A 66 year-old man presented with slight difficulty
swallowing. Endoscopy revealed fullness in the posterior pharynx, and CT scan confirmed the presence of
a mass in this region. Fine needle aspiration biopsy was performed, and the mass subsequently resected.
The specimen consisted of a 4.5 x 4.0 x 2.0
cm. diameter circumscribed slightly lobulated soft piece of red brown tissue. Sectioning showed a solid
cut surface without necrosis or hemorrhage.
Case 1 - Figure 1 - Scanning magnification showing sheets of large cells with abundant eosinophilic cytoplasm.
Case 1 - Figure 2 - Mixture of large epithelioid cells with eosinophilic cytoplasm admixed with cells showing optically clear cytoplasm.
Case 1 - Figure 3 - Higher magnification showing cells with abundat eosinophilic cytoplasm and longitudinal cytoplasmic striations.
Histologically, large polygonal cells in solid sheets are focally interrupted by thin bands of
fibrous connective tissue, and dilated veins. The voluminous amount of deeply eosinophilic cytoplasm is
this tumor's most distinctive feature. Cytoplasm is variably coarsely granular or smudged, and often
contains cross striations. In some cells, striations are separated from each other at regular intervals
perpendicular to the long axis of the cell imitating mature skeletal muscle, while in others striations
are of irregular thickness and haphazardly placed within the cell. Coarse vacuolization is another
cytoplasmic feature of these cells. In areas this vacuolization is so pronounced as to produce a
microcystic pattern. So-called "spider cells" are formed by thin strands of cytoplasm separating
peripherally placed vacuoles. Nuclei are rounded and uniformly sized. Most have vesicular chromatin and
a single enlarged nucleolus, which is more or less centrally placed, within the cell. Mitotic figures
are exceedingly rare to absent.
Diagnosis - Rhabdomyoma, Adult-type
Rhabdomyomas are divided into two major categories –
cardiac and extracardiac. The latter is further divided into adult, fetal, and genital tract types.
Rhabdomyoma [ AR] is the most common subtype of rhabdomyoma even though it
remains relatively rare. A wide age range is affected from children (rare) to the elderly; most patients
are middle age (x=50 years) with a male predominance [as much as 4:1]. AR is a slow growing solitary
benign tumor with a predilection for sites in the head and neck. The larynx, oropharynx, and floor of
mouth are principally involved; rare examples have been reported in the soft tissues of the neck, orbit,
stomach, and esophagus. Clinical manifestations include primarily the discovery of a mass, but some
patients complain of hoarseness, and difficulty swallowing. About one-fifth of cases are reported as
multifocal. Excision is curative for AR, although local recurrence is possible if incompletely excised.
Gross findings show a circumscribed mass (usually less than 10 cm.) whose surface may be coarsely
bosselated. Occasionally the mass may be multinodular. These have a brick-red color resembling the
renal cortex. Histologic features are those described above. AR is so characteristic by light
microscopy that special stains and immunohistochemistry are unnecessary to establish a diagnosis in most
cases. Nonetheless, histochemical staining with Masson's trichrome or PTAH [phosphotungstic acid
hematoxylin] highlights the cross striations. Cell vacuoles are PAS-positive, diastase sensitive and
secondary to leaching of glycogen during tissue processing. Cells react with myogenic markers – muscle
specific actin, desmin, smooth muscle actin, myoglobin – as well as vimentin and and occasionally S-100,
but lack staining with epithelial antibodies [cytokeratin, EMA]. Ultrastructure shows the features of
incomplete skeletal muscle differentiation.
FNA cytopathology shows large polygonal cells in both clusters and single cells. Abundant finely
granular cytoplasm with parallel arrays of cross-striations is distinctive. Nuclei are regular, round to
oval and generally eccentrically placed in the cell. Unlike sarcolemmal nuclei of mature skeletal
muscle, nuclei of AR are generally single, rounded, and much larger without a characteristic linear
arrangement at the myofiber periphery.
Differential diagnosis of AR includes a number of benign and malignant neoplasms that harbor a
copious amount of cytoplasm. Among these are granular cell tumor, alveolar soft part sarcoma,
paraganglioma, malignant melanoma, and oncocytoma. Granular cell tumor [GCT]
has the same predilection for head and neck sites - tongue, oropharyngeal submucosa, soft tissue, and
larynx – as adult rhabdomyoma. GCT consists of sheets or nests of monomorphic polygonal cells with low
N/C ratio, round nuclei and abundant coarsely granular PAS +, diastase resistant cytoplasm. FNA
aspirates show cells in a loose syncytium with indistinct cell borders. The coarsely granular cytoplasm
is often better seen in Papanicolaou than in MGG stained smears. Immunophenotypically GCT is
consistently positive for S-100, vimentin, and CD68; negative with cytokeratin, actin, myoglobin, desmin,
and HMB-45. Congenital epulis is a clinicopathologic variant restricted to the anterior alveolar ridge
of newborn infants; females >> males.
The head and neck region (orbit, oropharyngeal mucosa, tongue) is a common site of Alveolar Soft Part
Sarcoma [ASPS]. This rare tumor more often affects adolescents and young
adults. Sharply outlined cell nests that are relatively uniform in diameter and separated by thin
fibrovascular septa produce an organoid (pseudoalveolar) growth pattern. A loss of cell cohesion leads
to wide spacing among cells in the center of these nests. Cells of ASPS are large, polygonal with
abundant eosinophilic finely granular cytoplasm. Relatively monotonous vesicular nuclei harbor a single
prominent nucleolus. Immunostaining shows variable positivity with vimentin, S-100, cytokeratin, and
actin; negative for EMA, desmin, myoglobin, myogenin. Aspirates reveal cells identical to those seen in
tissue - large polygonal epithelioid cells distributed in loose clusters. These possess cytoplasm that
is described as finely granular, reticular or frothy. Large oval nuclei have finely granular chromatin
and a single prominent macronucleolus. It is rare to find the nested pseudoalveolar pattern on smears
Paraganglioma [PG] is usually a benign neoplasm (5% are malignant) derived
from the extra-adrenal parasympathetic nervous system. The head and neck is among its most common sites.
Most PGs develop in middle age. Microscopic features include uniform sized chief cells [neuroendocrine
containing] in nests ("Zellballen" pattern) surrounded by inconspicuous sustentacular cells [unmyelinated
nerve fibers] and a rich capillary network. Chief cells are polygonal, rounded nuclei with moderate to
abundant finely granular eosinophilic, amphophilic, or oncocytic (rarely) cytoplasm. It is expected that
these cells will have scattered nucleomegaly and nuclear pleomorphism.
Rarely PG will display infiltrative sclerosis and spindle cell morphology. PG is negative with PAS
and mucin stains, consistently lacks cytokeratin staining, but is positive for neuroendocrine markers.
S-100 and GFAP are positive in the "sustentacular " cells. FNA smears show numerous bare nuclei, cells
in loose groups, moderate anisonucleosis, hyperchromic, rounded nuclei, and finely granular cytoplasm.
About 1% of cases of malignant melanoma [MM] arise in the sinonasal region. Other
non-orbital head and neck sites include larynx, and oral cavity, but rarely if ever in the nasopharynx.
An epithelioid (oncocytoid) appearance is one of the more common manifestations of MM, a tumor with a
broad range of architectural and individual cell features. Immunohistochemistry is positive for S-100,
HMB45 (gp100), melan-A, tyrosinase; staining for cytokeratin, and muscle markers is negative.
Extraparotid Oncocytoma may rarely arise in paranasal sinuses, larynx, and nasal
septum. These are solitary masses that develop in individuals older than 40 years. A nearly pure
population of oncocytes in an organoid, trabecular, or glandular pattern is present. Cells have abundant
deeply eosinophilic, finely granular cytoplasm with rounded uniformly sized nuclei and small nucleoli.
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