DISCUSSION
The route of spread of various types of
malignancy may be hematogeneous, lymphatic, or neurotrophic through
the perineural space. The neoplastic neural invasion was first
reported by Cruveithier in 1942. Ballantyne et al in 1963 determined
that neural invasion was relatively commonplace in carcinomas of the
head and neck and frequently influenced the outcome of the treated
cases. Neural invasion may be an exclusive form of tumor progression
or may be one of several manifestations of cancer's annihilating
ability. The perineural space is a tissue plane of less resistance
when tumors have access to it. The dissemination of the tumor along
the perineural pathway assures both a centrifugal and centripetal
direction. The propensity of squamous cell carcinoma and salivary
gland carcinomas of the head and neck disseminate preferentially in
the perineural pattern and are often associated with more aggressive
tumor behavior. (Ballantyne et al, 1963). Occasionally, basal cell
carcinoma will take this route of spread. Mark, 1977 & Scanlon,
1980).
Melanoma and lymphoma of the head and
neck have been reported to be disseminated through the perineural
route. Stout, in 1949 remarked upon the tendency of epithelial tumors
to involve the regional nerve and regarded the perineural space as
potential source for distant spread of the disease. The time between
the primary lesion or recurrence with perineural metastasis can be
quite long, especially the adenoid cystic carcinoma. (Marsh et al,
1979). Recurrence with perineural metastasis without local recurrence
at the primary site can occur. The incidence of perineural spread
vary: adenoid cystic carcinoma approximately 50-60%; epithelial
carcinoma 5-14%, basal cell carcinoma, and melanoma, approximately 5%.
(Carter, 1983; Goepfert, 1984; Ballantyne, 1963). The trigeminal,
facial, and hypoglossal nerves are commonly involved. (Goepfert,
1984).
Scattered references appeared in
medical literature, and the presentation has rarely shown in detail.
Dodd et al in 1970 describe the mechanism of spread, the anatomy of
the cranial nerves most amenable to radiologic exploration, and the
roentgen signs of this form of metastatic disease. With advances in CT
and MRI, the earlier detection of perineural metastasis through the
base of the skull has become readily attainable. (Crawford et al,
1989). On CT scans, the lesion can be well demonstrated, especially
when it confines to the bony foramen and canal. On MR images, the
T1-weighted image reveals the extent of the lesion and T2-weighted
image demonstrates tissue characteristics of the lesion. The lesion
may show low signal intensity on T1-weighted image and low to
intermediate signal intensity on T2-weighted images, but on
post-contrast images, the lesion is often enhanced with high signal
intensity.
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END OF
SCIENTIFIC EXHIBIT "Perineural Metastasis to The Cranial
Nerves in Head and Neck Malignancies." |
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