PMC8168713_01
Preoperative: (a) sagittal T1-weighted image of the lower lumbar spine, sacrum, and coccyx reveals an extensive, well-circumscribed subcutaneous lesion (star) at the dorsal aspect of the pelvis, which returns homogenous low signal and infiltrates the middle osseous part of the coccyx. (b) Axial T2-weighted image with fat saturation at the level of the coccyx shows the communication of the subcutaneous multiseptated lesion (thick arrow), which returns high signal indicative of fluid and/or proteinaceous material with the destroyed infiltrated central part of the coccyx. (c) Sagittal CT reconstruction of the same ROI shows the different density between the fluid-filled main subcutaneous lesion and the higher, soft-tissue like density of the lesion that causes osteolysis of the coccyx (arrow).
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F1
T2-weighted images, similar to cerebrospinal fluid but there was no evidence of a connection between the lesion and the subarachnoid space [Figure 1a and b]. The computed tomography (CT) scan further documented focal erosion of the coccyx at the lesion site [Figure 1c].
Intraoperative image showing a multiloculated cyst with secretion of yellowish thick fluid (star) through its wall.
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F2
At surgery, the cyst was whitish-gray in color, multiloculated, adherent to the periosteum of the sacral bone and coccyx, and continuous with the fascia of the paravertebral muscles [Figure 2].
Postoperative: (a) postoperative sagittal CT reconstruction shows complete removal of the subcutaneous tissue (star) and surgical excision of the distal part of the coccyx. (b) The axial CT image shows minor changes at the level of the distal part of the coccyx without evidence of subcutaneous recurrent mass or collection (arrow).
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F3
The postoperative CT confirmed adequate lesion removal [Figure 3].
Necrobiotic areas containing amorphous eosinophilic material that is surrounded by inflammatory reaction with prominent macrophages, including multinucleated giant cells: (a) x40 and (b) x100.
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F4
In addition, there was amorphous necrotic material similar to fibrinoid necrosis surrounded by a histiocytic reaction with granulomatous features [Figure 4a and b].