Pacinian hyperplasia ("Pacinioma", pacinian neuroma) associated with meningoradiculocele.
Dysraphic conditions of the spine resulting from non-closure of the neural tube comprise a wide spectrum of different types of malformations. In meningoradiculocele the nerve roots are components of the herniated cystic structure. The material that usually is submitted to histological examination may contain various amounts of soft tissue (including adipose tissue) and meninges (1, 2, 5, 6). Nerve structures are frequently encountered and may vary from easily identifiable large myelinated nerve trunks to small nerve fascicles with moderately increased numbers of fibres compared to those normally present. Very rarely, these structures may present "neuroma-like" features with proliferation of Schwann cells, or pacinian corpuscles hyperplasia with "onion bulbs" features (1, 2, 5, 6). Hypertrophy and hyperplasia of pacinian corpuscles is a rare condition and occur mainly in adults (4, 7, 8). The preferential site of occurrence is the hand but some deep seeded localisations have been described (3, 8). Although history of local trauma was often reported, the pathogenesis of such a lesion is still unclear (8). Histologically, pacinian hyperplasia does not form large tumor-like masses. The corpuscles have a normal structure but are increased in size and number. Sometimes they are dystrophic, with several lamellar bodies within a single capsule.
In the differential diagnosis, other lesion consisting of intraneural proliferation of perineural-like cells may be considered. Intraneural perineurioma is characterized by a tumoral, fusiform segmental growth of nerve trunks and histologically composed by densely packed, EMA-positive perineurial cells which proliferate in pseudo-onion bulb whorls around thin axons (9). In our case, the areas showing densely packed cells could resemble a "perineurioma-like" architecture: however, the combined EMA negativity and S-100 positivity indicate that these elements are reactive Schwann cell rather than real perineural cells.
Other nerve sheaths lesions or tumors, including neurofibroma, schwannoma and traumatic neuroma, may present a perineural onion bulb-like structures but pure pacinian differentiation associated to nerve sheath tumors have not been demonstrated (3, 8).
In conclusion, pacinian hyperplasia may be rarely encountered in sample obtained from surgery for spina bifida malformations, and has not to be confused with other more common neoplastic lesions affecting the spinal cord region.
Acknowledgments: The authors want to thank Dr. R. Bickenbach (Bonn) for the prenatal ultrasound data.
Contributed by Marco Gessi, Martina Messing-Jünger, Andreas Röhrig, Gerrit H. Gielen, Torsten Pietsch, Frank K.H. van Landeghem