Uncommon retroperitoneal mass in a young adult: A rare case report of retroperitoneal schwannoma and review of diagnostic challenges

Abstract

Introduction and importance

Retroperitoneal schwannomas are extremely rare, benign tumors originating from Schwann cells in peripheral nerve sheaths, with few reported cases. Their deep location and nonspecific symptoms make preoperative diagnosis challenging, often requiring imaging and surgical resection for confirmation. This case highlights an uncommon presentation of retroperitoneal schwannoma in a young patient, emphasizing its rarity.

Case presentation

An 18-year-old male presented with a progressively enlarging, non-tender mass in the left flank. Imaging revealed an 8 × 7 cm well-circumscribed, encapsulated mass displacing adjacent major vessels without invasion. The patient underwent successful surgical resection, and histopathology confirmed a benign schwannoma. Immunohistochemistry showed strong S100 protein positivity, with no signs of malignancy. Follow-up was uneventful, with no recurrence at six months.

Discussion

Retroperitoneal schwannomas, typically slow-growing and benign, are infrequently encountered. Due to their nonspecific presentation, they often reach considerable size before detection. Imaging may suggest diagnosis but is not definitive, making surgical excision essential for confirmation. Complete resection is generally recommended to reduce recurrence, though partial excision may be appropriate when adjacent critical structures are involved.

Conclusion

Retroperitoneal schwannomas are rare and challenging to diagnose preoperatively. Complete surgical resection remains the primary approach, allowing histological confirmation and reducing recurrence risk. This case underscores the importance of considering retroperitoneal schwannomas in young patients presenting with atypical retroperitoneal masses.

Highlights

• •Retroperitoneal schwannomas are rare, benign tumors that often grow silently and can reach significant sizes before being detected, making early diagnosis challenging. These tumors typically do not present with specific symptoms, leading to delayed identification.
• •Diagnosis can be difficult due to the nonspecific nature of symptoms and the imaging characteristics, which may overlap with other retroperitoneal conditions. MRI and CT are particularly useful for preoperative assessment, helping to identify the mass, its location, and relationship to adjacent structures.
• •Surgical resection remains the treatment of choice for retroperitoneal schwannomas, with complete excision being crucial to minimize the risk of recurrence and achieve optimal long-term outcomes.
• •This case report emphasizes the importance of including schwannomas in the differential diagnosis of retroperitoneal masses, particularly in young patients who may present with atypical or vague symptoms.
• •Early detection and complete surgical resection offer excellent prognosis.

1. Introduction

Schwannomas are tumors originating from Schwann cells in cranial and peripheral nerve sheaths, with retroperitoneal schwannomas representing a rare cause of retroperitoneal masses [1,2]. These tumors are typically benign, slow-growing, and encapsulated, though they carry some malignant potential, especially in association with neurofibromatosis type 1 (NF1) [3]. Diagnosing retroperitoneal schwannomas is challenging due to their nonspecific symptoms and deep location, often requiring imaging and surgical resection for confirmation [1,2]. Our aim is to describe a rare case of retroperitoneal schwannoma in an 18-year-old patient. This case report has been prepared in line with the SCARE criteria [4].

2. Case presentation

An 18-year-old male with no prior surgical or family history presented to the outpatient department with a progressively enlarging, non-tender mass in the left flank that had developed over the past year. The patient denied any associated symptoms such as abdominal pain, weight loss, fever, or changes in bowel habits.

On clinical examination, a firm, rounded mass approximately 8 cm in diameter was palpated in the left flank. There were no signs of skin changes or palpable lymphadenopathy. Routine blood tests, including complete blood count, liver function tests, and renal function tests, were unremarkable.

An initial ultrasound identified an 8 × 7 cm paravertebral, well-circumscribed, hypoechoic mass adjacent to the left psoas muscle. A contrast-enhanced CT scan confirmed an 8 × 7 cm heterogeneous, latero-vertebral mass displacing the adjacent aorta and inferior vena cava without signs of vascular or neural foramen invasion (Fig. 1). No calcifications or necrotic regions were seen. MRI provided further characterization, showing an encapsulated retroperitoneal mass with isointense signals on T1-weighted imaging and heterogeneous signals on T2-weighted imaging, including hyperintense and isointense areas, consistent with a benign nerve sheath tumor.

Fig. 1.

CT scan showed an 8 × 7 cm latero-vertebral mass (yellow arrow), well-circumscribed and heterogeneous, displacing the adjacent aorta (red arrow) and vein (blue arrow) without invasion. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Given these findings, surgical intervention was planned, and the patient underwent a laparotomy through a midline incision. Intraoperative exploration revealed a well-encapsulated, firm mass along the left psoas, displacing the aorta and vena cava without evidence of direct invasion into surrounding vascular structures (Fig. 2). Careful dissection allowed for total excision of the mass with minimal blood loss. The mass was successfully resected without complications.

Fig. 2.

A mass located anterior to the left psoas (yellow star), adjacent to the aorta (yellow arrow), displacing nearby structures without evidence of invasion.

Postoperatively, the patient had an uneventful recovery and was discharged on postoperative day 3. Histopathological examination confirmed a myxoid schwannoma with typical Antoni A and B areas and no features of malignancy. Immunohistochemistry showed strong, diffuse positivity for S100 protein, affirming the diagnosis. The patient was advised on periodic follow-up, and at the 6-month review, no signs of recurrence were observed, and the patient remained asymptomatic.

3. Discussion

Schwannomas typically present in the head, neck, or extremities, originating from cranial or peripheral nerves [5]. Retroperitoneal schwannomas, however, are rare, comprising only 0.7 % to 2.7 % of all schwannomas [6]. These tumors most commonly affect female patients aged 20 to 60 [5,7]. However, cases in younger patients have been reported, albeit infrequently. In a study of 82 patients with retroperitoneal schwannoma, the age range extended from 6 months to 70 years, indicating that these tumors can occur across a wide age spectrum [5]. While the occurrence of retroperitoneal schwannoma in an 18-year-old patient is unusual, it underscores the importance of considering this diagnosis even in younger individuals presenting with retroperitoneal masses [5,7]. Due to the spacious nature of the retroperitoneum, these tumors often grow to a significant size before diagnosis, with reported median diameters of up to 8.7 cm (ranging from 4 to 15 cm) [8,9].

There is only one previously reported case of retroperitoneal schwannoma in an adolescent, described by Moazam in 1982, involving a 14-year-old patient. The current case, involving an 18-year-old, adds to this limited number of pediatric occurrences [10]. Both cases highlight the rare occurrence of retroperitoneal schwannomas in younger individuals. The presentation in adolescents is unusual given the typical adult age range, emphasizing the need for clinicians to consider this diagnosis in young patients with retroperitoneal masses, despite its rarity [10,11].

Most retroperitoneal schwannomas are asymptomatic and are incidentally discovered during imaging for unrelated conditions [7]. When present, symptoms are nonspecific and may include abdominal discomfort, distension, back pain, a palpable mass, or urinary difficulties [12]. Neurological symptoms such as radiating pain or paralysis are rare [6,12].

Macroscopically, retroperitoneal schwannomas are usually solitary, well-circumscribed, and encapsulated [5,12]. Microscopically, they consist of Schwann cells with strong S100 protein positivity and alternating Antoni A (cell-rich, organized bundles) and Antoni B (cell-poor, myxoid) areas [5,12]. These tumors can exhibit secondary changes like cystic transformation, fibrosis, stromal edema, xanthomatous changes, perivascular hyalinization, and calcification, which may classify them as “ancient schwannomas” [11]. Malignant transformation is exceedingly rare, but when it occurs, malignant schwannomas behave like high-grade sarcomas with high rates of local recurrence and metastasis [5,11].

Preoperative diagnosis is challenging due to nonspecific imaging features [9,13]. Cystic areas with semisolid components are commonly seen on imaging [13]. Ultrasound and CT scans are valuable for evaluating retroperitoneal masses. CT scans often reveal well-circumscribed, heterogeneous masses with central low attenuation, peripheral enhancement, and possible cystic degeneration that displace rather than invade adjacent structures [13]. MRI can better assess the tumor's origin, vascular involvement, and relationship to surrounding organs. Schwannomas typically appear isointense on T1-weighted images and hyperintense on T2-weighted images [11,14].

The role of preoperative biopsy remains controversial [15]. While CT-guided biopsy or fine-needle aspiration (FNA) may aid diagnosis, some physicians avoid it due to potential complications like bleeding, infection, or tumor seeding, although others report successful diagnoses using these techniques [15,16].

Complete surgical excision is the gold standard for treatment [12,17]. There is debate over the necessity of extensive resections involving adjacent organs to achieve clear margins [12,17]. Some argue that enucleation or partial excision may be sufficient for benign tumors, especially those involving critical adjacent structures, with no observed increase in recurrence or malignant transformation in partially excised cases [[17], [18], [19]]. Proponents of complete resection emphasize the risk of malignancy, which cannot be definitively excluded preoperatively or intraoperatively, even with frozen section analysis, as well as the potential for recurrence [19].

The prognosis for retroperitoneal schwannomas is generally favorable, with recurrence rates of 5–10 % attributed to incomplete excision [20]. Follow-up imaging with CT or MRI is often recommended within 6–12 months postoperatively, though this practice is not systematic [12,21].

4. Conclusion

Retroperitoneal schwannomas are rare and present significant diagnostic challenges due to their nonspecific clinical and radiological features, often making preoperative identification difficult [5,11]. Typically, a definitive diagnosis is only achieved after complete surgical resection and histological examination of the tumor [17]. Surgical treatment can be complex, particularly with large schwannomas that involve nearby organs, sometimes requiring partial or complete resection of these adjacent structures to ensure optimal outcomes [3,17].

Patient consent

Written informed consent was obtained from the patient for the publication of this case report and its accompanying images. A copy of the written consent is available for the Editor-in-Chief of this journal to review upon request.

Ethical approval

Ethical approval is not applicable/waived at our institution.

Declaration of Generative AI and AI-assisted technologies in the writing process

AI tools were not used for the elaboration of the manuscript.

Funding sources

This research did not receive funding from any specific grant provided by public, commercial, or not-for-profit organizations.

Grant information

The author(s) declared that no grants were involved in supporting this work.

Declaration of competing interest

No conflicts of interest.