and its characteristic imaging aids in preoperative differentiation, strategizing surgical approaches, and predicting complications.

Lumbar clear cell meningioma mimicking schwannoma 7 years after resection of the same type of intracranial tumor: a case report.

BACKGROUND: Meningioma is the second most common intradural extramedullary tumor, following schwannoma. Meningioma is primarily categorized as benign World Health Organization grade 1, but clear cell meningioma is grade 2 of the intermediate malignant category. Clear cell meningiomas are rare, accounting for less than 1% of all meningioma tumors. There is no previous report of multiple intraspinal clear cell meningiomas without dural attachment. CASE PRESENTATION: A 27-year-old Asian male patient presented with lower right extremity pain, and had undergone tumor resection for intracranial clear cell meningioma 7 years previously, with re-resection and radiotherapy for local tumor recurrence at our hospital's department of neurosurgery being carried out 4 years previously. No recurrence was observed since then. Preoperative lumbar magnetic resonance imaging showed two tumors at the L1 and L4 levels, both mimicking schwannoma with well-defined margins, no dural tail sign and homogeneous internal contrast. Intraoperative findings on tumor resection showed two tumors contiguous with the right L2 and L5 roots, which were not attached to the dura mater, similar to a schwannoma. After gross total resection, the postoperative pathology revealed no nuclear SMARCE1 antibody staining. The patient was diagnosed with clear cell meningioma. The patient's postoperative course went well, with no symptoms of nerve dropout and no recurrence 2 years after surgery. In this case, both lumbar lesions were well demarcated and spherical in shape, occurring with single roots. Tumor characteristics suggested a primary rather than a metastatic lesion. Clear cell meningioma is characterized by a SMARCE1 mutation and is different from other types of meningiomas. CONCLUSION: To the best of our knowledge, this is the first report of multiple intraspinal clear cell meningiomas without dural attachment at the lumbar spine after resection of intracranial clear cell meningioma. We speculate that the two tumors were de novo lesions on the basis of the features of the tumors, although they were detected 7 years after the resection of intracranial clear cell meningioma.

Benign cervical schwannoma with tracheal invasion.

Schwannomas commonly develop in the cervical region, 25% - 45% of cases are diagnosed in this anatomical region. Tracheal neurogenic tumors are exceedingly rare and can be misdiagnosed as invasive thyroid carcinomas or other infiltrating malignancies when present at the level of the thyroid gland. Here, we present a case of synchronous benign cervical schwannoma with tracheal invasion and papillary thyroid carcinoma in a patient who was initially hospitalized for COVID-19. The patient presented with dyspnea that was later found to be caused by tracheal extension of a cervical tumor. Surgical excision was performed, and the surgical team proceeded with segmental tracheal resection, removal of the cervical mass, and total thyroidectomy. The specimen was sent for pathological analysis, which revealed synchronous findings of a benign cervical schwannoma with tracheal invasion and papillary thyroid carcinoma. The literature on this subject, together with the present case report, suggests that neurogenic tumors should be included in the differential diagnosis of obstructing tracheal cervical masses. Surgical excision is the first-line of treatment for benign cervical schwannomas.

O-arm guided minimally invasive resection of intrathoracic epidural schwannoma: how I do it.

BACKGROUND: Schwannomas are the most common intrathoracic neurogenic tumors. In the past, they were often treated by traditional open surgery. Video-assisted thoracic surgery (VATS) has also been used for some large tumors. Recently, minimally invasive posterior neurosurgical technique provides a new option for some of these tumors. METHOD: Here, we describe the specific steps involved in the O-arm guided minimally invasive removal of intrathoracic epidural schwannoma, as well as its advantages and limitations. CONCLUSION: O-arm guided minimally invasive resection of intrathoracic epidural schwannoma is safe and effective and causes little damage.

Transmaxillary approach for resection of maxillary division trigeminal schwannoma at foramen rotundum.

BACKGROUND: The foramen rotundum and anterior cavernous sinus have traditionally been accessed by transcranial approaches that are limited by the high density of critical neurovascular structures. The transmaxillary approach provides an entirely extradural route to the foramen rotundum and anterior cavernous sinus. METHOD: This patient with neurofibromatosis and facial pain with trigeminal schwannoma at the foramen rotundum was successfully treated by transmaxillary resection of the tumor. This approach allowed for a direct extradural access to the pathology, with bony decompression and tumor resection, avoiding transcranial routes. CONCLUSION: The transmaxillary approach provides a safe and entirely extradural corridor to access smaller localized skull base lesions at and surrounding the cavernous sinus.

Intramuscular Hybrid Nerve Sheath Tumor of the Thigh: Case Report and Literature Review.

BACKGROUND/AIM: Hybrid nerve sheath tumor (HNST) is a benign peripheral nerve sheath tumor with combined features of more than one histological type, such as schwannoma, neurofibroma, and perineurioma. It remains under-recognized in routine clinical practice. Herein, we describe an unusual case of intramuscular HNST of the thigh. CASE REPORT: The patient was a 41-year-old man with no history of trauma who presented with a 3-month history of a palpable mass in the right thigh. Physical examination revealed a 4-cm, elastic hard, mobile, nontender mass. Magnetic resonance imaging exhibited a well-circumscribed intramuscular mass with low-to-intermediate signal intensity on T1-weighted sequences and higher signal intensity peripherally and lower signal intensity centrally, representing a target sign, on T2-weighted sequences. Complete surgical excision of the tumor was carried out. Microscopically, the tumor showed dual histological components of both schwannoma and neurofibroma. Immunohistochemically, the schwannomatous component was strongly and diffusely positive for S-100 protein and negative for CD34, while the neurofibromatous component contained CD34-positive fibroblasts and S-100 protein-positive Schwann cells. Epithelial membrane antigen was negative for both components. These findings were consistent with a diagnosis of HNST (hybrid schwannoma/neurofibroma). The patient had no evidence of local recurrence and no neurological deficit at the final follow-up. CONCLUSION: Although extremely rare, HNST should be included in the extended differential diagnosis of a well-circumscribed, intramuscular soft-tissue mass in the extremities, particularly in young and early middle-aged adults.