DIAGNOSIS: OLFACTORY NEUROCYTOMA.
The current WHO classification lists only one tumor assumed to originate from olfactory receptor cells: the olfactory neuroblastoma, a malignant tumor which tends to infiltrate adjacent structures and even the cerebral frontal lobes (4). It may spread metastatically to local lymph nodes and over the blood stream. It is characterized histologically by cellular sheets and nests of round cells with scant fibrillar cytoplasm and round dark nuclei. Neurogenic differentiation includes rosettes of the Homer-Wright type and expression of synaptophysin. Olfactory neuroblastomas are typically located high in the nasal cavity. However, the tumors are seen as far afield as ethmoid sinuses since the developing olfactory placode of early embryogenesis covers a large portion of the nasal mucosa. After birth, the neuroepithelium is replaced by respiratory mucosa but persistence of neural elements may occur (4).
A malignant neurogenic tumor of the nasal cavity was first described by Berger and colleagues in 1924 in a 50-year-old male patient (2). The neurogenic nature of the tumor was established on account of rosettes and neurofibrillary fascicles. The malignant nature of the tumor was indicated by a high mitotic ratio, a high nuclear-cytoplasmic ratio and necrosis. The authors termed the neoplasia "olfactory esthesioneuroepithelioma" ("esthésioneuroépitheliome olfactif"). Their tumor fits well into the entity of olfactory neuroblastoma of the current WHO classification (4).
In 1926, Berger and Coutard reported a case, which they considered to be the benign counterpart of the malignant olfactory tumor reported two years earlier and which they called "olfactory esthesioneurocytoma" ("esthésioneurocytome olfactif") (1). The patient, a 52-year-old female, suffered several relapses after a 13-year tumor-free interval. The tumor cells were characterized by their ability to form abundant neurofibrils. Cellular areas intermingled with fibrillar areas. Rosettes were absent. The tumor showed only rare mitoses. The olfactory neurocytoma reported by Berger and Coutard (1) closely resembles the tumor described in the present report.
Very few cases of olfactory neurocytoma have been reported after the original description. McCormack and Harris described 3 adult patients ranging in age between 29 and 58 years (9). Lindström and Lindström contributed the case of a 44-year-old male patient (7). Some case reports assigned the term "olfactory neurocytoma" to malignant tumors (8).
The histologic features of olfactory neurocytoma bear resemblance to the central neurocytoma (3). However, the central neurocytoma is assumed to take origin from central neurons or neuronal precursor cells on account of its intracerebral localization. A unique case of a central neurocytoma arising within a mature cystic teratoma of the ovary abutted onto an ependyma-lined cyst within the teratoma and, hence, recapitulated the typical location of neurocytoma adjacent to the lateral ventricle (6). The cells of origin of an exceptional case of neurocytoma arising in the pelvis remain to be identified (5). By contrast, olfactory neurocytoma is a neurogenic tumor which is supposed to take origin from olfactory receptor cells (1). The tumor is sufficiently distinguished from central neurocytoma and from olfactory neuroblastoma to fulfill the criteria of a clinicopathological entity in its own right.
Contributed by Antje Bornemann, MD, and Assen Koitschev, MD