Surgical Approach for a Gluteal Neurofibroma

Abstract

Background

Localized neurofibromas typically demonstrate a benign course and are often followed unless the patient opts for removal due to cosmetic concerns or symptoms caused by their size. The workup of neurofibromas largely consists of some form of biopsy to confirm the diagnosis. Once confirmed through histology, the tumor can be surgically removed or followed until the patient decides on removal. The surgical removal of these tumors can be quite complex due to their infiltration into nearby structures.

Summary

A 74-year-old male developed a progressively enlarging right gluteal mass following a fall from standing several months prior to presentation. Over the following months, the mass caused pelvic impingement, necessitating surgical intervention. Notably, this case emphasizes the importance of interdisciplinary collaboration. Preoperative imaging, reviewed by a team of urology, orthopedic oncology, and colorectal surgery specialists, facilitated the formation of a skilled surgical team and guided the optimal surgical approach for resection of the neurofibroma.

Conclusion

The surgical approach to resection can be complicated by the locally advanced nature of neurofibromas. Interdisciplinary review of high-quality preoperative imaging is vital for surgical planning. This case exemplifies the importance of interdisciplinary evaluation. High-quality MRI findings, revealing pelvic tissue distortion and a "levator ani cap," informed the decision for a multi-surgeon team and a minimally invasive perineal approach.

Key Words

mass; surgery

Case Description

A 74-year-old man presented with a growing, painful buttock mass initially thought to be a post-fall hematoma. After referral to general surgery, an ultrasound raised suspicion for a mass, and biopsy confirmed a spindle cell proliferation suggestive of a peripheral nerve sheath tumor. Subsequent orthopedic consultation and pelvic MRI revealed a large (12 × 10 × 16 cm), T2 heterogeneous bright mass centered within the right buttock and extending into the right ischioanal fossa. Imaging showed the mass exerted a leftward mass effect upon the rectum and base of the prostate, which was closely adjacent to the right inferior pubic symphysis and right corpus cavernosum. An interdisciplinary surgical team (orthopedics, colorectal, and urology) planned for mass resection. The patient was counseled about the potential outcomes, including positive margins and/or the need for abdominoperineal resection and colostomy, prostatectomy, or penectomy.

Discussion

As the most prevalent peripheral nerve sheath tumor (PNST),¹ neurofibromas arise from the endoneurium and surrounding connective tissues, causing mass effect on adjacent structures.¹ In this case, the patient presented with a sporadic localized tumor with minimal risk of malignant transformation.

Neurofibromas can appear as either:

• Asymptomatic cosmetic bumps on the neck, chest, back, and limbs.
• Symptomatic, growing, and palpable masses.^1,2

Confirming a diagnosis typically requires a core needle biopsy or surgical excision.³ Histology shows scattered spindled cells with poorly defined borders within a collagenous matrix containing mast cells.^1,4 The nuclei of these tumors are often described as small, hyperchromatic, and wavy, with few mitoses present.¹ Immunohistochemical evaluation demonstrating CD 34, myelin basic protein, and S100 (positive in 50% of tumors) can further aid in the diagnosis of neurofibromas.^1,5

Localized neurofibromas have an excellent prognosis. While many cases require only clinical monitoring, surgical removal becomes the preferred course of action when patients experience:

• Unwanted cosmetic changes due to the tumor's presence.
• Symptoms like pain or discomfort caused by the mass effect of the tumor.
• Peripheral neurological issues ranging from nerve pain to gait abnormalities and weakness.⁴

Imaging identified a pelvic mass near the prostate and urethra (Figures 1 and 2), concerning for potential involvement of these critical structures. While imaging did not confirm direct invasion, the mass's close proximity mandated consultation with a subspecialist. Surgical intervention became necessary due to the patient's pain and the potential risk to nearby anatomy. The surgical team faced the challenge of achieving a complete resection (R0 resection) with minimal complications. This balancing act required careful planning to determine the optimal surgical approach that would effectively remove the mass while preserving nearby structures and minimizing functional impairment.

Figure 1. Axial Fat-suppressed T2-weighted MRI. Published with Permission

Figure 2. Sagittal Fat-suppressed T2-weighted MRI. Published with Permission

Preoperative planning involved a multidisciplinary approach to optimize the surgical strategy for this complex case. The tumor's proximity to vital structures raised the possibility of a combined transabdominal and transperineal approach. Discussions focused on the feasibility of minimally invasive or robotic techniques to facilitate transabdominal dissection. A thorough review of imaging with the radiologist played a critical role in determining the optimal approach, potentially including minimally invasive or robotic techniques for transabdominal dissection. This collaborative planning ensured a successful surgical strategy.

Imaging identified a crucial detail: a "levator ani cap" (indicated by the arrow in Figures 3 and 4). This finding, caused by the neurofibroma pushing down on the levator ani muscles, confirmed the mass was entirely extra-pelvic. Based on this key information obtained from imaging, the surgeons chose a minimally invasive perineal approach with the patient positioned prone.

Figure 3. Sagittal Nonfat-suppressed T1-weighted MRI. Published with Permission

Figure 4. Sagittal Nonfat-suppressed T1-weighted MRI. Published with Permission

The patient was positioned prone, and following standard prepping and drapping of the area around the perineum and bilateral, a curvilinear incision along the sacrum and coccyx provided access to the well-encapsulated mass. Using a combination of precise cutting and gentle separation, we carefully freed the mass all the way around. This technique ensured complete tumor removal while minimizing risk to surrounding critical structures, including the pudendal nerve, sciatic nerve complex, rectum, external sphincter complex, prostate, and crus of the penis. To further ensure a safe resection, a digital rectal exam and flexible sigmoidoscopy were performed intraoperatively, confirming no injury to the anorectal area. Additionally, a thorough examination assessed the prostate, urethra, and base of the penis for any potential iatrogenic injury. The surgery concluded successfully, achieving complete tumor removal with negative margins as confirmed by post-operative pathology. The patient recovered well and exhibited no signs of recurrence at the ten-month follow-up.

Conclusion

Preoperative planning, in this case, hinged on meticulous radiological evaluation. MRI identified a cap on the tumor superiorly, consistent with the levator ani complex. This crucial finding dictated a perineal approach, deviating from the initial consideration of peritoneal access. Additionally, tumor involvement near the rectum, pudendal nerve, and urethra necessitated preoperative consultations with colorectal and urologic specialists, optimizing surgical strategy and minimizing complications.

Lessons Learned

For optimal surgical outcomes in complex pelvic tumors, meticulous preoperative planning is essential. This involves assembling an interdisciplinary team of surgeons with complementary expertise. Careful review of high-quality imaging by the radiologist, specifically tailored to the surgical approach, is crucial for optimal oncological resection and patient outcomes.

Authors

Lemons W^a; Markovich B^b; Lindsay B^c; Murken D^d

Author Affiliations

1. West Virginia University School of Medicine, J.W. Ruby Memorial Hospital, Morgantown, WV 26506
2. Department of Radiology, West Virginia University School of Medicine, J.W. Ruby Memorial Hospital, Morgantown, WV 26506
3. Department of Orthopedic Surgery, West Virginia University School of Medicine, J.W. Ruby Memorial Hospital, Morgantown, WV 26506
4. Department of Surgery, West Virginia University School of Medicine, J.W. Ruby Memorial Hospital, Morgantown, WV 26506

Corresponding Author

Wesley Lemons, MD
VCU School of Medicine
1200 E. Broad Street
9th Floor
Box 980153
Richmond, VA 23298
Email: wesley.lemons@vcuhealth.org

Disclosure Statement

The authors have no conflicts of interest to disclose.

Funding/Support

The authors have no relevant financial relationships or in-kind support to disclose.

Received: September 30, 2021
Revision received: January 25, 2022
Accepted: January 26, 2022

References

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3. Graham DS, Russell TA, Eckardt MA, et al. Oncologic Accuracy of Image-guided Percutaneous Core-Needle Biopsy of Peripheral Nerve Sheath Tumors at a High-volume Sarcoma Center. Am J Clin Oncol. 2019;42(10):739-743. doi:10.1097/COC.0000000000000591
4. Safaee M, Parsa AT, Barbaro NM, et al. Association of tumor location, extent of resection, and neurofibromatosis status with clinical outcomes for 221 spinal nerve sheath tumors. Neurosurg Focus. 2015;39(2):E5. doi:10.3171/2015.5.FOCUS15183
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