Schwannomas are benign, solitary, encapsulated
neoplasms also known as neurilemmomas. They are
uncommon tumors that arise mostly from peripheral
nerves in relatively deep parts of the soft tissues such as
the posterior spinal root and the acoustic nerve;
extremities, trunk and neck being the most common
locations
6,7. Because of lacking schwann cells,
schwannomas do not arise from cranial nerves I and II
8. They arise from both peripheral and intracranial parts
of cranial nerves in head and neck region. The acoustic
nerve is the most common intracranial site whereas
peripheral cranial nerve schwannomas are usually
located in parapharyngeal space of the neck and in soft
tissues such as tongue, buccal mucosa, palate and
gingiva
9,11. In parapharyngeal space, the most
commonly involved nerves are the vagus and the
cervical sympathetic chain
12.
Schwannomas are characterized by solitary
occurrence, slow growth, and smooth surface6.
Clinical symptoms are variable and most schwannomas are typically asympomatic depending on the nerve of the
origin. If the original tumor is small it may not be easily
identified; however if the original tumor is large it grows
inside the epineural sheath and undergoes progressive
enlargement, with the nerve fasicles spreading out of the
surface of the tumor11. In most of the cases, the only
complaint is a painless mass. Schwannoma of the lip is a
rare clinical entity and it was first reported by Das Gupta
et al in 196913. Since 1965 a few number of
schwannoma cases of the lip have been reported4,14,15. Our report is on an extremely rare case which is a
schwannoma of the lower lip.
Histologically, the characteristic features for the
schwannoma of the lip are similar to those described for
analogues found at other sites. In the same tumor, two
characteristic patterns are described as Antoni A and
Antoni B areas. The relative proportions of two regions
may vary. Hypercellular Antoni A areas consist of
monomorphic spindle shaped schwann cells with pointed
basophilic nuclei and poorly defined eosinophilic
cytoplasm2,6,14. Antoni B areas consist of loosely
arranged cells and small cystic spaces. In Antoni B area,
cystic degeneration, vessels with thick hyaline walls and
hemorrage may be observed11,14.
Immunohistochemically, positive S-100 protein and lev-7
antigen reactivity warrants schwann cell nature of these
tumors1,4. Vimentin and glial fibrillary acid protein
staining can also be helpful16. For schwannomas of
the lip, ultrasound, computed tomography and magnetic
resonance imaging can be used for preoperative
diagnosis. Homogeneous, hypo echoic features and posterior acoustic enhancement are seen on ultrasound5. Computerized tomography shows homogeneous soft
tissue density mass with clear margins4. and magnetic
resonance imagining shows a homogenous lesion with
low intermediate signal intensity on T1-weighted images
and high signal intensity on T2-weighted images6.
Schwannoma may occur at all ages peak incidence
being in the second and third decades of life10. The
male to female ratio in schwannoma is 2/311. In our
case, schwannoma of the lower lip may have arisen from
an end branch of the mental branch of cranial nerve VII.
Radiological examination was not performed considering
the relatively small size of the lesion. For schwannomas,
conservative surgical removal is the choice of treatment,
wide excision is not recommented since the prognosis is
good and recurrence is rare8,14,15. Malign
transformation of schwannoma of the lip has been
controversial but a few isolated cases have been
reported in literatüre8,14,17.
Schwannomas are rare tumors with nonspecific
presentation so clinical diagnosis is difficult. Differential
diagnosis of such a lip mass must include fibroma,
pleomorphic adenoma and other salivary gland tumors16. Diagnosis is confirmed with histopathological
examination. In present case our initial diagnosis was
salivary gland tumor, however it turned out to be
schwannoma on pathological examination. Schwannoma
should be taken into consideration in the differential
diagnosis of a lower lip mass even though it is a rare
clinical entity.
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