Abstract
Purpose. This article reports on a sclerosing perineal-perianal rhabdomyoma in an adult woman. A review of the literature disclosed no reference to this histological form of rhabdomyoma in women. Methods and Results. We describe the case of a 48-year-old woman. At physical examination, a firm nodular lesion was identified in the left lateral perianal-perineal region. Histologically, it comprised rounded and elongated muscle fibers displaying no evident atypia, within a stroma exhibiting marked sclerosis and mild lymphoid infiltrate. At immunohistochemical examination, tumor cells stained for desmin, muscle-specific actin, and myogenin. Conclusions. Skeletal muscle rhabdomyomas are rare benign tumors, generally divided into 3 major categories depending on their clinical and morphological characteristics: fetal, adult, and genital. An unusual histological variant of the genital form has recently been reported in men, characterized by the presence of predominantly mature muscle fibers and marked sclerosis. We document such a lesion in a female patient for the first time.
Introduction
Rhabdomyoma is a benign tumor of striated muscle. Depending on the muscle affected, rhabdomyomas are classified as cardiac or extracardiac. Extracardiac or skeletal muscle rhabdomyomas are generally subdivided into 3 major categories: fetal, adult, and genital. 1 Fetal rhabdomyoma, the most common form, presents in children as a circumscribed sessile or pedunculated mass composed of myotubules and occasional differentiated myoblasts within a myxoid stroma; mitotic figures may be frequent, but cytological atypia and invasive margins are not seen. Adult rhabdomyoma, generally occurring in older adults, presents as a well-circumscribed nodular mass composed of mature muscle fibers with a vacuolated eosinophilic cytoplasm (“spider” cells); rod-like inclusions or cross-striations may be observed. Both fetal and adult rhabdomyomas exhibit a predilection for the head and neck, and are more common in males. Genital rhabdomyoma, the least common form, most often occurs in girls and middle-aged women. Most cases in women present as polypoid lesions of the cervix or vagina, comprising strap-like rhabdomyoblasts arranged in a loose or hyalinized stroma. 1 Genital rhabdomyomas in men tend to arise from the spermatic cord, epididymis, tunica vaginalis, or paratesticular soft tissues.2-13 Although most genital rhabdomyomas resemble the adult and fetal forms,2-10 an unusual variant has recently been reported, characterized by marked stromal sclerosis.11-14 Regardless of their location and morphology, rhabdomyomas lack malignant potential, and complete excision is curative; local recurrence is in most cases due to incomplete excision. 1
Material and Methods
Case Material
A 48-year-old woman was referred with proctalgia, pruritus ani, defecatory difficulties and progressive growth of a palpable perianal nodule of several years’ standing. At physical examination, the nodule was evident as a firm, painless mass located in the left lateral perianal-perineal region. Abdominal and pelvic computed tomography scan revealed a pelvic-floor lesion measuring 6 × 4 × 5 cm, close to the posterior vaginal wall and involving the anal sphincter (Figure 1). The surgical specimen excised (7.2 × 3.5 × 1 cm) contained a well-circumscribed mass measuring 6.5 × 3 cm with a uniform trabeculated cut surface.
Contrast-enhanced abdominal and pelvic computed tomography scan showing pelvic-floor lesion measuring 6 × 4 × 5 cm, involving anal sphincter, levator ani, vagina, and urethra. There is some loss of distinction between these structures.
Results
Histopathology
At histological examination, the mass was found to comprise varying-sized striated muscle fibers—round, polygonal, or elongated—within a stroma displaying marked sclerosis (Figure 2A). Large round or polygonal cells were strongly predominant and exhibited an eosinophilic fibrillar cytoplasm; nuclei, sometimes multiple, were vesicular in appearance, with prominent nucleoli (Figure 2B). Mitotic figures were occasionally observed (<1/50 high-power field; Figure 2C). The sclerotic stroma contained lymphoplasmacytic infiltrate generally forming lymphoid clusters, and trapped nerve fibers which in some cases displayed perineural hyperplasia (Figure 2D,3A).
(A) Muscle fibers varying considerably in size, embedded in a sclerotic stroma. Cytoplasm eosinophilic and fibrillar; nuclei, sometimes multiple, are often vesicular in appearance, with prominent nucleoli (hematoxylin–eosin, 40×). (B) Elongated fibers interspersed among round and polygonal cells, some displaying nuclear chains (hematoxylin–eosin, 40×). (C) Scant mitotic figures (hematoxylin–eosin, 40×). (D) Low-magnification view of muscle lesion, showing marked stromal sclerosis and lymphoid clusters (hematoxylin–eosin, 10×).
(A) Stromal trapped nerve fibers, some displaying perineural hyperplasia (hematoxylin–eosin, 20×). (B) Overview showing intense cytoplasmic staining for desmin (IP, 20×). (C) Cells were occasionally positive for myogenin (IP, 40×).
Immunohistochemistry
At immunohistochemical examination, tumor cells stained strongly for desmin (Figure 3B); staining for muscle-specific actin was weaker and more irregular. Muscle-cell nuclei were occasionally positive for myogenin (Figure 3C). The lesion extended into surgical margins. Although margins were not widened, no recurrence was reported after 12-month follow-up.
Discussion
The histological features of this perineal-perianal tumor in an adult woman closely resemble those reported for paratesticular sclerosing rhabdomyoma, a tumor recently identified as an unusual variant of the adult rhabdomyoma, 14 characterized by the presence of isolated or clumped skeletal muscle fibers set in a sclerotic stroma containing irregular lymphoplasmacytic aggregates. It can be distinguished from the adult rhabdomyoma by its more heterogeneous cellularity, varying degree of morphological differentiation (round and polygonal forms), and the absence of “spider” cells. It can also be distinguished from the fetal rhabdomyoma by the presence of numerous large, mature muscle cells and by the prominent sclerosed stroma containing lymphoid infiltrate. 14 Focal myogenin expression should not be regarded as indicative of sclerosing rhabdomyosarcoma, since myogenin is expressed only by a small number of immature cells; moreover, the tumor reported here displayed none of the signs of malignance (nuclear pleomorphism, frequent mitosis, necrosis) characteristic of this rhabdomyosarcoma variant. 15
The unusual perianal location of this lesion in an adult is also striking: the few cases reported to date have all been fetal rhabdomyomas in children, marked by abundant myxoid matrix.16,17
Sclerosing rhabdomyoma should not be confused with rhabdomyomatous hamartoma, a congenital lesion most commonly occurring in the head (eyelids, chin, nose, lip, tongue) and neck,17-20 though occasionally reported elsewhere, including the sacral region 21 and the vagina. 22 Histologically, it comprises a haphazard arrangement of varying proportions of mature tissues, including adipose tissue, skeletal muscle, adnexal structures, and, less commonly, nerves and vessels.
In conclusion, this article reports on a sclerosing rhabdomyoma whose unusual clinical presentation has not previously been reported either in women or in the perineal-perianal area. Differential diagnosis of this clinical entity should include rhabdomyomatous hamartoma, which is usually congenital, and spindle-cell rhabdomyosarcoma, a malignant tumor that may also contain sclerotic stroma (sclerosing rhabdomyosarcoma).
Footnotes
Authors’ Note
This article complies with the ethical responsibilities laid down in the journal’s requirements: research procedures were in accordance with the ethical rules of the committee on human experimentation, and with the World Medical Association Declaration of Helsinki. The participants’ right to privacy and confidentiality was fully guaranteed; no identifying data were included in the text or images. Informed consent was obtained from all patients both for participation in the study and for the publication of the results.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.