Retroperitoneal malignant peripheral nerve sheath tumor in a patient with neurofibromatosis type 1: a case report

Abstract

Malignant peripheral nerve sheath tumors (MPNSTs) are rare, aggressive sarcomas originating from peripheral nerves or nerve sheath cells. They are often associated with neurofibromatosis type 1 (NF1) and have a poor prognosis due to high rates of recurrence and metastasis. We report a case of a 30-year-old female presenting with a retroperitoneal MPNST accompanied by metastases to the right pelvic wall and left rectus femoris muscle. The patient exhibited numerous café au lait spots densely distributed across the head, neck, trunk, and extremities, consistent with clinical features of NF1. Due to the limitations of gynecological ultrasonography, the mass was initially considered to originate from the adnexal region. Surgical interventions included exploratory laparotomy, partial colectomy, partial rectal resection, retroperitoneal neoplasms resection, and colostomy; however, only palliative resection was possible due to the tumor’s extensive invasion and inability to achieve clear margins. Histopathological examination, supported by immunohistochemical findings, confirmed the diagnosis of MPNST. Given the palliative nature of surgery and the short postoperative follow-up, the clinical outcome remains uncertain. This case highlights the diagnostic challenges of retroperitoneal MPNST, particularly in patients with NF1, and underscores the importance of early recognition and multidisciplinary management when curative resection is not achievable.

Malignant peripheral nerve sheath tumor (MPNST) is a rare and aggressive soft tissue sarcoma, accounting for approximately 5–10% of all sarcomas, with an estimated incidence of 1 per 100,000 individuals [1]. Nearly 50% of cases occur in patients with neurofibromatosis type 1 (NF1), in whom the risk of malignant transformation from preexisting nerve sheath lesions is substantially increased [2]. Histologically, MPNSTs are characterized by high-grade spindle cell morphology and marked biological heterogeneity.

MPNSTs most commonly arise in the trunk and extremities, whereas retroperitoneal involvement is exceedingly uncommon [3, 4]. Tumors in this location often present with nonspecific symptoms and imaging findings that overlap with gynecologic or gastrointestinal malignancies, posing significant diagnostic challenges [5–7]. In young female patients, retroperitoneal masses adjacent to the adnexa may reasonably be considered of gynecologic origin, particularly when initial evaluation relies on gynecologic ultrasonography, which has limited ability to assess deep retroperitoneal structures.

We report a young woman with NF1 who developed a large retroperitoneal MPNST that was initially considered an adnexal mass. This case highlights the diagnostic pitfalls associated with uncommon tumor location, the critical role of histopathological confirmation, and the challenges of surgical and prognostic decision-making when complete resection is not achievable.

Case presentation

Patient information

The patient was a 30-year-old female presenting with recurrent low back pain and urinary urgency for over 20 days, accompanied by tenesmus after defecation. Her body mass index (BMI) was 26.67 kg/m². Menstrual history was regular, and she had a history of cesarean section in June 2022. No other significant past medical history was reported. The patient’s occupation was not disclosed. No known family history of NF1 or other cancers.

Clinical findings

The patient first presented to the outpatient clinic on March 20, 2025, with intermittent lower abdominal discomfort. Multiple café-au-lait spots were noted on physical examination, though no palpable abdominal masses were detected at that time. Hospital admission occurred six days later at the patient’s request due to work-related obligations. Upon admission, a thorough physical examination was performed, revealing no new external abnormalities.

Timeline of events

As shown in Table 1.

Table 1.

Timeline of events

Date	Event	Details
March 20, 2025	Initial outpatient visit	Pain and urinary symptoms; adnexal mass detected.
March 26, 2025	Hospital admission on March 26 occurred at the patient’s request due to work-related obligations	Labs, inflammatory markers, and tumor markers within normal limits.
March 28–30, 2025	Imaging studies	CT: pelvic mass (119 × 83 mm) with heterogeneous enhancement, multiple nodules; MRI: heterogeneous signal, abnormal enhancement; colonoscopy: mucosal erosion, biopsy chronic inflammation (Figs. 1, 2, 3, 4 and 5).
April 1, 2025	Surgical intervention	Exploratory laparotomy with palliative resection of retroperitoneal neoplasms, partial colectomy, partial rectal resection, colostomy (Fig. 6a and d).
April 2–13, 2025	Postoperative care	Supportive care, gradual diet progression, stoma management; discharged on postoperative day 12.
April 21, 2025	postoperative follow-up of 20 days	CT: no evident abnormalities. Patient declined adjuvant therapy due to financial constraints.
July 10, 2025	postoperative follow-up of 100 days	Resumption of normal daily activities.
August 24, 2025	postoperative follow-up of 145 days	CT: no significant change in residual lesions. Monthly outpatient follow-up continues for stoma care.

Diagnostic assessment

The initial outpatient B-ultrasound showed a normal right ovary, while the left adnexa contained a predominantly solid mixed mass measuring 105 × 95 mm with well-defined borders and irregular contours. Color Doppler flow imaging (CDFI) revealed blood flow signals with a resistive index (RI) of 0.79, and the mass was initially suspected to be malignant. Laboratory investigations, including routine blood tests, inflammatory markers, and tumor markers (CEA, CA199, CA125, AFP), were all within normal limits.

Magnetic resonance imaging (MRI) Examination: Pelvic multiparametric MRI was performed using a United Imaging uMR880 3.0T MR scanner. The scan coverage extended from the upper border of L5 to the inferior border of the pubic symphysis, fully encompassing the pelvis, including the genitourinary organs, bowel, vessels, and surrounding soft tissues.

Computed tomography (CT) Examination: Whole-abdomen contrast-enhanced CT was performed using a Philips Spectral CT7500 256-slice scanner, covering from the diaphragm to the inferior pubic symphysis, including the entire abdominal and pelvic cavities.

During the third to fifth day after admission, an abdominal contrast-enhanced CT scan revealed a soft tissue mass in the pelvic cavity measuring 119 × 83 mm, with heterogeneous enhancement postcontrast (Fig. 1). Multiple nodular soft tissue densities were observed in the pelvic cavity, the largest measuring approximately 34 mm in diameter, also exhibiting postcontrast enhancement (Fig. 2). CT suggested a pelvic mass of ovarian origin, potentially cystadenocarcinoma, and the multiple nodules in the pelvic cavity and low-density lesions in the left rectus femoris muscle were considered possible metastatic deposits. Subsequent pelvic contrast-enhanced MRI revealed a heterogeneous mass with abnormal signal intensity, measuring approximately 119 × 83 mm. The lesion showed hypointensity on T1-weighted images, slightly hyperintense on T2-weighted images, and hyperintense on diffusion-weighted imaging (DWI) with low apparent diffusion coefficient (ADC) values, with heterogeneous enhancement after contrast administration (Fig. 3). Additionally, multiple oval-shaped abnormal signal foci were observed in the pelvic region and left rectus femoris muscle. These lesions were hypointense on T1-weighted images, hyperintense on T2-weighted images, and demonstrated postcontrast enhancement. The largest lesion measured approximately 27 × 41 mm (Figs. 4 and 5). Endoscopic colonoscopy reached the ileocecal area, revealing the appendix fossa, and showed swollen and eroded mucosa approximately 15 cm from the anus, for which a biopsy was performed. The remaining colonic and rectal mucosa appeared smooth. Pathology analysis of the biopsy revealed chronic inflammation of the mucosa with interstitial fibrous tissue hyperplasia. This result was non-diagnostic for the mass, likely reflecting adjacent compressed mucosa rather than the lesion itself, and could not confirm malignancy. These imaging and biopsy findings prompted reconsideration of the initial diagnosis of an ovarian malignancy. The retroperitoneal and mesenteric location, heterogeneous enhancement, and multiple nodular lesions raised suspicion for a retroperitoneal soft tissue sarcoma, ultimately guiding surgical intervention and further histopathological assessment.

Fig. 1.

Contrast-enhanced CT showing a large pelvic mass with heterogeneous enhancement. Axial contrast-enhanced CT scan (arterial phase) showing a large heterogeneous pelvic mass (arrow) occupying the central pelvic cavity. The lesion was initially considered as arising from the left adnexa due to its location. Heterogeneous enhancement and well-demarcated borders suggest a solid neoplasm rather than a cystic adnexal lesion

Fig. 2.

Multiple enhancing nodular soft tissue lesions in the pelvic cavity. Axial contrast-enhanced CT scan demonstrating multiple nodular soft tissue densities (arrows) within the pelvic cavity. These lesions exhibit mild to moderate enhancement and were initially considered possible metastatic deposits. Their distribution raised suspicion for multifocal involvement rather than a single gynecological tumor

Fig. 3.

Contrast-enhanced pelvic MRI showing a heterogeneous mass in the pelvic cavity. Axial T1-weighted contrast-enhanced MRI of the pelvis showing a large heterogeneous mass (arrow) with irregular borders in the central pelvic region. Heterogeneous post-contrast enhancement and ill-defined margins suggest aggressive behavior consistent with a soft tissue sarcoma

Fig. 4.

Heterogeneously enhancing pelvic mass on contrast-enhanced MRI. Axial T1-weighted contrast-enhanced MRI revealing a lobulated pelvic mass (arrow) with heterogeneous post-contrast enhancement compressing adjacent pelvic structures. Imaging features, including irregular contour and heterogeneity, supported suspicion for malignant peripheral nerve sheath tumor, differentiating it from typical ovarian neoplasms

Fig. 5.

Lesion within the left rectus femoris muscle on contrast-enhanced pelvic MRI. Axial T1-weighted contrast-enhanced MRI showing a nodular lesion (arrow) in the left rectus femoris muscle with heterogeneous enhancement. This lesion was suspicious for metastatic spread, highlighting the atypical metastatic pattern of retroperitoneal MPNST

Histopathology: Fresh surgical specimens, including retroperitoneal neoplasms and adjacent intestinal segments, were fixed in 10% neutral buffered formalin, processed routinely, embedded in paraffin, and sectioned at 4 μm. Sections were stained with hematoxylin and eosin for microscopic examination.

Postoperative pathological examination revealed a spindle cell tumor with areas of necrosis, measuring 13 × 9 × 6 cm, involving the retroperitoneum and part of the intestinal tube. Microscopy demonstrated densely packed spindle-shaped cells arranged in fascicles, with moderate to marked nuclear pleomorphism, frequent mitoses (approximately 12 per 10 high-power fields), and patchy necrosis. Focal areas of non-plexiform neurofibroma were identified, showing transition into higher-grade spindle cell proliferation, consistent with malignant transformation within an NF1-associated neurofibroma. The surgical margins at both ends of the intestine and the circumferential resection margin were negative for tumor involvement. As shown in Fig. 6a-c.

Fig. 6.

Histopathological features of the retroperitoneal neoplasms. a Densely packed spindle cells with pleomorphic nuclei, consistent with malignant peripheral nerve sheath tumor (MPNST). Hematoxylin and Eosin stain (×20; scale bar: 100 μm). b Spindle cells with wavy arrangement and mild nuclear atypia, consistent with atypical neurofibroma (ANF). Hematoxylin and Eosin stain (×7.5; scale bar: 400 μm). c Transition area between ANF and MPNST, showing progression from moderate atypia to pronounced nuclear atypia and increased cellularity. Hematoxylin and Eosin stain (×7.5; scale bar: 400 μm). d Immunohistochemistry for H3K27me3 (×10; scale bar: 200 μm) demonstrating loss of nuclear staining in tumor cells, supporting the diagnosis of MPNST

Immunohistochemistry: Immunohistochemical staining was performed on formalin-fixed, paraffin-embedded tissue sections using standard, validated protocols. Appropriate positive and negative controls were included for each marker to ensure staining reliability.

Immunohistochemical staining showed S-100 (focally positive), Vimentin (positive), and Ki-67 (~ 40% proliferation index). The complete loss of H3K27me3 expression (Fig. 6d) supports the diagnosis of MPNST. Other markers, including CD34, SOX-10, CD117, Dog-1, Desmin, CK (pan), NSE, STAT-6, NF, and SMA, were negative.

Combining clinical manifestations, imaging features and histopathological examination, the patient was diagnosed with NF1-associated MPNST with transition from neurofibroma [8, 9].

Therapeutic intervention

April 1, 2025, multidisciplinary consultations involving anorectal surgery, gynecology, urology, and orthopedics recommended exploratory laparotomy. During the operation, a large tumor was found in retroperitoneum and the mesentery of rectosigmoid junction (Fig. 7a), with a size of about 13 × 9 × 6 cm, demonstrating intact mesentery; The right pelvic wall touched a mass, about 3 × 4 cm in size, with relatively defined borders; The rectum and sigmoid colon were obviously compressed and displaced, and no obvious abnormalities observed in the bilateral ovaries and omentum (Fig. 7b). Given the extensive involvement of adjacent structures, complete primary resection was deemed technically infeasible without significant risk of morbidity. Based on these findings and the NCCN Soft Tissue Sarcoma Guidelines (Version 2.2022) [10], the surgical team decided to perform palliative resection of the retroperitoneal neoplasms to relieve gastrointestinal compression, with staged removal of the right pelvic wall lesion and consideration of adjuvant therapy according to postoperative pathology.

Fig. 7.

Intraoperative and gross pathological findings of the retroperitoneal neoplasms. a Intraoperative view showing a large retroperitoneal neoplasms embedded within the mesentery at the rectosigmoid junction. Tumor compresses surrounding bowel but does not infiltrate the ovaries. b Both ovaries appear grossly normal with no visible tumor involvement, confirming the mass is retroperitoneal in origin rather than gynecological. c Resected specimen including segments of colon, rectum, mesentery, and retroperitoneal mass, demonstrating the extent of tumor involvement and surgical margins. d Gross appearance of the incised specimen showing a multilobulated heterogeneous mass with areas of hemorrhage and necrosis, features characteristic of high-grade MPNST

A median abdominal incision of approximately 20 cm was made from the umbilicus to the symphysis pubis, and careful entry into the abdominal cavity was achieved. The descending and sigmoid colon were mobilized, and adhesions were dissected. The medial approach was used to isolate and divide the mesenteric artery and vein, providing optimal vascular control and safe mobilization of the tumor-bearing segments, which was particularly important given the tumor’s extensive retroperitoneal and mesenteric involvement. The retroperitoneal and intramesenteric tumors, along with portions of the descending colon, sigmoid colon, rectum, and mesentery, were resected en bloc (Fig. 7c) and sent for intraoperative frozen section analysis (Fig. 7d). Hemostasis was confirmed, and bilateral pelvic drainage tubes were placed and routed through the lower abdominal incisions.

Postoperatively, the patient received comprehensive supportive care, including anti-inflammatory therapy, fluid infusion, parenteral nutrition, and albumin supplementation. A liquid diet was initiated on postoperative day 2 and advanced to a semiliquid diet on postoperative day 3. Gastrointestinal function gradually returned, with stoma passage of gas noted on postoperative day 4 and bowel movements beginning on postoperative day 10. Follow-up abdominal CT on postoperative day 7 showed no evidence of obstruction. The drainage tubes were removed, and the patient was discharged without complications on postoperative day 12.

Follow-up and outcomes

At postoperative day 20, CT imaging revealed no evident abnormalities. Since postoperative day 40, the patient has attended monthly outpatient follow-up visits for stoma evaluation, with no abnormalities observed. By postoperative day 96, she had resumed normal daily activities. At postoperative day 100, a telephone follow-up confirmed good recovery without significant symptoms or clinical signs. A follow-up CT scan performed on postoperative day 145 demonstrated that residual lesions of uncertain nature, possibly metastatic, showed no interval growth. Given the limited follow-up period, long-term outcomes remain uncertain, and definitive conclusions cannot yet be drawn. The residual lesions remain unconfirmed, and a biopsy is planned during stoma reversal surgery to clarify their nature. Ongoing follow-up will further evaluate potential recurrence or progression.

Patient perspective

The patient expressed satisfaction with her surgical care and postoperative support. She understood the limitations of the procedure and declined further adjuvant therapy due to financial constraints, reflecting patient-centered decision-making.

Discussion

MPNST is a rare and highly heterogeneous sarcoma that poses substantial diagnostic and therapeutic challenges due to its morphological and immunophenotypic variability. In the present young woman case, the tumor’s anatomical proximity to the adnexa led to an initial consideration of a gynecologic origin. However, definitive diagnosis ultimately depended on histopathological evaluation, which demonstrated malignant spindle-cell proliferation arising in the background of a neurofibroma, consistent with NF1-associated MPNST.

Comparative literature highlights the diagnostic challenges of NF1-associated retroperitoneal tumors and underscores the necessity of histopathological confirmation. Yotsuya et al. [5] reported a patient with NF1 who developed a retroperitoneal mass pathologically confirmed as MPNST arising within a neurofibroma. Although imaging helped localize the lesion, the surrounding neurofibromas and heterogeneous tumor features prevented definitive diagnosis based solely on radiological findings, demonstrating that imaging alone may be insufficient and that histopathology is essential for accurate diagnosis. Saito et al. [11] described an NF1 patient who initially presented with symptoms of cholelithiasis and choledocholithiasis; during evaluation, a retroperitoneal mass was incidentally noted. Imaging and PET/CT could not definitively characterize the lesion, and biopsy ultimately confirmed it as a benign NF1-associated neurofibroma. Together, these cases, when compared to the present patient, emphasize that NF1-associated retroperitoneal masses—particularly MPNST—pose significant diagnostic challenges. Reliance on clinical symptoms and imaging alone may lead to uncertainty, and early histopathological assessment is critical for accurate diagnosis and timely management.

Surgical resection remains the cornerstone of MPNST management. Several studies have demonstrated that positive surgical margins or incomplete resections are associated with worse overall survival and higher local recurrence rates [12–14]. Complete resection with negative margins offers the best outcomes but is often infeasible for retroperitoneal tumors due to involvement of vital structures. Moreover, in patients with NF1-associated MPNST, where multiple neurofibromas and diffuse infiltration are common, radical surgery may result in substantial complication with limited survival benefit [15]. In the present case, the tumor extensively involved the retroperitoneum, mesentery, and adjacent bowel, making complete resection technically infeasible without unacceptable functional compromise. Importantly, the patient presented with significant compressive symptoms affecting bowel and urinary function but maintained good general condition and functional reserve. After multidisciplinary evaluation, palliative resection was therefore selected with the specific aim of symptom relief, improve bowel function, and preserve quality of life. Studies have demonstrated that palliative surgery in advanced soft tissue sarcoma, including MPNST, can substantially alleviate pain, improve mobility, and enhance short-term quality of life, even though it may not significantly prolong survival [16, 17]. Thus, when curative surgery is not feasible, carefully planned palliative resection may provide meaningful benefit to selected patients.

Adjuvant radiotherapy and chemotherapy are important components of multimodal treatment for MPNST, contributing to local control and systemic disease management. In the present case, although adjuvant therapy was recommended following multidisciplinary discussion, the patient declined further treatment primarily due to financial constraints. This decision had a direct impact on the overall treatment strategy and underscores the real-world influence of financial toxicity on cancer care. For this young patient with NF1 and advanced disease, the economic burden of prolonged oncologic therapy outweighed the perceived benefit, leading to prioritization of symptom relief and postoperative recovery over additional treatment. This case illustrates how socioeconomic factors can critically shape clinical decision-making, treatment adherence, and ultimately patient outcomes. Incorporating early financial counseling, social work support, and access to patient-assistance programs into multidisciplinary care may help patients facing similar circumstances better navigate treatment options and reduce disparities in access to comprehensive oncologic therapy.

NF1-associated MPNSTs generally carry a poorer prognosis than sporadic cases, with higher rates of recurrence and metastasis. In this patient, potential factors affecting prognosis included the large tumor size, the presence of residual lesions after palliative resection, and the lack of adjuvant therapy. At a short-term postoperative follow-up of 145 days, imaging revealed no radiologic progression of residual lesions suspicious for metastasis; however, this limited follow-up duration restricts prognostic interpretation, and continued monitoring is essential. The residual lesions suspicious for metastasis have not yet been pathologically confirmed. Fine-needle aspiration or biopsy is planned during future stoma reversal surgery to clarify their nature and better characterize disease status.

Strengths and Limitations: This case illustrates the challenges of diagnosing and managing retroperitoneal MPNST in the context of NF1, including rare metastatic patterns and complex surgical decision-making. Limitations include the short follow-up, the palliative nature of the surgery with incomplete resection, lack of adjuvant therapy limiting outcome generalizability, and the absence of molecular genetic testing. Moreover, these residual lesions currently lack pathological confirmation. Despite these limitations, the major educational value of this case lies in three aspects: First, it enhances understanding of NF1-associated MPNST diagnosis, especially for rare retroperitoneal presentations that can mimic gynecologic or gastrointestinal tumors. Second, it demonstrates the clinical significance of palliative resection in relieving symptoms and improving quality of life when radical surgery is not feasible. Third, it highlights the impact of socioeconomic factors on treatment decisions, emphasizing the need to consider patients’ financial circumstances in individualized cancer management.

Conclusion

This case provides an instructive example of NF1-associated retroperitoneal MPNST presenting as an adnexal mass, highlighting the potential for diagnostic ambiguity when pelvic tumors are evaluated primarily by gynecologic imaging. It reinforces the indispensable role of histopathology and immunohistochemistry in establishing the correct diagnosis in atypical retroperitoneal lesions. Moreover, the case illustrates the clinical rationale and potential symptomatic benefit of palliative resection when curative surgery is not feasible, as well as the impact of socioeconomic factors on treatment planning. Collectively, these findings underscore the need for diagnostic vigilance, multidisciplinary collaboration, and individualized, patient-centered decision-making in the management of complex sarcomas associated with NF1.

Abbreviations

MPNST

Malignant Peripheral Nerve Sheath Tumor

NF1

Neurofibromatosis Type 1

BMI

body mass index

RI

Resistive Index

CT

Computed Tomography

MRI

Magnetic Resonance Imaging

CDFI

Color Doppler Flow Imaging

DWI

Diffusion-Weighted Imaging

ADC

Apparent Diffusion Coefficient

Authors’ contributions

Luchuang Qian: Contributed to the conception of the case report, clinical management of the patient, and writing and drafting of the manuscript as the corresponding author.Xiaoming Ye: Participated in the surgical intervention and clinical management of the patient.Jing Sun: Participated in the surgical intervention and clinical management of the patient.All authors reviewed and approved the manuscript for publication.

Funding

Not applicable.

Data availability

All data supporting the findings of this case report are included within the manuscript. Additional information is available from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

Ethical approval for this case report was obtained from the Ethics Committee of Ningbo Yinzhou No. 2 Hospital. Written informed consent for participation in the study, including the use of clinical information, imaging findings, and pathological data, was obtained from the patient.

Consent for publication

Written informed consent was obtained from the patient for publication of this case report and any accompanying images. The patient confirmed understanding that all identifying information would be removed to ensure confidentiality.

Competing interests

The authors declare no competing interests.