Case 1030 - A 41-Year Old Woman with a Posterior Cranial Fossa Mass

Contributed by Bunsho Asayama MD1, Yoshinobu Seo MD1, Yoshimaru Ozaki MD, PhD1, Satoshi Tanikawa MD2, Takanori Hirose MD, PhD3, Shinya Tanaka MD, PhD2, Hirohiko Nakamura MD, PhD1
1Department of Neurosurgery, Nakamura Memorial Hospital, Sapporo, Hokkaido, Japan
    2Department of Cancer Pathology, Hokkaido University Faculty of Medicine, Sapporo, Hokkaido, Japan
    3Department of Pathology for Regional Communication, Kobe University Hospital, Kobe, Japan


A 41-year-old previously healthy Japanese female presented with a 2-month-history of left occipital headache and dizziness. She had instability in standing on her left foot. A contrast-enhanced T1-weighted MR scan showed a high signal, 4.6 3.2 3.5 cm extra-axial mass containing a cyst located in the left posterior cranial fossa (Fig. 1a). It attached to the dura mater along the occipital bone and the petrous bone, a part of which was extending into the sigmoid sinus. Catheter angiography illustrated a hypervascular tumor fed by the middle meningeal artery and the ascending pharyngeal artery. The sigmoid sinus was occluded by the tumor invasion.

The patient underwent preoperative embolization of the tumor in order to decrease blood loss. Tumor resection was performed via left lateral suboccipital approach. The tumor was whitish-yellow, elastic hard, rich in fibrous tissue, and was strongly adherent to the dura mater. The cystic part was surrounded by soft membrane and filled with clear fluid. Brain and the tumor were clearly bounded by the arachnoid membrane. Gross total resection including the dura mater and the sigmoid sinus invaded by the tumor was achieved. After surgical treatment, her symptom gradually improved. She was discharged from our hospital with no neurological deficits.


Histopathological examination revealed the tumor had biphasic features. H&E staining (Figs 1b, 1c) showed a proliferation of short spindle cells in a vague arrangement with branching vascular structures and many broad bands of collagenous tissue. There were no whorl formation or psammoma bodies. Necrosis and mitoses were not present. Mixed with the spindle cell tumor, glandular duct structures of various sizes were found. These tissues consisted of serous and mucous acini and diversely dilated ducts. There were no atypical cells in this structure. Immunohistochemically, the spindle cells were diffusely positive for CD34 (Fig. 1d), vimentin (Fig. 1e), and nuclear STAT6 expression (Fig. 1f); EMA and progesterone receptor were negative. On the other hand, the glandular duct structures were positive for EMA (Fig. 1g), AE1/AE3, CK7 (Fig. 1h); CD34 and STAT6 were negative. And smooth muscle actin stain illustrated myoepithelial cell layer surrounding the secretory acini (Fig. 1i). The Ki67 index was 7%. What is your diagnosis?


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