Soft tissue sarcomas are relatively rare tumors constituting
about 0.7% of all malignant neoplasms. Leiomyosarcoma
is the malignant tumor of smooth muscle cell origin.
It represents only 2-8% of all sarcomas and is found most
commonly in the gastrointestinal and female genital tract.
Other origins such as viscera, major arteries, veins &
extremities are less common sites. Leiomyosarcoma of the
head and neck region is very uncommon with only a few
cases at the various anatomic sites e.g. sino-nasal tract, oral cavity, mandible, larynx, trachea, hypopharynx, cervical
lymph node, external auditory canal and middle ear, etc.
have been mentioned in the literature. So far, only 8 cases
of leiomyosarcoma of the parotid gland have been reported [
2-
7].
Although the origin of leiomyosarcoma was thought to
be smooth muscle cell, several authors have proposed that
this tumor may, in fact be derived from pleuripotential,
uncommitted mesenchymal cells or smooth muscle cells
of blood vessel origin [8-12]. This implies that the origin
of this tumor was a small blood vessel within the parotid
tissue. The tumor might also have originated in the myoepithelial
cells that are capable of multidirectional differentiation.
As the whole parotid gland was replaced by the
tumor, it is very difficult to point the source of origin of
the tumor within the parotid gland.
Early cervical lymph node metastasis in head and neck
leiomyosarcoma is rare. Leiomyosarcoma is apparently
not a lesion with a high distant metastatic potential. Metastatic
spread of leiomyosarcoma is usually via hematogenous
route to lungs and observed in 20% of cases. Scalp metastasis,
as reported in our patient has not been mentioned from
leiomyosarcoma originating from any region and organ of
the body or any histologic variety of a parotid malignancy
in the literature. The patient developed a solitary metastasis
in the scalp region 15-months after the treatment for her
primary lesion. It is difficult to explain the exact mechanism
of such metastatic presentation. Malignant cells reach the
skin by a variety of the mechanisms including direct
extension, lymphatic or hematogenous spread and through
implantation in surgical scars. The so-called direct extension
is spread of tumor through tissue planes, while not an actual
metastasis to the skin, these tumors are included by some
authors in studies of skin metastasis. The lymphatic metastases
are believed to be the result of tumor cells spreading
through dermal lymphatics with the subsequent deposition
of the tumor cells in the skin. Distant metastasis as also
seen in the present patient seems to be the result of hematogenous
spread, which may involve the skin at distant
site from the primary lesion. Due to normal pulmonary
vascular bed filtering mechanism, distant metastases first
involve the lungs in approximately 75% cases. The lungs
were radiologically uninvolved in our patient. The alternative
pathway could be the spread via Batson's plexus, a route
of hematogenous metastases seen in various malignancies,
which bypass pulmonary circulation [13]. It is also possible that, altered lymphatic drainage following initial surgery
and radiotherapy for primary disease in the parotid gland
could have played a role in our patient, because the metastatic
site in the scalp was not very far away from the
primary site in the parotid gland.
Scalp lesions may manifest clinically in several forms
such as inflammatory lesions, discrete nodules or plaques.
Cutaneous metastases may vary in number from a single
nodule, as noted in our patient, to greater than 20 nodules
in various cancers.
Cutaneous metastases including scalp lesions from
various primary malignancies are rare. They are usually
associated with widespread disease and carry an extremely
poor prognosis. But the present patient had responded excellently to the treatment and currently she has no
evidence of disease 4 years and 9 months after the diagnosis
of her scalp metastasis.
Solitary skin metastasis in the scalp region from
primary leiomyosarcoma of the parotid gland (under control),
is an extremely rare feature of distant metastatic
presentation in the natural history of parotid malignancy.
The scalp lesion, 15-months after the treatment of primary
lesion in the parotid gland could have been clinically
misdiagnosed as second primary skin or another soft tissue
malignancy. Proper history, thorough clinical and radiological
evaluation and biopsy are necessary to establish the
diagnosis.
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