Retroperitoneal melanotic schwannoma: ultrasonographic features

A para-aortic malignant melanotic nerve sheath tumor mimicking a gastrointestinal stromal tumor: a rare case report and review of literature

Background

Malignant melanotic nerve sheath tumor (MMNST), formerly called melanotic schwannoma, is a rare tumor of neural crest derivation which most frequently arises from the region of spinal or autonomic nerves near the midline. Recent studies have reported malignant behavior of MMNST, and there still has no standard management guidelines. Intra-abdominal MMNST, which has never been reviewed as an entity, is even rarer. In this study, we present a rare case of a cystic MMNST arising from the para-aortic region and mimicking an intra-abdominal gastrointestinal stromal tumor (GIST), and review the literature regarding MMNSTs located in the abdominal cavity.

Case presentation

A 59-year-old female was incidentally found a tumor located in the left para-aortic area by non-contrast computed tomography. A Magnetic Resonance Imaging showed a cystic mass originated from the inferior mesenteric artery (IMA) territory. A GIST was initially diagnosed. The tumor was resected en bloc by laparoscopic surgery and was found between mesocolon and Gerota’s fascia with blood supply of IMA. Grossly, dark brown materials were noted at the inner surface of the cystic wall. Microscopically, the tumor cells were melanin-containing, and no psammomatous bodies were present. Immunohistochemically, the tumor showed positivity for MART1, HMB45, collagen IV, and SOX10, and negativity for AE1/AE3. MMNST was favored over malignant melanoma, since the tumor was located near ganglia and had cells with less atypical cytology and a low mitotic rate, and subsequent adjuvant radiotherapy was performed. The patient was alive with no evidence of recurrent or metastatic disease 11 months after radiotherapy.

Conclusions

Our review of abdominal MMNST cases showed a female predominance, with an average age of 54.8 years, and a trend toward being a larger tumor showing cystic or necrotic changes. Local recurrence and metastasis rate were reviewed, and both showed a low rate. Diagnosis of MMNST should combine all the available findings, and complete excision of the tumor should be performed, followed by long-term patient monitoring.

Novel response to neoadjuvant anti-PD1 therapy for a patient with retrocaval melanotic schwannoma

Melanotic schwannoma is a rare nerve sheath tumor composed of melanin-producing Schwann cells with the potential for metastasis. These tumors can be associated with familial tumor syndromes and can cause significant symptoms related to nerve compression and mass effect. Due to the rarity of these lesions, they can be initially misidentified as melanocytomas, pigmented dermatofibrosarcoma protuberans, neurofibromas or malignant melanomas. Surgical excision is the mainstay of treatment with limited benefit from adjuvant systemic chemotherapy or radiation. Modern treatments with immune checkpoint blockade have demonstrated significant improvements in progression-free and overall survival for a variety of cancer histologies; however, anti-PD1 therapy has yet to be evaluated in patients with melanotic schwannoma. This report demonstrates a significant improvement in symptomatology and tumor stability with neoadjuvant anti-PD1 therapy for a retrocaval melanotic schwannoma initially masquerading as malignant melanoma. This report demonstrates the potential benefit of a novel therapeutic option for patients with melanotic schwannoma.

Laparoscopic resection of a giant retroperitoneal melanotic schwannoma

Background

Retroperitoneal schwannomas are extremely rare, as they account for only 3% of retroperitoneal tumors. Clinical symptoms are nonspecific and of late onset, meaning that these tumors are diagnosed at an advanced stage. Surgical resection is required for histological diagnosis and to prevent possible malignant transformation. Celioscopy offers numerous benefits, reducing postoperative pain and speeding up the patient's return to autonomy, but it can pose a real challenge due to the size of these lesions.

Case presentation

We report a case of laparoscopic resection of a very large right-sided retroperitoneal schwannoma, with a particular histological form.

Conclusion

Surgical resection in a single unit remains the golden rule, and a laparoscopy can be proposed when the diagnosis is beyond doubt. The large size of the retroperitoneal melanotic schwannomas, a common feature, increases surgical difficulties but is not a contraindication to this approach.

A large pelvic mass in a 39-year-old man

Schwannomas are encapsulated, usually benign, tumors composed of well-differentiated Schwann cells, arising from the neural sheath of peripheral nerves. The most common type of benign schwannoma is the acoustic neuroma arising from the eighth cranial nerve. Retroperitoneal schwannomas account for 0.5-3% of the retroperitoneal tumors in most series. We present a case of a 39-year-old man with a pelvic mass, arising from a sacral nerve root, diagnosed as a schwannoma.

Analysis of 82 cases of retroperitoneal schwannoma

BACKGROUND

The aim of the study was to improve the diagnosis and treatment of retroperitoneal schwannoma by analysing clinical manifestations and postoperative course of this rare disease.

METHODS

A retrospective analysis of 82 patients with retroperitoneal schwannoma between January 1951 and September 2004 was carried out.

RESULTS

The patients were 38 (46%) men and 44 (54%) women between the ages of 6 months and 70 years. The interval between clinical manifestation and diagnosis ranged from 10 days to 2 years. The main symptoms were abdominal distension (30.5%) and abdominal pain (20.7%). Only in 13 patients (15.9%) a correct preoperative diagnosis was made by either ultrasound-guided biopsy, computed tomography scanning or magnetic resonance imaging. All patients received operative therapy. Sixty patients (73.2%) underwent a total resection; 13 patients (15.9%) subtotal resection, but 9 patients (11.0%) had only an examination and a biopsy. Two patients (2.4%) had multiple schwannomas and two others had a simultaneous malignancy (adenocarcinoma of the ascending colon and squamous-cell carcinoma of the lung, respectively). Most of the retroperitoneal schwannomas were close to the spine. Pathological results showed 81 (98.8%) were benign schwannoma and 1 (1.2%) was a malignant one. The tumour size ranged from 3 to 22 cm. One benign schwannoma recurred 3 years after the operation. The patient with malignant schwannoma died 18 months after the operation because of metastasized disease.

CONCLUSION

Most of the retroperitoneal schwannomas are benign. It is difficult to make an accurate preoperative diagnosis. However, with the preoperative assessment of ultrasound-guided fine-needle aspiration, computed tomography and magnetic resonance imaging, the accuracy of diagnosis could definitely be improved. Treatment depends solely on surgery. Malignant schwannomas are insensitive to chemotherapy and radiation, resulting in poor prognosis.