A resected case of schwannomatosis involving an extremely rare phrenic neurogenic plexiform schwannoma

Central MessageTwo phrenic neurogenesis plexiform schwannoma were successfully treated by ingenuity for surgery. A surgical approach that can be combined with palpation to ensure that no lesion remains is useful. Two phrenic neurogenesis plexiform schwannoma were successfully treated by ingenuity for surgery. A surgical approach that can be combined with palpation to ensure that no lesion remains is useful. In the thoracic cavity, neurogenic tumors are most commonly found in the posterior mediastinum, and most are solitary. Schwannoma is the most common neurogenic tumor and has multiple variants. The plexiform type is the rarest variant, with high potential for recurrence, unlike other variants. Plexiform schwannomas rarely occur in deep soft tissues or internal organs.1Berg J.C. Scheithauer B.W. Spinner R.J. Allen C.M. Koutlas I.G. Plexiform schwannoma: a clinicopathologic overview with emphasis on the head and neck region.Hum Pathol. 2008; 39: 633-640Crossref PubMed Scopus (89) Google Scholar We report a case of resection of schwannomatosis including plexiform schwannoma of phrenic nerve development; to our knowledge, no similar case has been reported thus far. The institutional review board of Seirei Mikatahara General Hospital approved the publication of the data (approval number: 22-57, approval date: January 10, 2023). The patient provided informed written consent for the publication of the study data. The patient was a 47-year-old woman with a history of surgery for left phrenic neurogenic solitary schwannoma localized on the left side of the heart 20 years previously who suffered from left phrenic nerve palsy. Computed tomography incidentally revealed multinodular lesions extending from her left neck to the anterior mediastinum (region A) and on the left side of the heart (region B). In addition, a 12-mm solitary nodule in contact with the left first rib (region C) was observed (Figure 1). Thoracoscopic resection of region C was performed to establish a definitive diagnosis to determine the treatment strategy. A diagnosis of benign schwannoma was made, and complete resection of the residual lesion was planned at a later date. We performed surgery with a small thoracotomy with the assistance of a thoracoscope for region B (Video 1) and a transmanubrial approach that not only a simple cervical incision but also a left anterior thoracotomy along the upper edge of the second rib was added to cut the manubrium for region A (Video 2). The 2 regions were continuous via a normal phrenic nerve. Many of the very small nodules were located a small distance from the nerve and difficult to see with the naked eye, so palpation was useful to identify any minimal remaining nodules. It was possible to remove all lesions as a group by dissecting the phrenic nerve at a normal site near its root. Microscopically, the resected tumors had regions predominantly consisting of the Antoni A region with a palisade arrangement of cell nuclei and formation of Verocay bodies. The Antoni B region was occasionally observed, but mitosis was rarely seen (Figure 2). These findings confirmed 2 plexiform schwannomas of the left phrenic neurogenesis (region A and B) and a solitary schwannoma of the left first intercostal neurogenesis (region C), leading to the diagnosis of schwannomatosis. After surgery, the patient recovered well and was discharged from our hospital on postoperative day 8. At the time of writing, only a few months have passed since the operation; however, her condition is good without signs of recurrence, new lesions, or complications. Plexiform schwannoma is the rarest variant, accounting for only 5% of all schwannomas. It has a high local recurrence rate (up to 50%), but it does not appear to have malignant or metastatic potential.1Berg J.C. Scheithauer B.W. Spinner R.J. Allen C.M. Koutlas I.G. Plexiform schwannoma: a clinicopathologic overview with emphasis on the head and neck region.Hum Pathol. 2008; 39: 633-640Crossref PubMed Scopus (89) Google Scholar Pathologically, it shows the same characteristics as conventional schwannomas. In the pathology literature, “plexiform” is often synonymous with “macroscopically multinodular lesion.”2Meis-Kindblom J.M. Enzinger F.M. Plexiform malignant peripheral nerve sheath tumor of infancy and childhood.Am J Surg Pathol. 1994; 18: 479-485Crossref PubMed Scopus (46) Google Scholar There are also minute nodules that are only visible microscopically.1Berg J.C. Scheithauer B.W. Spinner R.J. Allen C.M. Koutlas I.G. Plexiform schwannoma: a clinicopathologic overview with emphasis on the head and neck region.Hum Pathol. 2008; 39: 633-640Crossref PubMed Scopus (89) Google Scholar Schwannoma is usually solitary, but multiple schwannomas can occur in the same or multiple nerves, called schwannomatosis. It is recognized in only approximately 10% of multiple nerve tumors, with an annual incidence of 0.58 cases per 1,000,000.3Antinheimo J. Sankila R. Carpén O. Pukkala E. Sainio M. Jääskeläinen J. Population-based analysis of sporadic and type 2 neurofibromatosis-associated meningiomas and schwannomas.Neurology. 2000; 54: 71-76Crossref PubMed Google Scholar Although approximately 5% of plexiform schwannomas are associated with schwannomatosis or type 2 neurofibromatosis,1Berg J.C. Scheithauer B.W. Spinner R.J. Allen C.M. Koutlas I.G. Plexiform schwannoma: a clinicopathologic overview with emphasis on the head and neck region.Hum Pathol. 2008; 39: 633-640Crossref PubMed Scopus (89) Google Scholar there are no reported cases of schwannomatosis involving phrenic schwannoma. Thus, our case is extremely rare. Complete resection of both the tumor and adjacent nerve fibers is recommended for plexiform schwannoma because of its high recurrence rate.4Ijichi K. Muto M. Masaki A. Murakami S. Recurrent plexiform schwannoma involving the carotid canal.Auris Nasus Larynx. 2018; 45: 358-361Abstract Full Text Full Text PDF PubMed Scopus (5) Google Scholar Nerve paralysis is unavoidable because of transection of the involuntary nerve, so a wait-and-see approach should be considered if there are no symptoms and the size is stable. However, if resection is performed, en bloc resection should still be considered to avoid multiple surgeries for recurrence. In this case, the lesions could be completely resected together because phrenic nerve palsy had already occurred before surgery, and it was clearly progressive. Plexiform schwannoma has many very fine nodules, so palpation is useful for accurately determining whether there are any residual lesions. This case is considered to be highly suggestive. Although extremely rare, it is highly suggestive that plexiform schwannoma may also appear in the thoracic cavity. In addition, by our presenting rare preoperative imaging findings, readers can assume this disease exists. It is also suggestive that palpation is very useful and important during surgery. This case demonstrates that new lesions can continue to form from nerves throughout the body. It is not clear how long follow-up should be continued; however, careful follow-up is required in the future.