PMC5364902_01
(A) CT showing extension of the intradiploic lesion into the right parietal bone. The outer and inner tables are thin with partial bone defects. (B) Axial MRI. Left, axial T1-weighted imaging; middle, axial T2-weighted imaging; right, diffusion-weighted imaging. (C) Coronal thin-slice drive-T2-weighted imaging. (D) Time- spatial labeling inversion pulse examination.
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F1
Computed tomography (CT) of the head showed a low-density area at the parietal intradiploic lesion where the inner and the outer tables were extremely thin with defective parts (Fig. 1A ). Magnetic resonance imaging (MRI) showed the contents of the lesion as hypointense on T1-weighted imaging (T1WI), hyperintense on T2-weighted imaging (T2WI) similar to the CSF, and hypo- to isointense on diffusion-weighted imaging (DWI) (Fig. 1B-D).
Intraoperative photographs. (A) The outer table is thin with partial defects. (B) The inner table and arachnoid granule-like protrusion. (C-F) Photographs after eliminating the inner table around the protrusion (C), after removing the protrusion (D), after duraplasty with periosteum (E), and after cranioplasty with hydroxyapatite (F). Photomicrograph of surgical specimens. (G) The arachnoid tissue undercoats the skull in the outer table with cyst wall, (hematoxylin and eosin (HE) stain, x100). (H) In the protrusion, meningothelial cells formed more than 10 layers and the nuclei are highly dense, but cells show no abnormal structures HE stain, x200). (I-K) Immunohistochemistry of the protruding specimen (upper, EMA stain; middle, Ki-67 stain; lower, PR stain, x200).
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F2
After the skin incision, the thinning outer table of the parietal skull bone with defective parts was revealed (Fig. 2A-F).  Histopathological examination revealed that the cyst wall comprised meningothelial cells in a single layer leading to the diagnosis of arachnoid cyst (Fig. 2G-K).