PMC6892774_01
MRI of sacrococcygeal mass prior to initial resection. (A) Axial view of fat-saturated T2-weighted and (B) contrast-enhanced T1-weighted sequences demonstrate a lobulated expansile mass confined to the soft tissues affixed between the gluteal muscles. The mass on sagittal view is (C) T2 hyperintense well-encapsulated within the post-sacral soft tissues without invasion into the sacrococcygeal space and (D) heterogeneously enhancing with central necrosis.
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F1
Pelvic imaging of the asymptomatic mass prior to initial resection revealed an expansile, non-eroding mass in the post-sacral soft tissues (Figure 1).
Histopathology of primary postsacral mass and lung metastasis. (A) Left: photomicrographs of initially resected postsacral mass demonstrates tumor composed of papillary structures lined by cuboidal glial cells with an intermediate layer of myxoid stroma (original magnification, x100). Middle: numerous mucin-rich microcysts (short arrows) and mitotic figures (thin arrows) (original magnification x200). Right: tumor cells are diffusely positive for GFAP (original magnification, x100). (B) Initial lung biopsy of the right lower lobe nodule (8 mm) demonstrates a metastatic mucin-rich tumor (left photo) with adjacent non-neoplastic lung and (right) metastatic focus demonstrating diffuse reactivity with GFAP (original magnification x100).
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F2
The 12.1 cm perisacral soft tissue mass displayed tumor composed of papillary structures with central hyalinized blood cells surrounded by cuboidal to elongated tumor cells with an intermediate layer of myxoid stroma (Figure 2A, left). Focally, few mitotic figures were identified (Figure 2A, middle). The tumor cells showed diffuse and strong immunoreactivity for glial fibrillary acidic protein (GFAP) (Figure 2A, right) and patchy immunoreactivity for pan-cytokeratin and epithelial membrane antigen (EMA) (not shown). The biopsied lung nodule that had enlarged over a 2-year interval displayed similar morphological features to the perisacral tumor, showing large granular tumor cells populated in a fibromyxoid background and strong immunoreactivity for GFAP (Figure 2B), consistent with metastatic MPE (WHO grade I).
Pulmonary oligometastases upon detection of recurrent sacrococcygeal mass. (A) Axial views of the lungs revealing a small, discrete homogeneously hyperdense nodule (black circle) in the right lower lobe (left) that had doubled in size since initial resection (8 mm from 4 mm) and enlarging left lower lobe (middle) and right lower lobe (right) metastases. (B) Recurrent post-sacral mass on axial (left) and sagittal (middle, right) fat-saturated contrast-enhanced T1-weighted sequences is heterogeneously enhancing and multilobulated in appearance as it extends through the soft tissues without invasion into the coccyx.
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F3
Other left and right lower lobe nodules were both stable at 3 mm (Figure 3A). At the tip of the coccyx was a heterogeneously enhancing lobular mass, measuring 3.5 x 2.1 x 3.1 cm (Figure 3B).
Restaging of recurrent soft tissue mass prior to and following resection. (A) Pre-resection sagittal view with contrast-enhanced T1-weighted image showing a multilobulated mass extending from the first through fourth coccygeal segments bordered by a thin plane of fat interposed between the tumor and coccyx without evidence of coccygeal invasion (black arrow). (B) Status post-coccygectomy and resection cavity (black arrow) of the previously described associated lobulated mass.
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F4
A thin plane of fat was interposed between the tumor and coccyx without evidence of coccygeal invasion (Figure 4A). An MRI 5 weeks later showed a stable post-operative resection cavity (Figure 4B).