Neuromuscular Choristoma
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ANATOMIC PATHOLOGY Case Report Neuromuscular Choristoma ANDREW MITCHELL, MD,1 BERND W. SCHEITHAUER, MD,1 HELMUT OSTERTAG, MD,2 A. SEPEHRNIA, MD,3 AND AYDIN SAV, MD4 Downloaded from https://academic.oup.com/ajcp/article/103/4/460/1756042 by guest on 30 September 2021 Neuromuscular choristomas are rare, with only 13 cases having been ciated with choristoma. Despite its wide excision, a recurrence of the previously reported. They usually arise in association with large nerves, fibromatosis required a forequarter amputation. Theories of histogene and most often occur in the first decade of life. A few have been congen sis and the clinicopathologic features of the neuromuscular choristomas ital. Although resection is typically curative, in two instances partial reported to date are reviewed. The term "benign Triton tumor," al resection alone appears to have been followed by spontaneous regres though incorrectly applied to this lesion, should be reserved for benign, sion. The authors report an unusual example of an otherwise classic true nerve sheath neoplasms exhibiting myogenic differentiation. (Key neuromuscular choristoma where the lesion appeared to grow after in words: Choristoma; Hamartoma; Benign Triton tumor) Am J Clin Pa complete initial resection. Re-excision disclosed a fibromatosis unasso- thol 1995;103:460-465. The neuromuscular choristoma, a pseudotumor to which the skin. The right arm was normally developed, although minor limitation term "benign Triton tumor" has inappropriately been ap was noted in its range of motion. A computerized tomographic (CT) plied,'2 is a rare entity, usually occurring in the first decade of scan showed the lesion to be noninvasive, but compressive of adjacent life. To date, 13 cases have been reported.1"10 Arising in associ ribs. A sonogram demonstrated an inhomogeneous texture. No stig ation with a large nerve trunk, most form a grossly well-circum mata of neurofibromatosis were evident, and the family history was scribed mass. Histologically, they are characterized by a disor unremarkable. ganized admixture of mature skeletal muscle fibers and Surgical exploration of the right axilla and chest wall was undertaken, myelinated nerve. Resection has been curative in the majority revealing a tumor delicately adherent to and indenting the chest wall. of cases reported to date. We report a case, the second of its 5 Although it did not involve surrounding soft tissue, it was evident that type, wherein initial surgery was followed by an apparent re nerves of the brachial plexus entered and exited the mass. Within the currence that proved to be a supervening fibromatosis. lesion, entering nerves broke up into bundles. Varying in thickness and The histogenesis of neuromuscular choristoma remains a orientation, they were interspersed with muscle fibers and bellies in controversial issue. Proposed theories include muscle fiber en such a way as to suggest an organized neuromuscular unit. Stimulation trapment within developing nerve branches,3 hamartomous 1 of nerves proximal to the tumor resulted in contraction of the mass, overgrowth of muscle spindles, and mesenchymal metaplasia whereas stimulation of exiting nerves produced normal muscle con of neuroectoderm," which is a process known to occur in nor 12 traction within the distal extremity. In that gross total resection would mal embryogenesis. have required division of major nerves and their reanastamosis, only a partial resection was performed, one sparing as many brachial plexus CASE REPORT branches as possible. Microscopic examination disclosed a neuromus cular choristoma (Figs. 1-3). A 4-month-old white female infant underwent evaluation of a mass In the immediate postoperative period, paresis of the arm was evi involving the right axilla and chest wall, which was first noted by her dent, an EMG showing abnormalities of all three major nerves. Two mother. The lesion was of uncertain duration, but in retrospect was months thereafter, the right upper arm was mobile, but motor function thought to have been present since birth. The infant had been otherwise of the forearm and hand was still severely affected. At 5 months, healthy and did not seem discomforted by the mass. Physical examina strength in the extremity was approaching normal. During the interval, tion, at age 4 months, revealed a normally developed infant with a firm, however, an apparent recurrence was noted at the operative site. On discrete, vaguely lobulated 5 cm axillary mass that lay adjacent to the CT scan, a 4.5 cm irregularly demarcated mass was again seen to lie right chest wall. It had undergone no significant increase in size, and within the indentation of the right chest wall. On examination 3 was non-tender as well as mobile, particularly relative to the overlying months thereafter, upper arm mobility was near normal, but complete loss of median and ulnar nerve function was evident. A CT and a mag netic resonance imaging scan performed 6 months after initial surgery From the' Department of Laboratory Medicine and Pathology Mayo showed the homogeneous lesion to measure 8 cm in its greatest dimen Clinic. Rochester, Minnesota;2Instilute of Pathology, and* Department sion, and to extend superiority to the level of the clavicle, dorsally to of Neurosurgery, Klinikum Nordstadl, Hannover, Germany;4Depart the scapula and inferiorly to the 6th rib (Fig. 4). Re-exploration of the ment of Pathology. Marmara University, Istanbul, Turkey. right chest wall region was performed. A fibromatosis and a small trau matic neuroma, both unassociated with choristoma, were identified Manuscript received June 28, 1994; revision accepted September 9, and grossly totally resected (Figs. 5 and 6). The procedure involved 1994. removal of a portion of the pectoralis major, a segment of the brachial Address reprint requests to Dr. Scheithauer: Department of Pathol ogy, Mayo Clinic, 200 First Street SW, Rochester, MN 55905. artery, and sacrifice of dorsal and medial portions of the brachial 460 MITCHELL ET AL. 461 Neuromuscular Choristoma Downloaded from https://academic.oup.com/ajcp/article/103/4/460/1756042 by guest on 30 September 2021 FIG. 1. Neuromuscular choristoma (original resection specimen). The FIG. 3. Neuromuscular choristoma (original resection specimen). The nodular lesion was composed of two distinct cell populations, including intimate association of nerve and muscle was highlighted in Bielschow- disordered bundles of skeletal muscle fibers, and an intimate admixture ski silver impregnation for axons (X250). of nerve fibers (hematoxylin and eosin, X250). plexus. Despite this aggressive resection, the CT finding of a recurrence 17 months afterward necessitated a curative right forequarter amputa tion. PATHOLOGY Tissues from the original and first "recurrence" resections were available for review. Representative tissues were formalin- fixed, routinely processed, and paraffin-embedded. Histochem- ical stains applied included hematoxylin and eosin with and without saffronin, hematoxylin-van Gieson, Luxol fast blue- periodic acid-Schiff (LFB-PAS), and the Bielschowski silver 1415 050986 CR-H--E.F- SP -1 3 FIG. 4. Postoperative fibromatosis 6 months after resection of the neu romuscular choristoma. Coronal (upper) Tl-weighted magnetic reso nance image of the mid thorax and an axial Tl -weighted image through FIG. 2. Neuromuscular choristoma (original resection specimen). Some the thorax at the level of the axillae (lower) demonstrates a 4.5 X 4.0 X nerve fiber bundles appeared to contain individual skeletal muscle fi 3.5 cm mass in the right axilla involving the brachial plexus. There is bers (hematoxylin and eosin, X250). associated deformity of the lateral chest wall. Vol. 103-No. 4 462 ANATOMIC PATHOLOGY Case cally diverse. They include malformative lesions as well as be nign and malignant neoplasms. Of these, the "Triton tumor," a malignant peripheral nerve sheath tumor (MPNST) with rhabdomyoblastic differentiation, is the most common.1314 Al though benign nerve sheath tumors, such as neurofibroma with myogenic differentiation, are exceedingly rare,15 non-neoplas- tic, presumably malformative lesions composed of well-formed nerve and mature skeletal muscle are being reported with in creasing frequency.1"10 Variously termed neuromuscular chor istoma or hamartoma, much discussion has surrounded their nature and histogenesis. The term "Triton tumor," as applied to nerve sheath tumors Downloaded from https://academic.oup.com/ajcp/article/103/4/460/1756042 by guest on 30 September 2021 composed in part of striated muscle, is derived from the sala mander of that name, a creature capable of regenerating lost limbs through the inductive influence of either normal residual or implanted nerve.16 The designation "malignant Triton tu mor" refers to an MPNST composed in part of a malignant rhabdomyoblastic component. The degree to which myogen- esis is expressed varies considerably, even from field to field within a given tumor. Although such rhabdomyoblasts may be poorly differentiated, often being embryonal in appearance, in FIG. 5. The gross specimen from the second resection, showing a rather some cases they are relatively mature, forming elongate myo circumscribed, fibrous lesion with a whorled cut surface. cytes or myotubes the cells of which exhibit regimented cross- striations. The majority of malignant Triton tumors occur in 14 impregnation method for axons. Utilizing the peroxidase-anti- association with neurofibromatosis. The term "benign Triton tumor"