Skeinoid fibers in mesectodermal leiomyoma of the ciliary body

Mesectodermal Leiomyoma of the Ciliary Body: A Unique Variant of Leiomyoma with Myogenic and Neurogenic Histological Features

Mesectodermal leiomyoma of the ciliary body is a rare benign tumor, showing both neurogenic and myogenic characteristics. This tumor typically shows predilection for women of reproductive age. Because it is almost impossible to clinically distinguish this tumor from malignant melanoma, unnecessary eye enucleations have been unfortunately performed. Herein, we report a case of mesectodermal leiomyoma of the ciliary body in a young Japanese woman. She was referred to our hospital due to a slow-growing mass in her left iris. A malignant tumor could not be clinically ruled out and surgery with intraoperative pathology consultation was performed. Intraoperative frozen section diagnosis was a benign tumor with neurogenic features, and a simple excision of the tumor was performed. Histologically, the tumor was composed of diffuse growth of spindle cells with fibrillary indistinctive cytoplasm. Immunohistochemical examination showed diffuse positive staining of α-smooth muscle actin, h-caldesmon, calponin, and CD56. Scattered tumor cells were weakly positive for desmin. Neither melanocytic markers nor neural markers except for CD56 were positive. We diagnosed this tumor as mesectodermal leiomyoma. Mesectodermal leiomyoma is rare and often misdiagnosed as malignant melanoma. To avoid overtreatment, a correct preoperative diagnosis is essential.

Acute Presentation of Mesectodermal Leiomyoma of the Ciliary Body

Purpose

We report a case of acutely presenting mesectodermal leiomyoma of the ciliary body in a 29-year-old female who reported waking up with swollen eyelids of the right eye and light-perception vision. The affected eye had elevated intraocular pressure, a flat anterior chamber, and a pale, round mass arising from the nasal ciliary body, invading the angle and protruding into the visual axis posterior to the lens. Within days, the visual acuity decreased to no light perception. The eye was enucleated.

Methods

The enucleated eye harbored a tumor arising from the ciliary body, measuring 18 mm in the greatest dimension. Spindled cells with fibrillary cytoplasmic processes suggested a neural origin though negative for S-100, Melan-A, and HMB-45. The cells stained strongly positive for smooth muscle actin and vimentin, leading to the diagnosis of mesectodermal leiomyoma of the ciliary body.

Results

We review the literature to expand upon the clinical findings, diagnostic methods, and histopathologic and immunohistochemistry characteristics of mesectodermal leiomyoma.

Conclusion

Leiomyoma must be in the differential diagnosis for ciliary body mass, especially in women of reproductive age. Diagnosis relies on histopathology and immunohistochemistry. The mechanism of acute symptom onset may be multifactorial. This case emphasizes the possibility of acute presentation of a rare, benign intraocular tumor.

Gastrointestinal stromal tumor: an ultrastructural investigation on regional differences with considerations on their histogenesis

Gastrointestinal stromal tumor (GIST) is the most frequent spindle cell tumor in the gastrointestinal tract and may arise from esophagus to rectum. The stomach is the most frequent site, followed by small intestine, rectum, and esophagus. There have been some regional differences reported in their histopathologic and clinical presentations. The purpose of this study is to compare ultrastructural features of GIST, according to its anatomic site, in order to provide additional data to support the current concept of its histogenesis. Fifty-four GISTs (27 from stomach, 23 from small intestine, and 4 from rectum) were included in the study. Histopathologically, gastric GISTs tended to be more frequently epithelioid, particularly those in children, while small intestinal GISTs (SISTs) were mostly spindly in all but three cases. All four of the rectal GISTs were spindly. Ultrastructurally, there seem to be considerable regional differences. In the majority of gastric GISTs, in both epithelioid and spindle types, tumor cells exhibited focal features of myoid differentiation evidenced by the presence of incomplete external lamina (EL) and/or focal accumulations of thin fibers with interrupted electron densities consistent with actin filaments. However, features of myoid differentiation were exceptional for SISTs and rectal GISTs, being present in only one example in each. Some gastric GISTs, particularly those having an epithelioid appearance, showed cell borders luxuriously decorated by long filopods (anemone cell features). Anemone cell features were also present in spindle cell types of gastric GISTs as well as SISTs, albeit it was simpler and less luxuriant. Skeinoid fibers were present in the majority of SISTs and rectal GISTs, but absent in all gastric GISTs except one. These differences appeared to be too significant to propose a uniform histogenesis for all GISTs. Nevertheless, on closer analysis, certain features could be identified to explain a line of differentiation in all GISTs ranging from (1) polygonal uncommitted epithelioid mesenchymal cells with cell borders decorated by luxuriant fimbria, to (2) spindly tumor cells with less prominent fimbria, or (3) cells with or without features of minimum myoid differentiation characterized by the focal presence of cytoplasmic actin fibers or incomplete EL or skeinoid fibers, which might represent an altered product of EL protein. These findings led the author to speculate that the probable primordial cells of GIST may be the primitive mesenchymal cells, which have the potential to differentiate into myoid cells. In this regard, it is important to note that the putative primordial cell of GIST, interstitial cells of Cajal (ICC), and intestinal smooth muscle cells have been shown to develop from the common progenitor cells of the primitive gut, and c-Kit plays a crucial role in the determination of their fate to differentiate to muscle cells or ICC. The author concludes that all GISTs derive from stem cells in the gut retaining some of the differentiation potential seen in primitive gut cells. One of the likely candidates for such cells in the intestinal musculature is ICC-DMP (interstitial cells of Cajal associated with deep muscular plexus) identified as ICC having smooth muscle features identified exclusively by electron microscopy. These cells have been shown to have some of the features of muscle cells by the presence of external lamina and less well-organized cytoplasmic filaments; they also express CD117 in the cytoplasm. Furthermore, recent studies demonstrated the presence of so-called progenitor cells of ICC, similar to ICC-DMP in appearance, expressing insulin-like growth factor and CD34, indicating their stem cell nature. The author proposes that all GISTs develop from the common progenitor cells similar to primitive gut cells, which may differentiate into tumor cells with more myoid features in the stomach (similar to so-called ICC-DMP) as well as spindle cells with less myoid features (similar to ICC-MP [interstitial cells of Cajal associated with the myenteric plexus] in the small intestine and rectum). ICC-DMP have been recruited in the group of ICC by electron microscopic technique alone without methylene blue stain and it is questionable whether they are part of ICC depicted by the ICC network originally shown by Dr. Cajal more than century ago. Recent discovery of their expression of insulin-like growth factors may indicate that they represent persisting primitive gut cells (gut stem cells), which may serve as the progenitor cells to GIST. It is also pointed out that in this era of ICC and GIST pandemonium, a minority of intestinal stromal tumors with mature smooth muscle features have been totally ignored; these now appear to belong to GISTs, representing the best differentiated example among the tumors developing from the same progenitor cells.

Stromal Elements for Tumor Diagnosis: A Brief Review of Diagnostic Electron Microscopic Features

Tumor diagnosis mainly depends on the appearance of the tumor cells in recapitulating the appearance of primordial cells from which they arise. However, certain tumors may present with specific stromal changes that may assist/enhance the diagnosis. In this presentation, diagnostic stromal features have been reviewed. The cytoplasm is enclosed by a unit membrane, which serves as a barrier to, as well as an interface with, surrounding structures. Epithelial cells usually show characteristic basal-apical orientation. In mesenchymal tissue, different types of interface can be found in different types of mesenchymal tissue. External lamina can be defined as an anatomic structure, which encloses anatomic functional units. In epithelial tissue, cells in a functional unit are enclosed within a well-defined external lamina (EL). In malignant epithelial tumors, EL can become increasingly indistinct as tumors become less differentiated, and one has to look for it diligently. Within the external lamina, epithelial cells are closely packed with closely apposed cell membranes and cell attachment junctions. In contrast to epithelial tissue, mesenchymal tissue is usually characterized by the stromal elements they produce. Individual cells are embedded in the stroma, and individual mesenchymal cells represent the functional unit. Vascular endothelial cells are an exception since their relationship to stroma resembles to that of epithelial cells. Thus, tumors deriving from mesenchymal cells known to have external lamina such as muscle cells and Schwann cells tend to show total enclosure of cells by external lamina. In malignant muscle tumors, external lamina production can be focally present and found only by diligent search. In Schwann cell tumors, the presence of EL is prominent in low-grade tumors and more irregular and variable in malignant tumors. In the latter, stromal aggregation of scrolls of external lamina can be characteristic. Similar features are seen in ossifying fibromyxoid tumors. Fibronexus junctions (composed of extracellular fibronectin fillements linking intracellular 5-nm filaments) is claimed to be typical of myofbroblasts. Finding them in spindle cell tumors justifies a diagnosis of myofibroblastomas. There have been several stromal changes diagnostic for certain tumors found only by electron microscopy. Fibrous long-spaced collagen (known as Luse bodies) is diagnostic for peripheral nerve sheath tumors, but they can rarely be found in other tumors. Luse bodies usually appear as focally as crystallized aggregates apart from the regular collagenous interstitial stroma. They should be distinguished from other nonspecific long-spaced collagen changes. The changes are diffusely stromal in contrast to Luse bodies. Spiny collagen and amianthoid fibers are interesting collagen fibrils and their diagnostic value is questionable. Skeinoid fibers (SF) are short-spaced collagen of 41- to 45-nm banding so-named because of their peculiar appearance by electron microscopy simulating skeins of yarn. They were originally described in neurogenic tumors and small intestinal stromal tumors with features of gastrointestinal autonomic nerve tumors (GANT). Although there have been a few sporadic case reports of the presence of skeinoid fibers in nonneurogenic tumors, the frequent presence of SF in spindle cell tumors signifies their neurogenic nature in this authors' experience. An exception to this is that SF can be a constant element of rare ciliary body tumors known as ciliary mesectodermal leiomyomas, in which tumor cells show some resemblance to smooth muscle as well as Schwann cells. In addition to SF, several other types of peculiar crystallized collagen were observed in GANT tumors, particularly those with multiple tumor syndromes such as neurofibromatosis and Carney's triad. They simulate the appearance of railroad tracks or centrosomes. The reason for this is not known. The authors speculate that such collagen crystallization may be caused by genetic alterations involving collagenosis. Further studies will be necessary to clarify their pathogenesis. Another peculiar stromal change is electron-dense stromal filamentous aggregates with extra-long banding of > 250-nm periodicity previously described in Ewing sarcomas. This stromal change simulating a tiger skin pattern is also seen in primitive neuroectodermal tumors and malignant melanomas. In view of continually new discoveries of stromal changes that can be used for the differential diagnosis of tumors, the importance of close evaluation of stromal elements of tumors, and diligent application of electron microscopy in tumor diagnosis cannot be overemphasized.

Unusual primary ocular neoplasm in a child: leiomyosarcoma of the ciliary body

Primary uveal-tract neoplasms are extremely rare in childhood; the most common lesions found are melanocytic. We report here the case of a 7-year-old girl who underwent enucleation of the right eye with clinical suspicion of choroid melanoma as a result of a ciliary body mass that extended to the posterior chamber. Histologically, the neoplasm featured spindle cell morphology, atypia, and mitoses. The tumor expressed smooth muscle alpha actin, pan-actin HHF-35, and desmin, whereas immunohistochemistry for melanocytic markers, such as S-100, Melan-A, and HMB-45, was negative. Based on these features, the diagnosis of leiomyosarcoma of the ciliary body was firmly established. Although several leiomyomas have been reported in the literature, there are only 2 previously reported cases of primary leiomyosarcoma of the uveal tract. Immunohistochemical expression of muscle proteins allowed distinction from the most common melanocytic tumors arising in this location.

Report of two cases of ciliary body mesectodermal leiomyoma: unique expression of neural markers

OBJECTIVE

Mesectodermal leiomyoma of the ciliary body is a rare tumor with, to our knowledge, only 15 cases reported in the literature. It has a neural histopathologic appearance and a presumed origin from neural crest.

DESIGN

Case report.

RESULTS

Two cases of mesectodermal leiomyoma with histopathologic and immunohistochemical confirmation are reported.

CONCLUSIONS

For the second time, we were able to demonstrate expression of neural immunohistochemical markers in this tumor.

Unusual uveal tract tumor: Mesectodermal leiomyoma of the ciliary body

Benign smooth muscle tumor, leiomyoma, can occur throughout the whole body, including the most common sites of the genitourinary and gastrointestinal tracts, less frequently in the skin, and rarely in the deep soft tissue or uveal tract. A 23-year-old Chinese woman presented with a 4 month history of a pigmented ciliary body mass in her left eye. The tumor's clinical appearance and ancillary data were initially consistent with malignant melanoma. However, instead of enucleation, sclerotomy with a tumor biopsy was performed because of the patient's young age and the possibility of benign tumors. Under light microscopy, tumor cells were short spindle- or ovoid-shaped with fine nuclear chromatin and fibrillary cytoplasmic processes resembling neural tissue. Although the tumor displayed neurogenic morphology, it showed strong reactivity for alpha-smooth muscle-specific actin and h-caldesmon, and was negative for neurogenic markers, except CD56, by immunohistochemistry. Primary mesectodermal leiomyoma of the ciliary body was diagnosed because of both the myogenic and neurogenic characteristics. The tumor biopsy or intraoperative frozen section is suggested for accurate pathological diagnosis before enucleation. In a review of the literature, only 14 cases have been reported. Seven cases (50%) were subjected to enucleation and eventually showed a benign mesectodermal leiomyoma. This case report provides novel expression of h-caldesmon and CD56 by the tumor cells of mesectodermal leiomyoma.

Transscleral resection of a ciliary body leiomyoma in a child: case report and review of the literature

PURPOSE

To present the case of a patient with leiomyoma of the ciliary body and discuss the histological features and treatment of this rare intraocular tumor. METHODS/CASE REPORT: A 13-year-old boy presented with an asymptomatic tumor of the right eye. Visual acuity was 20/20 in both eyes. Ophthalmoscopy revealed an amelanotic, vascularized ciliary body tumor with exudative retinal detachment and partial transillumination. On ultrasound examination the tumor height was 8 mm and a low internal reflectivity was found. T2-weighted MRI scans showed a hypointense and T1-weighted scans a hyperintense intraocular mass with significant Gd-TPA enhancement. On the assumption that the diagnosis was consistent with an amelanotic ciliary body melanoma, a transscleral resection with adjuvant ruthenium-106 brachytherapy was performed. Visual acuity was 20/40 at 6 months after the operation.

RESULTS

Routine stains revealed a pleomorphic tumor composed mainly of spindle cells with palisading in some areas and a prominent intercellular fibrillary background. Immunohistochemistry showed positivity for desmin, vimentin and actin. No reactivity with S-100 and HMB-45 was seen. Intracytoplasmatic filaments and micropinocytotic vesicles were detected by transmission electron microscopy. These findings were consistent with the diagnosis of a ciliary body leiomyoma.

CONCLUSION

Typical clinical features of leiomyoma include a dome-shaped configuration and translucency, but the final diagnosis can only be confirmed by histology with the aid of immunohistochemistry and electron microscopy. Though rare, leiomyoma should be considered in the differential diagnosis of amelanotic uveal tumors. Transscleral resection is the treatment of choice of anterior uveal leiomyomas, with a fairly good visual prognosis.

Anterior segment tumors: current concepts and innovations

The most common anterior segment tumors are primary neuroepithelial cysts, uveal melanomas, metastatic tumors, and benign tumors. In the majority of cases, the diagnosis can be made utilizing a careful clinical history and ocular examination. Ultrasound examination (low and high frequency) has become an indispensable tool used to determine tumor extension and involvement of the surrounding structures. In particular, high-frequency ultrasound has been used to uncover iris pigment epithelial cysts, to allow for the diagnosis of small ciliary body melanomas, and to measure tumors for plaque radiation planning. Whereas fluorescein angiography and computerized tomography have come to play a limited role, fine-needle aspiration biopsy has been found to be quite helpful in selected cases. Once the diagnosis is established, treatment decisions depend on the tumors' location, size, local extension, patterns of growth, and secondary complications. Most anterior segment tumors can be observed for growth prior to treatment. Other options include local resection (iridectomy, lamellar sclerouvectomy, or eye-wall resection) and radiation (ophthalmic plaque or external beam). Enucleation is typically employed if these eye- and vision-sparing treatments are not possible and for uncontrollable secondary glaucoma. This review examines the unique role of high-frequency ultrasonography for the diagnosis and treatment of anterior segment tumors as well as an overview of clinical practice.

Mesectodermal leiomyoma of ciliary body

A 37-year-old woman had a mass in her left ocular globe. Uveal melanoma was suspected and enucleation was performed. Microscopically, the lesion proved to be a typical case of mesectodermal leiomyoma of the ciliary body. According to some authors, the peculiar neural appearance of this tumor could be the reflection of its probable origin from mesectodermal smooth muscle. Immunohistochemical analysis showed reactivity for muscle-specific actin and negativity for desmin, S-100 protein, HMB-45, EMA, and GFAP. Our results do not support the proposed neuroectodermical origin of this tumor, since coexpression of muscular and neural markers was not observed.

Relationship between skeinoid fibers and stromal matrix in gastrointestinal stromal tumors: morphometric analysis with quick-freezing and deep-etching method

Our previous study of a gastrointestinal autonomic nerve tumor with skeinoid fibers (SF) using the quick-freezing and deep-etching method, suggested that the distance between one radix and a neighboring radix (DRNR) in pre-existing meshwork structures around the tumor cells is consistent with the periodicity of the SF. Therefore, measurement of the DRNR in the meshwork could clarify the significance of the pericellular matrix for SF development. In the present study, we analyzed the meshwork in three cases of gastrointestinal stromal tumor (GIST), which showed different immunohistochemical stainings, but confirmed to have smooth muscle differentiation (SMD) by immunohistochemistry and/or electron microscopy. The DRNR from the three cases of GIST showed similar histogram patterns (a peak of 20-30 nm, mean values of 28.02, 25.74 and 26.45 nm), which were significantly shorter than the periodicity of SF (a peak of 40-45 nm, mean value of 42.14). Although we need further studies with additional GIST cases, we speculate that the pericellular matrix of GIST with SMD is not suitable for SF development.

Type VI collagen immunoreactivity in skeinoid fibers in small intestinal stromal tumors

By immunoperoxidase analysis for types I to VI collagen, elastin, cytoskeletal components and some glycoproteins, we found type VI collagen immunoreactivity in amorphous eosinophilic deposits (skeinoid fibers) in three small intestinal stromal tumors. Negative results were obtained for types I, II, III, IV and V collagen, elastin, laminin, ubiquitin, intracellular filaments such as actin, desmin, vimentin, calponin and caldesmon, and glycoprotein such as lysozyme, factor XIIIa, beta2-microglobulin, alpha1-antitrypsin and alpha1-antichymotrypsin. In two lesions, the periodic acid-Schiff-positive skeinoid fibers were also focally labeled for amyloid P component.

Renal angiomyolipoma resembling gastrointestinal stromal tumor with skenoid fibers

We report an unusual case of renal angiomyolipoma occurring in 68-year-old man. The tumor lacked well-developed vascular and adipose components and was composed almost exclusively of smooth muscle cells. Numerous skenoid-like periodic acid-Schiff-positive globules were interspersed between the tumor cells; the lesion therefore closely resembled a low-grade stromal tumor of the gastrointestinal tract. The HMB45-positive/CD34-negative immunophenotype was essential for the diagnosis of angiomyolipoma. Neither gastrointestinal tumor nor any signs of tuberous sclerosis were found. This lesion should be included in the list of morphologic variations of angiomyolipoma, which may cause diagnostic difficulties.