Schwannoma‐like tumor in the anterior cranial fossa immunonegative for Leu7 but immunopositive for Schwann/2E

Abstract

Schwannoma arising from the olfactory system, often called olfactory groove schwannoma (OGS), is rare, as the olfactory bulb and tract, belonging to the central nervous system, should lack Schwann cells. Another rare entity called olfactory ensheathing cell tumor (OECT) has been reported, which mimics clinical and radiological characteristics of OGS. Here, we report two rare cases of schwannoma-like tumor in the anterior cranial fossa that showed negative staining for Leu7, but positive staining for Schwann/2E, and discuss their origin. Two cases of mass lesions in the anterior cranial fossa in a 26-year-old man and a 24-year-old woman were successfully removed. Morphological examination of these tumors was compatible with a diagnosis of schwannoma. Immunohistochemically, both cases were negative for Leu7, yielding a diagnosis of OECT, but were positive for the schwannoma-specific marker, Schwann/2E. Immunohistochemical staining results in our two cases question the current assumption that OGS and OECT can be distinguished only by Leu7 staining pattern. In conclusion, the origins of OGS and OECT remain to be determined, and further studies in larger numbers of cases are needed to characterize these rare tumors in the anterior cranial fossa.

Utility of Schwann/2E and Sox10 in distinguishing CD57‐negative olfactory groove schwannoma from olfactory ensheathing cell tumor: A case report and review of the literature

“…[14][15][16] OECs are glial cells that form the axons of olfactory receptor neurons 17 and are located at the olfactory bulb base and in the axons extending from the ganglia of the olfactory bulb to the olfactory receptor cells. 2 Pathologically, OECs are considered to exhibit the properties of both astrocytes and Schwann cells. 18 In a review of OEC tumors, the average age was 34.7 (range 20-49) years, and a male-to-female ratio was 4/6.…”

“…Albeit a sensitive marker for Schwann cells, CD57 (Leu7) by itself cannot discriminate OGSs from OEC tumors, given that some OGSs are negative for CD57. [2][3][4] We herein report a patient who was diagnosed as having OGS based on positivity for Schwann/2E and Sox10 although the tumor was negative for CD57. We also provide a review of the literature on anterior skull base tumors.…”

Olfactory Groove Schwannoma—A Case Report and Literature Review

“…6 Still, there is a theory suggesting the origin of Schwann cells from multipotent mesenchymal cells after an injury. 2 Non-developmental hypotheses believe that intracranial schwannomas are extra-axial lesions arising from adjacent structures that present Schwann cells, namely, the meningeal branches of the trigeminal, the anterior ethmoidal nerves and the nerve plexus of dural vessels that innervate the anterior cranial fossa. 8,9 Yasuda et al raised the question about the origin of Schwann cells in some olfactory groove tumors, and attributed it to the olfactory ensheathing cells (OECs), suggesting, in this way, another entity: olfactory ensheathing cell tumor (OECT).…”

“…1,3 Extremely rare and with an enigmatic origin, schwannomas are found in the anterior cranial fossa, specially in the olfactory groove. 2 We report the case of an olfactory groove schwannoma (OGS) along with a brief literature review of the pathogenesis and origin of the schwanommas.…”

Why are olfactory ensheathing cell tumors so rare?

“…Lack of Leu7 expression, however, does not necessarily mean that the tumor is definitely an OEC tumor, as ~ 20% of schwannomas are negative for Leu7 [89]. Recently, two cases of schwannoma-like tumors in the anterior cranial fossa were described to be immunonegative for Leu7 but immunopositive for Schwann/2E, a marker for myelinating Schwann cells [90] and some schwannoma tumors [91]. Leu7 is expressed by Schwann cells in early development and then lost; when Schwann cells myelinate axons their expression of Leu7 is again up-regulated (reviewed in [78]).…”