Oral leiomyoma case report

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1 Case Report Oral leiomyoma case report CHUAN-HANG YU 1 TUNG-CHIEH TSAI 1 HSIN-MING CHEN 2,3 CHUN-PIN CHIANG 1,2,3 1 Graduate Institute of Clinical Dentistry, College of Medicine, National Taiwan University, Taipei, Taiwan, ROC. 2 School of Dentistry, College of Medicine, National Taiwan University, Taipei, Taiwan, ROC. 3 Department of Dentistry, National Taiwan University Hospital, Taipei, Taiwan, ROC. Oral leiomyomas are rare and account for 0.42% of all benign tumors of the oral cavity. A typical leiomyoma can be diagnosed through examination of hematoxylin and eosin-stained tissue section by an experienced pathologist, but it is sometimes difficult to differentiate an atypical leiomyoma from a spindle cell soft tissue tumor and needs immunohistochemical stain for a confirmatory diagnosis. We reported a leiomyoma arising from the anterior floor of the mouth in a 59-year-old male patient. The mass measured cm. It was bilobular in shape, elastic in consistency, and covered by an intact, smooth, pink oral mucosa. Periapical radiography revealed no specific finding. The mass was totally excised under local anesthesia. Histopathologically, the tumor was well-demarcated and surrounded by a thin layer of fibrous connective tissue with minor salivary glands. It was highly cellular and composed of spindle-shaped cells that exhibited cigar-shaped nuclei and eosinophilic cytoplasm and were arranged in whirls and interlacing bundles. Mitotic figures were present but rare in number. Masson s trichrome stain showed red-stained muscle cells randomly dispersed in a light blue-stained stroma made up of collagen fibers. Immunohistochemically, the tumor cells were diffusely and strongly positive for myogenin and vimentin, moderately positive for smooth muscle actin and neuron-specific enolase, and weakly positive for actin, but were negative for desmin, myosin, myoglobulin, and S-100 protein. Many slit-like vascular channels in the stromal connective tissue were highlighted by the anti-cd31 and anti-cd34 immunostains. A solid leiomyoma was diagnosed. The patient was regularly followed up in the dental clinic. No recurrence of the tumor was found 3 months later. We suggest that an oral leiomyoma may need immunohistochemical stain with a panel of muscle-specific antibodies to confirm the histopathological diagnosis. (Chin Dent J, 24(2): , 2005) Key words: leiomyoma, oral cavity, immunohistochemistry. Leiomyoma is a benign tumor of smooth muscle origin that most often occurs in the uterus and gastrointestinal tract 1 and is rarely found in the oral cavity. The first case of oral leiomyoma was reported by Blanc in Oral leiomyomas account for 0.42% of all benign tumors of the oral cavity. The rare occurrence of the oral leiomyoma may be probably due to the paucity of smooth muscle found in the oral cavity 3. Received: March 18, 2005 Accepted: May 27, 2005 Reprint requests to: Dr. Chun-Pin Chiang, Department of Dentistry, National Taiwan University Hospital, No. 1, Chang- Te Street, Taipei, Taiwan 10048, ROC. Leiomyomas can be classified into three subtypes: solid leiomyoma, angiomyoma (vascular leiomyoma), and epithelioid leiomyoma (leiomyoblastoma, bizarre leiomyoma) 4, in which the angiomyomas are mostly encountered in the oral cavity 4-8. Although a typical leiomyoma can be diagnosed through examination of hematoxylin and eosin (H&E)-stained tissue section by an experienced pathologist, it is sometimes difficult to differentiate a leiomyoma from a neurogenic tumor or other spindle cell tumors and needs immunohistochemistry (IHC) for a confirmatory diagnosis. There were only few IHC studies on oral leiomyomas in the literature 1, In this article, we reported a leiomyoma arising from the anterior floor of the mouth in a 59-year-old 114

2 Oral leiomyoma male patient. Masson s trichrome stain and IHC with a panel of antibodies against myogenin, vimentin, smooth muscle actin (SMA), neuron-specific enolase (NSE), actin, desmin, myosin, myoglobulin, S-100 protein, CD31, and CD34 were used to confirm our histopathological diagnosis. CASE PRESENTATION This 59-year-old male patient was referred from a local dentist for treatment of an asymptomatic swelling at the anterior floor of the mouth opposite to the lingual side of teeth #31 and #32 (Figure 1A) for 16 months. The mass measured cm. It A B C D E F Figure 1. Clinical and histopathologic photographs of our leiomyoma. (A) Clinical photograph showing a mass at the anterior floor of the mouth opposite to the lingual side of teeth #31 and #32. (B) Low-power view demonstrating a well-demarcated highly cellular tumor (H&E, original magnification, 5 ). (C and D) Medium-power view exhibiting a highly cellular tumor surrounded by a thin layer of fibrous connective tissue with minor salivary glands (H&E, original magnification, 25 ). (E) High-power view showing spindle-shaped tumor cells with cigar-shaped nuclei and eosinophilic cytoplasm (H&E, original magnification, 50 ). (F) Masson s trichrome stain demonstrating red-stained muscle cells randomly dispersed in a light blue-stained stroma made up of collagen fibers (Original magnification, 50 ). 115

3 C.H. Yu, T.C. Tsai, H.M. Chen, et al. was bilobular in shape, elastic in consistency, and covered by an intact, smooth, pink oral mucosa. Periapical radiography revealed no specific finding. The clinical impression of the mass was a benign soft tissue tumor. It could be a fibroma, neurofibroma, neurilemomma, leiomyoma or rhabdomyoma. The patient s past medical history included a perforated duodenal ulcer which was treated by pyloroplasty and trunkal vagotomy 20 years ago and a nasopharyngeal squamous cell carcinoma (NPC) with neck lymph node metastases which was treated by irradiation (6040 rads divided into 51 doses for NPC and 5600 rads divided into 51 doses for neck metastases) approximately 18 years ago. The patient was regularly followed up at the Department of Otolaryngology. No recurrence of NPC was found. The patient was further referred to an oral and maxillofacial surgeon for total excision of the tumor. Under local anesthesia, the mass was removed and no bone destruction was seen during the surgical A B C D E Figure 2. Immunohistochemical staining of our leiomyoma. The tumor cells were diffusely and strongly positive for myogenin (A) and vimentin (B), moderately positive for smooth muscle actin (C) and neuron-specific enolase (D), and weakly positive for actin (E). (Original magnification, A, B, C, D, and E, 50 ) 116

4 Oral leiomyoma procedure. The specimen was subsequently sent for histopathological examination. Histopathologically, the tumor was well-demarcated (Figure 1B) and surrounded by a thin layer of fibrous connective tissue with minor salivary glands (Figures 1C and 1D). It was highly cellular and composed of spindle-shaped cells that exhibited cigar-shaped nuclei and eosinophilic cytoplasm (Figure 1E) and were arranged in whirls and interlacing bundles. Mitotic figures were present but rare in number. Masson s trichrome stain showed red-stained muscle cells randomly dispersed in a light blue-stained stroma made up of collagen fibers (Figure 1F). Immunohistochemically, the tumor cells were diffusely and strongly positive for myogenin (Figure 2A) and vimentin (Figure 2B), moderately positive for SMA (Figure 2C) and NSE (Figure 2D), and weakly positive for actin (Figure 2E), but were negative for desmin (Figure 3A), myosin (Figure 3B), myoglobulin (Figure 3C), and S-100 protein (Figure 3D). The slit-like vascular channels in the stromal connective tissue were highlighted by the anti-cd31 A B C D E F Figure 3. Immunohistochemical staining of our leiomyoma. The tumor cells were negative for desmin (A), myosin (B), myoglobulin (C), and S-100 protein (D). Slit-like vascular channels in the stromal connective tissue were highlighted by the anti-cd31 (E) and anti-cd34 (F) immunostains. (Original magnification, A, B, C, D, E and F, 50 ) 117

5 C.H. Yu, T.C. Tsai, H.M. Chen, et al. Table 1. Site distribution of oral leiomyoma in previous studies Authors Total cases Lips Tongue Buccal mucosa Palate Gingiva Others Baden et al % 18.3% 15.5% 15.5% 8.5% 14.8% Cherrick et al % 25.7% 20.0% 17.1% 5.7% 14.3% Natiella et al % 19.2% 17.8% 20.5% 4.1% 17.8% Praal et al % 20.8% 16.7% 20.8% 4.2% 22.2% Savage et al % 17.9% 23.1% 19.2% 3.8% 11.5% Epivatianos et al % 22.1% 19.1% 20.6% 4.4% 17.6% (Figure 3E) and anti-cd34 (Figure 3F) immunostains. A solid leiomyoma was diagnosed. The patient was regularly followed up in the dental clinic. No recurrence of the tumor was found 3 months later. DISCUSSION Oral leiomyomas are rare and account for 0.42% of all benign tumors of the oral cavity. Baden et al 8 reviewed the literature from 1884 to 1992 and found 142 cases of oral leiomyomas. The age of the patients ranged from 2 months to 85 years with a mean of 41 years. There was a slight male predilection (54.0%). The most frequently affected site was the lips (27.5%), followed in a descending order by the tongue (18.3%), buccal mucosa (15.5%), palate (15.5%), and gingiva (8.5%). There were some variations in the site distribution of oral leiomyomas in other reviews 5,7,12-14 (Table 1). The most prevalent site was found to be the tongue in 3 reviews 5,12,14. The second most common site was the palate in 3 studies 7,12,14 and the buccal mucosa in two 5,13. Furthermore, in third position were the buccal mucosa in 2 reviews 12,14, palate 5,13 in two, and the tongue in one 7. In sharp contrast with the findings of Baden et al. 8, the lips were in the fourth place in 3 reviews 5,12,14 and only 2 studies agreed that the lips were the most frequent site of occurrence 7,13 (Table 1). The discrepancies in the site distribution of oral leimyomas among these studies may be due to differences in the sample size, case selection criteria, and race of the patients. Clinically, most oral leiomyomas were asymptomatic, painless, and reported as a slow-growing mass with various sizes ranging from a few millimeters to 3 cm 1. The oral mucosa is rich in vascular supply and the smooth muscle is present in the tunica media of blood vessels. Therefore, the histogenesis of oral leiomyoma is believed to arise from the tunica media of the blood vessels. Other origins like circumvallate papillae 15, ductus lingualis 16, and heterotopic embryonal muscle tissue 17 have also been proposed. Oral leiomyomas are classified into three subtypes: solid leiomyoma, angiomyoma, and epithelioid leiomyoma 4. The most common subtype of oral leiomyoma is angiomyoma ranging from 60.0% to 75.6% in different studies 4-8, whereas the non-vascular subtypes (solid and epithelioid) range from 24.4% to 40.0% 4-8 (Table 2). A typical leiomyoma can be diagnosed through careful examination of H&E-stained tissue section by an experienced pathologist. Special stains such as Mallory s phosphotungstic acid hematoxylin (PTAH), Table 2. Subtype frequencies of oral leiomyoma in previous studies Author Total cases Vascular Non-vascular Case no. Percentage Case No. Percentage Enzinger et al % % Cherrick et al % % Galili et al % % Natiella et al % % Baden et al % % 118

6 Oral leiomyoma Table 3. The immunohistochemical staining results of previously reported oral leiomyomas and the present case Authors Case No. Myogenin Vimentin SMA NSE Actin Desmin Myosin MSA Myoglobulin S-100 Leung et al. 1 1 * * * * * * * * * - Baden et al. 8 3 * * * 0/3 * 1/3 * 3/3 2/3 0/3 Maeda et al. 9 1 * + * + * + * * * - Maeda and Osaki 10 1 * + * * * * - Lloria-Benet et al * * + * * + * + * - Yu et al * - - SMA = smooth muscle actin, NSE = neuron-specific enolase, MSA = muscle-specific actin Masson s trichrome, and van Gieson s techniques are also recommended for a proper diagnosis 9. The muscle fibers were stained blue with Mallory s PTAH, red with Masson s trichrome, and yellow with van Gieson s. In contrast, the intercellular collagen fibers were stained yellow to brick red with Mallory s PTAH, light blue with Masson s trichrome, and bright red with van Gieson s. Although these 3 special stains are helpful for the diagnosis of tumors of muscle cell origin, sometimes it is difficult to distinguish a leiomyoma from a spindle cell soft tissue tumor and needs IHC for a confirmatory diagnosis. We performed the Masson s trichrome stain to prove the muscle cell origin of our tumor. However, we could not confirm whether it was a leiomyoma or not. Therefore, we used IHC with a group of antibodies against myogenin, vimentin, SMA, NSE, actin, desmin, myosin, myoglobulin, S-100 protein, CD31, and CD34 to confirm our histopathological diagnosis. The IHC results of previously reported oral leiomyomas and the present case are listed in Table 3. The tumor cells of our case were strongly positive for myogenin and vimentin, moderately positive for SMA and NSE, and weakly positive for actin, but were negative for desmin, myosin, myoglobulin, and S-100 protein. Oral leiomyomas were also reported to be positive for desmin 8-11, myosin 10, and myoglobulin 8, although our tumor was shown to be negative for these three proteins. Two previous studies 8,11 demonstrated that oral leiomyomas are also positive for muscle-specific actin (MSA), but anti-msa stain was not available in our laboratory. All previous and the present IHC studies confirmed that oral leiomyomas are negative for S-100 protein 1,8-11. The anti-cd31 and anti-cd34 immunostains revealed many slit-like vascular channels evenly distributed throughout our tumor. These vascular channels were highly compressed by the tumor cells and became less prominent in an H&E-stained tissue section. The special stain and IHC findings prove the present case to be a solid leiomyoma. It is sometimes not easy to differentiate a leiomyoma from a low-grade leiomyosarcoma. It has been suggested that the distinction of leiomyosarcomas from leiomyomas is based on the concomitant presence of nuclear atypia, high mitotic index, and zonal necrosis in leiomyosarcomas. In addition, the presence of 10 or more mitotic figures per 10 high-power (400 ) fields indicates a malignancy, regardless of cellular atypism 18. Furthermore, if the tumor contains prominent nuclear atypia or large cells, 5 mitotic figures per 10 high-power fields are sufficient to justify a diagnosis of malignancy 19. It has been found that 20% of oral smooth muscle tumors reported in the literature are malignant 20, which is proportionally higher compared with the same lesions in the female genital tract. There were 2-3 mitotic figures per 10 high-power fields found in our case, but no atypical mitosis (i.e. tripolar or star-shaped mitoses), prominent cellular atypia, or any bizarre cells were seen. These microscopic features further indicate that our case is a benign solid leiomyoma. Oral leiomyoma is difficult to diagnose just based on examination of H&E-stained tissue section. It usually needs IHC for a confirmatory diagnosis. However, previous studies indicated that there were still some minor variations in IHC results of oral leiomyomas. Therefore, we suggest that an oral leiomyoma may need IHC with a panel of muscle-specific antibodies to confirm the histopathological diagnosis. 119

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