Keywords
immunohistochemistry - laryngeal neoplasms - rhabdomyoma
Introduction
Rhabdomyomas (RMs) are rare lesions of striated muscle origin that can be found in
cardiac and in extracardiac locations. The latter can be divided into two distinct
categories: adult and fetal. Of these two, in the head and neck, the adult type is
more common. Laryngeal RMs are extremely rare, with only ∼40 cases being reported
worldwide.[1] Adult-type RMs show an absolutely benign behavior and never metastasize.[2] The treatment is excision. Recurrences are rare.
Review of Literature with Differential Diagnosis
Two forms of RM exist: cardiac and extracardiac. Extracardiac RMs represent true rare
neoplasms that contain muscle elements. Histologically, these tumors are subcategorized
into adult and fetal forms according to their degree of cellular differentiation and
maturity. Adult-type tumors are confined to the head and neck region and usually originate
from musculature of the pharynx, oral cavity, or less commonly the larynx. RM occurs
more frequently in men than women (4:1). The reported ages of affected patients have
ranged from 16 to 76 years.[3] Most reported cases of extracardiac RM have involved solitary masses. Approximately
3 to 10% of adult RMs may be multiple.[4] RM virtually has no malignant potential.
RMs of the larynx usually appear as mucosal covered masses that vary in size. They
frequently are asymptomatic solitary lesions but progressive hoarseness, a foreign-body
sensation, and airway obstruction may occur. Dysphagia is also a possible symptom.
The radiologic features are usually those typical of benign neoplasms, with well-circumscribed
margins with no invasion of surrounding tissue.[1] In a few cases, computed tomography (CT) findings may mimic the appearance of the
malignant lesions with indistinct borders and blending with adjacent isodense muscle
tissue. Magnetic resonance imaging is better at delineating RM from surrounding structures.
The differential diagnosis for laryngeal masses includes cysts, laryngoceles, malignant
neoplasms such as squamous cell carcinoma and rhabdomyosarcoma, as well as benign
neoplasms such as hemangiomas, lipomas, amyloidomas, neurofibromas, and granular cell
tumors.[5]
Histologic analysis is essential for diagnosis. Adult RM have been confused with many
other benign tumors as hibernoma, oncocytoma, tumor of salivary glands, paraganglioma,
and others,[6] but mainly with granular cell tumor.[1] Microscopically the adult RM is characterized by large, closely packed, elongated
to polygonal cells with pink to bright eosinophilic and finely granular cytoplasm.
The nuclei are round to oval, vesicular, usually peripherally located, but may be
centrally located. Prominent nucleoli are frequently noted. Cross-striations are characteristic
but are not an obligatory feature in light microscopic evaluation.[2] They are more easily seen with phosphotungstic acid hematoxylin staining. Ultrastructural
studies showed actin filament and Z bands.
The diagnosis of RM is histopathologic and can generally be well defined, but some
cases can cause difficulties. Immunohistochemistry (IHC) reactions are of particular
value in differentiating the similar lesions. The IHC features of RM are identical
to those of normal skeletal muscle cells because it shows positivity to MSA (muscle-specific
actin), desmin, and myoglobin.[6] The positivity of these muscular markers is consistent with RM, as well as the positivity
for vimentin, a marker of mesenchymal tissues.[2] The main lesion to be differentiated from RM is the granular cell tumor that morphologically
consists mainly of smaller cells, has no cross-striations, and is consistently positive
for S-100 protein but negative for all myogenous markers IHC preparations.[2]
RM treatment is surgical resection. This procedure should be as conservative as possible.
Local recurrence has been reported and usually results from incomplete resection.[5]
Case Report
The 35-year-old white man complained of progressive hoarseness during a 1-year period.
On indirect examination of the larynx, a large submucosal mass was noted in the left
supra glottic larynx ([Fig. 1]). The contrast-enhanced CT of the neck revealed a well-demarcated diffusely hyperattenuating
submucosal mass on the left supraglottic space ([Fig. 2]).
Fig. 1 The laryngeal bulky lesion.
Fig. 2 Computed tomography revealed a well-demarcated diffusely hyperattenuating submucosal
mass.
The patient was taken to the operating room where the mass was endoscopically dissected.
The histopathologic diagnosis was of polygonal cell neoplastic favorable to paraganglioma.
The pathologist strongly suggested the complementation with IHC studies. IHC stains
for desmin ([Fig. 3]) and vimentin (muscle and mesenchymal markers respectively) were positive. Markers
for epithelium membrane tumors and S-100 protein for neuroectoderm tumors were negative,
thus changing the diagnosis to RM adult type. At a careful revision of the slides,
the hematoxylin and eosin sections revealed neoplastic closely packed polygonal cells
with deeply eosinophilic vacuolated cytoplasm ([Fig. 4]). Nuclei were round, vesicular, centrally located, with prominent nucleoli. Intracytoplasmic
and intranuclear hyaline inclusions were seen. Cross-striations, not noted before,
were present in few cells ([Fig. 5]). Mitotic activity and necrosis were absent.
Fig. 3 Strong positive staining for desmin of adult rhabdomyoma (× 400).
Fig. 4 Histology of rhabdomyoma showing closely packed polygonal cells with deeply eosinophilic
vacuolated cytoplasm. (Hematoxylin and eosin, × 400.)
Fig. 5 Scarcely seen cross-striations. (Hematoxylin and eosin, × 400.)
The patient recovered well. His voice was normal after a period of 3 months. He is
free of recurrence at 15 months of follow-up ([Fig. 6]).
Fig. 6 The larynx aspect 15 months after endoscopic removal of the lesion.
Discussion
Certainly the adult-type RM of the larynx is an extremely rare benign tumor of myoblastic
origin. A literature review allows us to say that only ∼40 well-documented cases have
been reported until today worldwide. In the past, RM was confused with other similar
tumors, especially with granular cell tumors. This confusion is due to granular eosinophilic
cytoplasm that is common to both diagnoses, although they have a completely different
histogenesis. Another important observation of the histologic point of view is that
the RM should not be confused with rhabdomyosarcoma, which has a completely different
prognosis. The histologic diagnosis should be no problem if adequately prepared slides
are available, but as these tumors are very rare and many pathologists are not familiar
with this type of tumor, there are reports of substantial difficulties to diagnose
them on the first try. We present another case of laryngeal RM in a patient whose
diagnosis was not initially set. Although the clinical and pathologic findings should
be taken into consideration, we emphasize that IHC plays an important role in the
differential diagnosis.
Symptoms of laryngeal RM do not differ from those caused by other benign tumors of
the larynx, but one should keep in mind the possibility of local airway obstruction
when the patient complains of breathing difficulties.
The tumor is usually described as a submucosal mass with a smooth surface that can
resemble the appearance of a cyst. Laryngoscopy and imaging exams help locate and
define the limits of the tumor, but the definitive diagnosis will always depend on
the histopathologic studies.
The clinical outcome of laryngeal RM adult type is benign and no evidence of metastasis
was reported in the literature. Treatment should always be surgical removal, via either
endoscopic or external approach, but always preserving the adjacent structures such
as the vocal folds and the swallowing apparatus. Recurrence can happen but usually
is due to incomplete excision of the tumor.
Conclusion
Although muscle tumors of the larynx are very rare, the RM should be considered when
there is a submucosal mass in the larynx. Because the establishment of definitive
diagnosis can be difficult with routine histopathology, it is important to consider
the realization of IHC studies.
