Giant Pelvic Schwannoma in the Setting of Renal Cell Carcinoma

Introduction

• Schwannomas are benign peripheral nerve sheath tumors composed of Schwann cells that typically occur in the head, neck, and extremities.¹ They are thought to be caused by a mutation in the NF2 gene that leads to improper functioning of the merlin suppressor protein.²
• Pelvic schwannomas are very rare accounting for about 1-3% of all schwannomas.³ Once greater than 4.5cm, these tumors are classified as giant schwannomas.⁴
• Peak incidence occurs between age 20-50 with males and females equally affected.³
• They are difficult to diagnose as patients are asymptomatic until the tumor is large enough to compress surrounding structures leading to nonspecific symptoms.^4-7
• Official diagnosis can only be made after histopathological analysis. Pre-operative biopsy is an option but poses the risk of seeding if the tumor is malignant.¹
• Surgical resection of these tumors is the treatment of choice.^1,3-7
• Hypothesized that mutations in NF2 gene and SMARCB1 gene link the formation of schwannoma in neurofibromatosis type II with papillary renal cell carcinoma (RCC) and collecting duct RCC.^2,8,9

Case Description 

History:

• 46 y/o male presented to the general surgery team with back/pelvic pain, hematuria, and pelvic mass of unknown origin for surgical consult.
• Denied fever/chills, night sweats, unexpected weight change, numbness/tingling of lower extremities, flank pain, constipation, or urinary symptoms.
• PMH: RCC, hypertension, hypothyroidism, diabetes mellitus type II, gastroesophageal reflux disease, and benign prostatic hyperplasia, attentiondeficit hyperactivity disorder.
• RCC being monitored by urology and oncology through active surveillance.
• Medications: atenolol, lisinopril, metformin, levothyroxine, omeprazole, tamsulosin, tadalafil, alprazolam, amphetamine/dextroamphetamine.
• Allergies: Morphine.
• Past surgical history: None.
• Unremarkable social and family history.

Physical Exam:

Vitals:

• 156/82 mmHg, 95 bpm, 20 breaths/minute, 98.8F, 97% on room air.

Pre-operative:

• All systems unremarkable.

Post-operative: 

• No acute distress, resting comfortably in the room.
• Breath sounds clear and equal bilaterally in all auscultatory fields.
• Regular rate and rhythm, S1&S2 appreciated with no murmurs, DP and PT pulses 2+ bilaterally.
• Abdomen soft, non-distended, appropriately tender to palpation over midline incision site.
• Incision clean, dry, and intact with minimal serosanguineous staining on the dressing.
• A&O x4, lower extremity strength, motor function, and sensation all intact and equal bilaterally.

Pre-Operative Differential Dx: 

• Liposarcoma, fibrosarcoma, ganglioneuroma, Tarlov cyst, and pelvic schwannoma.

Labs/Diagnostics:

• Figure 3 shows pre-operative CT of abdomen/pelvis with IV contrast which revealed 11 x 8.6 x 9.5cm pelvic mass and 2.7 millimeter enhancing right renal lesion.
• CBC and CMP within normal limits aside from white count to 18,400 mm3 POD #1, which resolved by POD #2.
• Immunochemical stains performed by pathology included S100, SOX-10, Melan-A, and HMB-45.
• Figures 2 and 4 (not shown) show specimen in pathology with final findings of spindle cell neoplasm consistent with schwannoma.

Procedures:

• Cystoscopy with ureteral stent placement was performed first to provide better visualization of the ureters intra-operatively.
• Open exploratory laparotomy revealed a large, well-encapsulated pelvic mass tightly adhered to S1, S2, and sacrum.
• R2 resection of pelvic mass was then performed to preserve the sacral plexus and patient’s neurological function.

Outcome

• Post-operative course was uncomplicated aside from hematuria, abdominal pain, and leukocytosis on POD #1, all of which resolved by POD #2.
• Patient was discharged on POD #3 after pain control was achieved, Jackson-Pratt drain was removed, and patient was tolerating regular diet with adequate bowel function.
• Patient was notified once the official pathology report was released, and follow-up was scheduled to monitor for recurrence.

Discussion

• Complete surgical resection of pelvic schwannoma is the most effective treatment option with good prognosis postoperatively and low risk of recurrence.^1,3-7
• Controversy exists surrounding whether preservation of neurologic function versus complete resection of the tumor is more important in cases where the tumor is adhered to the sacral nerve plexus.^3,7
• Performing an R2 resection without knowing the histopathology of this tumor put our patient at higher risk of a poor outcome had this been a malignant tumor. This is a management problem that all providers face in pelvic masses of unknown origin.^1,3-6

Conclusion

• While there is not a well-studied genetic link between pelvic schwannoma and RCC, the case reports available show a strong potential for relationship between the two tumors.
• Pelvic schwannomas are difficult to diagnose and should be considered in the differential diagnosis of a patient with RCC exhibiting non-specific symptoms including low back pain, hematuria, or other urinary symptoms.