Fibromatosis: a potential sequela of neuromuscular choristoma

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Neuromuscular choristoma (NMC) is a rare peripheral nerve lesion in which mature skeletal muscle fibers lie within the nerve and its fascicles. Given limited follow-up, its natural history is poorly understood. The occurrence of aggressive fibromatosis in one of the authors' patients and its occurrence in reported cases suggests an etiological relationship between the 2 lesions. This study attempts to explain the association and its frequency.


All cases of NMCs seen in consultation or treated at the Mayo Clinic were identified. Demographic and clinical data were reviewed in cases with coexistent aggressive fibromatosis. Pathology and neuroimaging studies were reexamined. In addition, an extensive literature review was performed to explore the association of NMC with aggressive fibromatosis, with special attention given to pathological and imaging characteristics and the development of aggressive fibromatosis.


The authors identified 10 patients with a diagnosis of NMC who were treated at the Mayo Clinic between 1992 and 2010. Four of 5 with adequate follow-up had developed a definite or suspected aggressive fibromatosis. A review of the initial pathological specimens in these cases revealed no evidence of fibromatosis, but all of the lesions exhibited accompanying hypocellular collagenous tissue. On MR images, all cases showed areas of low signal intensity, which significantly differed from muscle, nerve, and NMC components. On available serial MR imaging studies, aggressive fibromatosis seemed to originate in such lower-intensity regions. In the 18 previously reported cases of NMC, 5 patients developed recurrent masses diagnosed as either definite (2 cases) or possible (3 cases) fibromatosis. Review of the published imaging studies in these cases suggests the presence of lower intensity areas similar to those observed in the 10 patients treated at the Mayo Clinic.


This study confirms that the development of aggressive fibromatosis in patients with NMC has been underreported. A direct relationship between the NMC and the development of aggressive fibromatosis is suggested by pathological and neuroimaging evidence.

Abbreviation used in this paper: NMC = neuromuscular choristoma.

Article Information

Address correspondence to: Robert J. Spinner, M.D., Mayo Clinic, 200 First Street SW, Gonda 8-214S, Rochester, Minnesota 55905. email:

Please include this information when citing this paper: published online August 5, 2011; DOI: 10.3171/2011.6.JNS102171.

© AANS, except where prohibited by US copyright law.



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    Case 1. A: Intraoperative photograph showing the gross appearance of the sciatic nerve (arrow) at the time of the initial biopsy. The nerve appears diffusely enlarged without evidence of a discrete tumor. B: Specimen obtained at initial biopsy: complete cross-section of 2 nerve fascicles containing abundant pink skeletal muscle fibers (asterisks) admixed with nerve fibers (dotted area). H & E, original magnification × 400. C: Specimen obtained at initial biopsy: cross-section of nerve fascicle demonstrating intrafascicular skeletal muscle fibers after immunostaining for muscle marker. Desmin, original magnification × 200. D: Intraoperative photograph showing the gross appearance of the aggressive fibromatosis (arrowhead) adjacent to the sciatic nerve (arrow) 8 years after the initial biopsy. Note how one hamstring motor branch (thick curved arrow in upper part of image) seems to be closely involved with the tumor. E and F: Sections of lesion resected 8 years after the initial biopsy showing fibromatosis. The fibromatosis was seen to be associated with residual NMC (F). H & E, original magnification × 400.

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    Case 1. Magnetic resonance images obtained preoperatively (A–C), 8 years after the first surgery (open biopsy) (D–F), and 8 months after second surgery (resection of the fibromatosis) (G–I). A: Axial STIR image obtained at the midthigh demonstrating a low signal intensity mass (arrows) in the posterior compartment with focal areas of very low signal intensity (arrowheads) representing fibrous tissue. B: Axial STIR image at the level of the ischial tuberosity and greater trochanter showing the low signal intensity, oval mass (arrows) with mild signal heterogeneity but no areas of high T2 signal. C: Sagittal T1-weighted image of the thigh without contrast showing the mass longitudinally with a sheetlike area (posteriorly) of very low signal intensity (arrows) representing fibrous tissue. D: Axial T2-weighted upper thigh MR image with fat suppression showing an interval increase in the size of the mass, which now has areas of high T2 signal intensity (arrows) and intermediate signal intensity consistent with fluid and muscle-like soft tissue as well as areas of very low signal intensity (arrowheads) representing the fibrous portion of the tumor. E: Axial T2-weighted image with fat suppression at the same level as B showing intermediate signal intensity muscle-like tissue (arrows) with very low signal intensity tissue around and through the mass (arrowheads) consistent with fibrous tissue. F: Sagittal Gd-enhanced T1-weighted image with fat suppression showing the areas of enhancement (asterisk) as well as the very low signal intensity tissue (arrows) extending longitudinally within the thigh. G: Axial T2-weighted image with fat suppression in the upper thigh showing a small amount of heterogeneous tissue remaining. Note persistent very low signal intensity fibrous tissue (arrowheads). H: Axial T2-weighted image with fat suppression at the same level as B and E showing no change in the primarily fibrous tissue with associated intratumoral muscle at this level. I: Sagittal Gd-enhanced T1-weighted image with fat suppression showing persistence of the upper fibrous portion of the mass (arrows) with decrease in size in the enhancing portion of the tumor inferiorly (thick curved arrow) on the second postoperative imaging study (G–I), as compared with F (the initial postoperative study). No Gd-enhanced preoperative studies were available for review.

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    Case 2. Magnetic resonance images obtained preoperatively (A–C) and 5 years after CT-guided biopsy (D–F). A: Axial T2-weighted image with fat suppression at the level of the acetabulum shows a mass (arrow) with heterogeneous but overall low signal. An area of lower signal consistent with fibromatosis (arrowhead) is seen at the periphery of the mass encasing the sciatic nerve. B: Axial T1-weighted image at the same level shows the mass with low signal extending into the sciatic notch. Note atrophy in the gluteus maximus muscle (plus signs). C: Axial Gd-enhanced T1-weighted image with fat suppression shows enhancement of the mass (arrows) with some focal, nonenhancing low signal areas. The enhancement within the gluteus maximus muscle is related to subacute denervation change. D: Axial T1-weighted image at the level of the ischial tuberosity shows enlargement the heterogeneously low signal mass, which is now causing very significant mass effect on the adjacent gluteus maximus muscle (plus signs). E: Axial T1-weighted image obtained slightly superior to D showing the increase in size of the mass as well as further intrapelvic extension. Again noted are sheetlike areas of low signal representing fibrous tissue (arrowheads). Total hip arthroplasty causes artifact on this image. F: Coronal T1-weighted image shows the full extent of the mass through the sciatic notch as well as the prominent muscular atrophy.

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    Case 4. Coronal T1-weighted image of the right brachial plexus shows an isointense mass infiltrating and encasing the brachial plexus (asterisk). The nerves of the plexus proximal to the mass are enlarged (arrows). Note low signal, sheetlike areas around and through the mass (arrowheads).

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    Case 3. A: Intraoperative photograph at the time of the initial sciatic nerve fascicular biopsy in the mid-thigh region. B: Development of a thigh mass 4 months postoperatively in the region of the previous biopsy. C: Axial MR imaging image of the thigh showing a large, heterogeneous mass (arrows) associated with the sciatic nerve with several sheetlike low-density areas consistent with fibrous tissue (arrowhead). D: Gross-resected specimen of the posterior compartment of the thigh, including the sciatic nerve. Coronal section shows the fibrous mass with areas consistent with muscular tissue.



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