An unusual pelvic mass

Highlights

• •Differential diagnosis for a solid pelvic mass includes pelvic schwannoma, especially if the mass if fixed to the sidewall or sacrum.
• •Pelvic MRI is helpful for evaluation, followed by CT-guided biopsy to confirm the diagnosis.
• •Schwannomas are typically benign lesions and do not require surgical intervention or resection unless the patient is symptomatic.
• •We recommend a minimally invasive approach when resection is preferred. This is best accomplished with interdisciplinary expertise.

Abstract

Background

The differential diagnosis for a solid pelvic mass is broad and includes non-gynecologic masses such as retroperitoneal schwannoma. Theses benign nerve-sheath tumors can be mistaken for adnexal masses or cause non-specific bulk symptoms, which may lead patients to present to their Ob/Gyn or ultimately be referred to gynecologic oncologists for evaluation and possible resection.

Cases

We discuss two cases of pelvic schwannoma: a 79-year-old woman who initially presented with a two-year history of left lower extremity cramping, paresthesia, and back pain, and a 40-year-old woman with right-sided flank pain and worsening dysmenorrhea, who presented with initial concern for adnexal mass.

Conclusion

The differential diagnosis for a smooth, fixed, pre-sacral or sidewall mass on pelvic exam includes pelvic schwannoma. These nerve sheath tumors are typically benign; however, can cause a variety of symptoms due to regional mass effect and may significantly impact quality of life. Associated symptoms, if present, may be non-specific or difficult to localize (i.e. pelvic pain/fullness, urinary symptoms, constipation, and radiculopathy), which can lead to a delay in diagnosis if a comprehensive pelvic exam is not performed or if suspicion for an etiology of non-gynecologic origin is not considered. Recommended workup includes pelvic MRI followed by CT-guided biopsy. Management is guided by the patient’s symptoms; if surgery is warranted, a minimally invasive, interdisciplinary approach is strongly preferred.

1. Introduction

Gynecologists are well-aware of gynecologic causes of pelvic masses and adept at screening for these issues, but routine exams can also present an opportunity to recognize non-gynecologic masses. The differential for solid ovarian masses typically includes sex cord stromal tumors, germ cell tumors, metastatic tumors, and fibromas, but certain clues on exam (in our case a smooth, fixed, pre-sacral lesion) may suggest non-gynecologic etiology. Schwannomas are tumors arising from the myelin sheath of peripheral nerves, most commonly in the head and neck or upper extremities (Godet et al., xxxx, Debaibi et al., 2022). Rarely, schwannomas can present in the retroperitoneal space (Godet et al., xxxx, Debaibi et al., 2022). Most cases (>90 %) are benign but can present with myriad non-specific symptoms due to compression of local structures, which can make these tumors difficult to diagnose (Godet et al., xxxx, Debaibi et al., 2022, Wong et al., 2010). Retroperitoneal schwannomas have been described in case reports, but little has been discussed in the literature in terms of specific recommendations for imaging, referral pathways, and surgical approach, especially as it relates to masses identified in the pelvis (Godet et al., xxxx, Debaibi et al., 2022, Wong et al., 2010, Cury et al., 2007, Asmz Rahman and Sharmin, 2015). Here we present two cases of retroperitoneal pelvic masses – found to be pelvic schwannomas – to highlight exam features suspicious for this type of lesion, describe associated symptoms, and discuss options for management. We aim to highlight recommendations for minimally invasive approaches for patients interested in surgery given the benign nature of these tumors, as well as the most appropriate referral pathway for this issue which likely requires interdisciplinary care.

2. Cases

2.1. Case 1

A 79-year-old woman initially presented with a two-year history of left lower extremity cramping and paresthesia which caused insomnia and need for movement every few hours. She denied any bowel, bladder, or pelvic symptoms. Her past surgical history was notable for prior total abdominal hysterectomy. She presented to an outside facility ED for severe back pain, at which time CT abdomen-pelvis and subsequent pelvic MRI demonstrated a large left-sided pelvic mass with emanation from the S1 foramen, abutting the piriformis muscle and internal iliac vessels (Fig. 1, Fig. 2). CT-guided biopsy confirmed schwannoma with epithelioid features. She was referred to surgical oncology and recommended for observation versus combination surgery with orthopedic oncology. After a period of observation, she was referred to neurosurgery for resection given her worsening and bothersome symptoms, at which time gynecologic oncology also became involved to assist with the surgical approach.

Fig. 1.

T1 pre-operative MRI, sagittal view, demonstrating a pre-sacral pelvic mass.

Fig. 2.

T1 pre-operative MRI, axial view, demonstrating a pre-sacral pelvic mass.

Her exam revealed a smooth, 5–6 cm fixed mass along the left pelvic sidewall and sacral border which was immobile and non-tender on exam with no nodularity. Neurological exam was without deficits. She underwent robotic-assisted excision of a left nerve-sheath tumor. The pararectal and para-vesical spaces were opened, and the tumor was visible between external iliac vein and internal iliac artery extending deep into retroperitoneum. The nerve sheet was incised identifying the tumor with its capsule. The capsule was cleared of the nerve tumor and the mass was dissected away from the nerve fibers and surrounding structures. The specimen was removed via a mini laparotomy incision in an endocatch bag. The patient experienced significant improvement in her symptoms post-operatively.

2.2. Case 2

A 40-year-old woman was initially referred to gynecologic oncology for evaluation of a right-sided complex adnexal mass noted on pelvic ultrasound. Ovarian tumor markers were within normal limits. At that time, she reported right buttock/lower extremity pain and numbness with prolonged sitting and exercise (most noticeable after long bike rides), right flank pain, right lower quadrant pain with increased abdominal pressure, and increasing pelvic pain and bleeding with menses. She was incidentally found to have a large, smooth, fixed pre-sacral pelvic mass on bimanual exam. Subsequent CT abdomen/pelvis revealed a complex pelvic mass which appeared contiguous with the right S1 nerve root (rather than the right ovary), which was confirmed by MRI. She was referred to neurosurgery and underwent robotic resection via a transperitoneal approach. At the time of her post-operative MRI (3 months following the procedure), the patient reported that her low back pain, abdominal discomfort, and radiculopathy had significantly improved, and she was back to her usual activities without limitation.

3. Discussion

Despite differing presentations, these cases both describe a smooth, fixed, pre-sacral or sidewall lesion found to be a pelvic schwannoma. These nerve sheath tumors are typically benign, however can cause a variety of symptoms due to regional mass effect and may significantly impact quality of life. Associated symptoms, if present, may be non-specific or difficult to localize (i.e. pelvic pain/fullness, urinary symptoms, constipation, and radiculopathy), which can lead to a delay in diagnosis if a comprehensive pelvic exam is not performed or if suspicion for an etiology of non-gynecologic or origin is not considered. Furthermore, concurrent, more common disease states may be present to which symptoms may be erroneously attributed (i.e. endometriosis or ovarian masses, as in one of the cases discussed). General Ob/Gyn physicians should be familiar with this diagnosis to be able to identify abnormalities on bimanual exam and facilitate referral to the appropriate surgeons, as well as prevent other unnecessary testing or workup. A schwannoma can easily be mistaken for a solid adnexal mass on pelvic ultrasound. However, adnexal masses typically have at least some mobility, while schwannomas are smooth, firm and fixed to the sidewall.

From the experiences at our institution, we recommend initial characterization with pelvic MRI to delineate if the mass is a nerve sheath tumor, followed by CT-guided biopsy to confirm the diagnosis. If there is concern for vascular invasion, a CT angiogram prior to surgery can be considered to provide additional information. In terms of post-operative follow up imaging, repeat MRI at 3 months allows for interval remodeling of the nerve and evaluation of associated postsurgical changes. If there are any concerns based on patient symptoms, imaging can be performed earlier.

There are a few key notions to highlight regarding surgical management. First, the referral pathway for pelvic schwannoma may vary by institution but will likely benefit from interdisciplinary care. At our institution, surgery is done by gynecologic oncology and neurosurgery, which we have found to be an effective collaboration of expertise and skills, namely, familiarity with the retroperitoneal spaces and nerve root stimulation for identification. Although there is extensive vascularity in the retroperitoneum, once within the nerve sheath and outside the tumor capsule, vasculature is limited to tumor vasculature and should not involve the deep pelvic vessels. Given that these tumors are benign, and surgery is to enhance quality of life, it is especially important to minimize surgical intervention and associated morbidity where able. A conservative approach (i.e. observation with follow up imaging) should be preferred in asymptomatic patients, or in patients who are poor surgical candidates. If surgery is recommended to alleviate symptoms, a minimally invasive approach (i.e. using robotic-assisted laparoscopic surgery) should be preferred. Total resection of the tumor should only be attempted if anatomy and location of the tumor permits; otherwise, patients may benefit from debulking alone to improve their symptoms.

4. Consent

Written informed consent was obtained from the patients described above for publication of this case report and accompanying images. Patients who did not provide consent were omitted. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.

CRediT authorship contribution statement

Marie-Véronique Poirier: Writing – review & editing, Writing – original draft, Visualization, Resources, Conceptualization. Vikram B. Chakravarthy: Writing – review & editing, Supervision, Conceptualization. Floor Backes: Writing – review & editing, Supervision, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.