Epibulbar Proliferative Fasciitis, a Variant of Nodular Fasciitis: A Differential Diagnosis of Conditions With Focal or Diffuse Myxoid Stromas.

PURPOSE: To describe the clinical and pathologic features of a case of epibulbar proliferative fasciitis and to compare it with other focal or diffuse myxoid lesions. METHODS: A clinical, histopathologic, and immunohistochemical analysis was performed. The clinical history, photographic documentation, history, and referred slides were reanalyzed. Additional immunohistochemical stains were performed at our institution. RESULTS: A 68-year-old woman developed over a week a brightly vascularized and focally hemorrhagic placoid lesion on the temporal side of the OS. She had had earlier augmentation breast surgery that had been mistakenly initially reported to us to be for breast carcinoma. Hematoxylin- and eosin-stained reactions revealed microscopically a spindle cell lesion with an intact nonkeratinizing epithelium and a background myxoid stroma with prominent capillaries and a light dispersion of small T-cell lymphocytes. Most striking among the spindle cells were some widely separated large atypical cells. The atypical cells were cytokeratin positive, but an expansive panel of immunohistochemical stains for breast carcinoma was negative. The lesion was diagnosed as proliferative fasciitis and has not recurred after 1-year follow up. CONCLUSION: A rapidly evolving conjunctival lesion is unlikely to be a primary or metastatic carcinoma. In the current case, the large ganglioform or rhabdomyoblast-like cells displayed diffuse cytokeratin positivity, still consistent with a mesenchymal or connective tissue cell lineage. Cytokeratin expression has been a finding previously reported in connective tissue tumors and in lymphoma cells. While the current lesion clinically resembles a conventional nodular fasciitis, the presence of the large atypical cells can lead to the misdiagnosis of a sarcoma, which typically displays a much higher Ki-67 proliferation index in comparison with nodular/proliferative fasciitis.

Conjunctival Implantation Cyst in the Orbicularis Oculi Muscle: Review of a Possible Origin From Displaced Stem Cells With a Differential Diagnosis.

PURPOSE: To document a unique case of a corneal/conjunctival epithelial inclusion cyst located in the orbicularis oculi muscle with a comprehensive review of variant conjunctival cysts and simulating conditions. METHODS: Clinicopathologic case report with detailed histopathologic and immunohistochemical evaluation for cytokeratins combined with a tabulation of mimicking lesions and relevant literature citations. RESULTS: A 59-year-old man experienced severe blunt left periorbital trauma that resulted in a limbal partial-thickness corneal wound with an associated epithelial abrasion and a full-thickness eyelid laceration extending from the superior fornix to the margin. Several months after surgical repair of the eyelid a cyst appeared in the superior pretarsal skin. Histopathologic and immunohistochemical investigations supplied data suggesting that the cyst had a high probability of a corneoscleral limbal stem cell origin. Distinctive features of the lesion are contrasted with those of allied or simulating cysts. CONCLUSIONS: Stem cells are now believed to be located at the corneoscleral limbus, in the inferior fornix, in the medial canthal region, and at the eyelid margin where transitions from conjunctival epithelium to epidermal epithelium occur. Due to their replicative, hardy and robust nature, stem cells displaced to alien environments are most likely to survive and produce cysts. The cyst's corneal-type cytologic characteristics, the absence of goblet cells, and the expression of a broad spectrum of cytokeratin biomarkers in the current case give support to the proposal that limbal stem cells in the region of the corneal laceration were displaced to the eyelid orbicularis muscle and were responsible for this most extraordinary cyst. Comparison with other epithelial cystic linings lends further evidence for this conclusion.

Orbital Involvement by Biphenotypic Sinonasal Sarcoma With a Literature Review.

PURPOSE: To document a case of a biphenotypic sinonasal sarcoma that impinged on the orbit via a tumor-induced mucocele and review the previous literature devoted to this condition. METHODS: A clinicopathologic case report with detailed histopathologic, immunohistochemical, and radiological studies with tabulations of previously reported cases and immunohistochemical stains for ruling out mimicking lesions. RESULTS: A biphenotypic sinonasal sarcoma arose from the ethmoid sinus in a middle-aged man. The tumor induced a mucocele that bowed the medial orbital lamina papyracea into the orbit and caused diplopia and mild proptosis. The biopsy's dual positivity for S100 and smooth muscle actin together with positive paired box 3 immunohistochemical staining established the diagnosis of biphenotypic sinonasal sarcoma. CONCLUSION: Biphenotypic sinonasal sarcoma, which can involve the orbit in 25% of cases, is a rare head and neck malignancy that has only recently been described. Biphenotypic sinonasal sarcoma is a low-grade, locally aggressive, nonmetastasizing sarcoma displaying both neural and muscle differentiation. It is further characterized by rearrangements of the PAX3 gene with multiple fusion partners, most commonly MAML3 (Mastermind like transcriptional coactivator 3). It occurs predominantly in middle-aged women and exclusively in the sinonasal tract. However, it can spread throughout the central facial structures to invade the brain if not detected early. Ophthalmologists should be aware of this new entity to avoid delays in diagnosis and treatment. The previous literature devoted to this condition was reviewed and analyzed for clinical, radiological, histopathological, and immunohistochemical features. In circumstances where molecular testing is not available, paired box 3 immunohistochemical staining can be used as an alternative diagnostic marker. The current case is most unusual because the orbital findings were induced by a mucocele caused by the tumor that obstructed the sinus ostium. This produced diplopia without direct tumor invasion into the orbital fat.

Hereditary Palpebro-Gingival Fibrosis Syndrome.

This is a case report involving 3 siblings, ages 22, 21, and 3 years old, of consanguineous parents and Syrian descent with a particularly unique clinical phenotype and eyelid/gingival findings that have not been previously characterized. Full-thickness eyelid biopsies for 2 of the siblings were evaluated by ophthalmic pathology showed generalized fibrosis without any active destructive process or amyloid. Three of the 9 siblings were affected by this order with no familial history. Ophthalmic plastic surgeons should be aware of this new entity as genetic localization and further identification may help families affected by this disorder.

Multicameral Steatocystoma Simplex of the Caruncle.

A yellow cyst of the caruncle in a 68-year-old man displayed the characteristic sebaceous glands and sebocytes of steatocystoma within the cyst wall, with a unique configuration of multiple branching compartments. The cyst lining was of trichilemmal character, lacking a keratohyalin granular layer, and replicated the immunohistochemical characteristics of a previously reported caruncular steatocystoma with the exception of a positive trichilemmal marker, calretinin, in the present case. Four previous cases of caruncular steatocystoma have been described, only one of which incorporated immunohistochemical analysis. Steatocystoma develops from a sebaceous gland duct, which displayed in this case multiple chambers subdividing what is usually a single round lumen.

Conjunctival Actinic Granuloma: A Clinicopathological and Immunohistochemical Study With a Review of the Literature and a Differential Diagnosis.

PURPOSE: To document a case of actinic granuloma (AG) of the conjunctiva, provide an extensive histopathologic and immunohistochemical description, review previously reported cases, and supply a differential diagnosis. METHODS: Both a retrospective chart review and comprehensive literature review were performed. The distinctive histopathologic pattern of the current case was defined with histochemical and immunohistochemical stains (CD163, p63, and a Verhoeff-Van Gieson elastic stain). Clinical follow up was obtained. RESULTS: A granulomatous process composed of CD163-positive mononuclear epithelioid cells and multinucleated giant cells was characterized by displaced extracellular actinic-related elastic fibers to the base of the lesion. Small elastic fibers were phagocytosed in epithelioid cells. Pseudoepitheliomatous hyperplasia of the overlying squamous epithelium was present; p63 assisted in defining the squamous proliferation and highlighted its noninvasive nature. Conjunctival AGs, according to the literature review, occur almost exclusively in young females, clinically manifest as nodular foci with painless injection over the course of weeks, and histologically featured granulomatous inflammation and elastophagocytosis. The etiology of this entity is likely multifactorial, but its genesis revolves around actinic injury. CONCLUSION: AGs of the conjunctiva have likely been an underreported entity in the past. The authors' review underscores the importance of including conjunctival AGs in the differential diagnosis of painless, subacute injected masses of the perilimbal conjunctiva. While it is benign, histopathologically separating AGs from neoplasia and other mimickers such pinguecula, foreign body granulomas, allergic, or rheumatoid nodules is essential for optimal management.

Lacrimal Gland Intravascular Micrometastasis From a Human Papillomavirus-Driven Anorectal Squamous Cell Carcinoma With a Review of Metastatic Disease to the Lacrimal Gland.

PURPOSE: To document a unique case of anorectal squamous cell carcinoma that was metastatic to the microvasculature of the lacrimal gland in a patient with human immunodeficiency virus and to review previously reported cases of metastases to the lacrimal gland. METHODS: Both a retrospective chart review and comprehensive literature review were performed. The unusual histopathologic pattern of the current case was illustrated with immunohistochemical studies (CD31, D2-40, pancytokeratin, p16, and p63) and in situ hybridization studies for high-risk human papillomavirus types 16 and 18. RESULTS: The authors describe the first case of metastatic anorectal squamous cell carcinoma to the lacrimal gland. Only 24 cases of metastatic disease to the lacrimal gland have been reported, the majority from breast carcinomas. The metastasis did not form a macroscopic lesions, instead was composed of microscopic intravascular and intraparenchymal tumor deposits, a subtle phenomena. Immunohistochemistry confirmed the presence of the intravascular neoplastic cells. p16 served as a surrogate marker for human papillomavirus-associated squamous cell carcinoma and was confirmed with in situ hybridization for human papillomavirus 16 and 18. This testing, combined with the clinical history, defined the diagnosis and confirmed human papillomavirus as the tumor driver. CONCLUSIONS: Metastases to the lacrimal gland remain rare, but clinicians and pathologists alike must be attuned to the possibility of subtle microscopic foci of tumor as a pattern of metastasis in scenarios without a discrete mass-forming lesion, as this may portend a poor prognosis.

Adult Primary Capillary Hemangioma of the Sclera: A Previously Undescribed Entity With a Review of Epibulbar Vascular Lesions.

PURPOSE: The objective of this article is to document a unique case of a primary hemangioma and review epibulbar vascular tumors of the conjunctiva and episclera. METHODS: A case report with detailed histopathologic, histochemical, and immunohistochemical studies coupled with a comprehensive review of the relevant literature with a tabulation of previously reported epibulbar vascular lesions was performed. RESULTS: A vascular tumor developed in a 46-year-old woman over 2-3 months that histopathologically was located in the superficial third of the normally avascular sclera and was composed of capillary caliber vessels. CD31 and CD34 positivity established the vascular nature of the lesion. Despite its adult onset, the tumor was also glut-1 positive, a vascular characteristic of childhood capillary hemangiomas that will ultimately involute. Smooth muscle actin was positive in the endothelial cells and associated pericytes. An ectatic muscular vessel identified in the midst of the lesion was interpreted as an anomalous intrascleral branch of an epibulbar anterior ciliary artery, where it perforated the sclera in the vicinity of the insertion of an extraocular rectus muscle. It was deduced to be the source of the capillary proliferation. A literature review failed to identify any previously reported epibulbar vascular tumor that originated primarily in the sclera or secondarily infiltrated this ocular tunic. CONCLUSION: An adult primary capillary intrascleral neoplasm is described as the rarest of all epibulbar vascular tumors and in keeping with the exceptional status of the ocular endothelium was glut-1 positive. This lesion must be distinguished from an array of other common and esoteric epibulbar vascular conditions.

Ocular Adnexal Adenomatoid Sebaceous Gland Hyperplasia: A Clinical and Immunopathologic Analysis in Relation to the Muir-Torre Syndrome.

The purpose of this study is to codify the microscopic diagnostic criteria for ocular adnexal brow and caruncular sebaceous gland hyperplasias (pseudoadenomatoid) that distinguish it from an adenoma. Clinical records and photographs were critically reviewed and microscopic slides were stained with hematoxylin and eosin and immunochemically stained for adipophilin, androgen receptor, p16, p53, a spectrum of cytokeratins, Ki-67 and mismatch repair nuclear protein expression for MLH1, MSH2, PMS2, and MSH6. The patients and their close relatives had no history of cancer. Cytokeratin 7 and especially cytokeratin 17 highlighted the presence of ducts in the hyperplastic lesion, which are not present in adenomas. p16 and p53 were negative and Ki-67 immunostaining demonstrated similar low proliferation indices for normal and hyperplastic glands. The mismatch repair nuclear protein expressions were preserved in both lesions. Histopathologic misdiagnosis of adenomatoid sebaceous gland hyperplasia as an adenoma can lead to the impression of an association with the Muir-Torre syndrome. Cytokeratins 7 and 17 immunostaining can be helpful in highlighting compressed ducts that in exuberant sebaceous gland hyperplasias may lead to a diagnosis of an adenoma (in which ducts are absent). Negative immunostaining for p16 rules out a possible etiologic role of human papillomavirus in hyperplasias and the negative p53 staining indicates the lesions are not truly neoplastic. The preservation of mismatch repair nuclear protein expression rules out the likelihood of the Muir-Torre syndrome. The current cases convincingly establish that sebaceous hyperplasia is not associated with the Muir-Torre syndrome by both clinical findings and immunohistochemical testing.Two yellow lesions, from the brow and caruncle, were examined microscopically and immunohistochemically to establish the diagnosis of sebaceous gland hyperplasia and to rule out the Muir-Torre syndrome.

PD-L1 and PD-L2 Expression Levels Are Low in Primary and Secondary Adenoid Cystic Carcinomas of the Orbit: Therapeutic Implications.

PURPOSE: To determine if there is a biologic rationale for using checkpoint inhibitor drugs targeting programmed cell death ligand 1 (PD-L1) and PD-L2 in the treatment of adenoid cystic carcinoma of the orbit. METHODS: Twenty-three cases of adenoid cystic carcinoma involving the orbit (13 primary lacrimal gland, 5 secondarily extending into the orbit, and 5 unspecified) were examined histopathologically. Immunohistochemistry for PD-L1, PD-L2, and CD8 was performed. Charts were reviewed for clinical correlations. RESULTS: Expression of PD-L1 and of PD-L2 was overall low in adenoid cystic carcinoma (mean expression 1.4 ± 0.9 of 5 for PD-L1, mean 0.83 ± 1.1 of 5 for PD-L2), and tumor-infiltrating CD8-positive T-lymphocytes were sparse (mean 1.1 ± 0.51 of 3). Only 13 of the 23 (57%) cases expressed PD-L1 as a combined positive score ≥1 of cells. No associations were found between expression levels of these markers and patient sex, tumor site of origin, Tumor, Node, Metastasis stage, or patient outcome. A significant association was observed between stromal PD-L1 expression and tumor histopathologic subtype (p = 0.05), and between tumor PD-L1 expression and prior exposure to radiation (p = 0.03). CONCLUSIONS: Checkpoint inhibitor drugs may have limited impact in the treatment and clinical course of orbital adenoid cystic carcinoma based on the low frequency of CD8 infiltrate and low expression of PD-L1 and PD-L2. Pretreatment with radiation, however, may improve tumor response to checkpoint inhibitor drugs.

Steatocystoma Simplex of the Caruncle: Case Report and Immunohistologic Study.

A yellow cystic lesion of the caruncle in a 23-year-old woman proved to be a solitary steatocystoma, a rare occurrence in that location. While the histopathologic diagnosis was evident from clusters of sebaceous cells within the cyst wall, a panel of immunohistochemical stains further distinguished the lesion from a keratinous cyst. The most useful stains for differentiating the two conditions were carcinoembryonic antigen, epithelial membrane antigen, cytokeratins 17 and 19, and calretinin. Only three previous cases of caruncular steatocystoma simplex have been reported, none of which included immunohistochemical studies. The current findings support the origin of the cyst from the small duct that connects the unilobular sebaceous gland associated with vellus hairs to the follicular canal.

Orbital Nasal-Type Extranodal Natural Killer/T-Cell Lymphoma: An Ongoing Diagnostic Challenge Further Confounded by Small-Cell Predominance.

PURPOSE: To highlight the histopathologic diagnostic challenges of small-cell predominant extranodal nasal-type natural killer/T-cell lymphoma (ENTNKT) of the orbit. METHODS: Retrospective chart review and histopathologic study with immunohistochemistry and in situ hybridization of 3 cases. RESULTS: Three cases of ENTNKT presented to the Mass Eye and Ear emergency room as orbital cellulitis over 1 year. The first case was unusual in that there was a predominance of small cells, giving the ENTNKT the histopathologic appearance of a nonmalignant inflammatory process. This challenging case is juxtaposed alongside 2 other cases, which exhibited the more typical lymphomatous microscopic appearance. DISCUSSION: ENTNKT can extend into the orbit from the adjacent sinuses or rarely arise primarily in the orbit. A diagnosis is typically made with a biopsy. Occasionally, however, the histopathologic diagnosis can be elusive when a predominance of small lymphomatous cells that are virtually indistinguishable from non-neoplastic inflammatory cells is present. Demonstration of CD56 positivity by immunostaining and in situ hybridization for Epstein-Barr virus are essential in confirming the diagnosis. CONCLUSIONS: ENTNKT should be considered both in the clinical and histopathologic differential diagnoses of orbital infections and idiopathic inflammations (pseudotumor).

Small Benign Storiform Fibrous Tumor (Fibrous Histiocytoma) of the Conjunctival Substantia Propria in a Child: Review and Clarification of Biologic Behavior.

PURPOSE: A case of a small benign storiform fibrous tumor of the conjunctival substantia propria is described to clarify the category of fibrous histiocytoma. In addition, a comparison of the various spindle cell tumors of the conjunctival substantia propria is explored. METHODS: The patient underwent a complete tumor excision, and the specimen was analyzed by histopathologic and immunohistochemical investigations. RESULTS: A cellular mass, composed solely of spindle cells in a storiform pattern without a component of histiocytic cells, was found beneath an undisturbed nonkeratinizing squamous epithelium and was separated from the epithelium by a grenz zone of uninvolved collagen. The lesion was sharply demarcated but not encapsulated. The Masson trichrome stain revealed scant deposition of intercellular collagen. The reticulin stain displayed numerous and delicate wiry fibers between the tumor cells and encircling capillaries. The Alcian blue stain demonstrated faint positivity in the interstitium. Immunohistochemistry revealed positivity for vimentin, factor XIIIa, smooth muscle actin, CD10, and CD45. Negative stains were obtained for CD34, CD56, S100, desmin, and Ki67. CONCLUSIONS: The broad term of fibrous histiocytoma should be reserved for deep fibroblastic spindle cell tumors (e.g., those of the orbit) that display an aggressive behavior. More benign superficial spindle cell tumors of the dermis are now preferentially characterized as dermatofibromas. It is suggested that equally benign epibulbar tumors should no longer be designated as fibrous histiocytomas but rather as benign storiform fibrous tumors. Tumors completely composed of polygonal histiocytoid (epithelioid) cells that are CD34+ should be excluded from the benign storiform fibrous tumor category. Positive smooth muscle actin and factor XIIIa staining in conjunction with negative staining for CD34 and desmin in the current spindled tumor cells are findings consistent with those of cutaneous dermatofibromas. Both the epibulbar and dermal spindle cell lesions have displayed an indolent and nonaggressive behavior. Microscopically they contain a high proportion of dendrocytic stellate cells that are either factor XIIIa+ or XIIIa-. Given the anatomic differences between the dermis and conjunctiva, the term dermatofibroma is inappropriate for the current tumor; instead the term benign storiform fibrous tumor has been proposed for superficial tumors of the conjunctiva.

Angiofibroma of the Eyelid: A Rare Clinical and Histologic Variant.

A flesh-colored, supraciliary lesion of the left upper eyelid in a 47-year-old man was excised for cosmetic reasons. Histopathology and immunohistochemistry demonstrated CD34-positive benign spindle cells, factor XIIIa-positive dendritic cells, and CD163-positive histiocytes, all dispersed within a diffuse collagenous background. Prominent loose perivascular cuffs of fibroblastic cells and collagen surrounded small blood vessels. Interpreted as an angiofibroma, the histopathology bore resemblance to that of a single previously-reported forearm lesion termed a "dermal fibroma with a distinctive perivascular cell arrangement." The lesion represents the first eyelid example of an unusual variant of angiofibroma.

Osseous cavernous hemangioma of the superior orbital rim.

A 53-year-old male presented with a bony lesion over the superior orbital rim increasing in size over several months. CT imaging showed a circumscribed, osseous lesion involving the outer table of the right frontal bone and superior orbital rim with a honeycomb appearance. Anterior orbitotomy revealed an osseous lesion along the superior orbital rim with purple cavernous spaces. Histopathological examination demonstrated cavernous vascular channels with variably-sized lumens and variably-thickened vascular walls interspersed among bony trabeculae consistent with an osseous cavernous hemangioma.

Dermalive Facial Filler Granulomas Masquerading as Neurofibromas.

A 56-year-old woman presented with periocular nodules that were clinically suspected to be neurofibromas. Histopathologic examination of excised nodules revealed a pronounced granulomatous reaction to a foreign material that was composed of glossy polygonal palely eosinophilic fragments. These fragments were outlined in red with Masson trichrome, stained gray with the elastic stain, and were uniformly red with Gomori methenamine silver staining. The histopathologic appearance was consistent with a granulomatous reaction to Dermalive facial filler. Postoperatively the patient admitted that she had filler injections many years earlier in another country, and that nodules appeared 1 year after injection. Treatment with steroids, intralesional immunosuppressive agents and surgery had been previously attempted to eradicate the nodules. The literature pertaining to granulomatous reactions to Dermalive and related hybrid facial fillers is reviewed and treatment options are discussed. This report is the first to illustrate the unique histopathologic staining characteristics of Dermalive, which may be useful to ophthalmic pathologists in identifying this uncommon foreign material.

Histopathologic Findings of Linear Scleroderma Displaying Focal Trichiasis Secondary to Tarsal Thinning.

Linear scleroderma en coup de sabre with ophthalmic findings has been previously described in the literature on numerous occasions. A 57-year-old woman presented with focal trichiasis secondary to tarsal thinning, adjacent to a linear brow and forehead deformity consistent with linear scleroderma en coup de sabre. Cases of linear scleroderma en coup de sabre involving the eyelids have been reported, most often with madarosis, ptosis, or skin atrophy; however, to the authors' knowledge, this is the first reported case of linear scleroderma associated with trichiasis and involvement of the deeper eyelid tissues, particularly the tarsus.

Ellipsoid Smooth Muscle Tumor of the Lower Eyelid: An Exploration of Its Possible Origin.

Ocular adnexal smooth muscle masses/neoplasms are extremely rare. Such lesions are comparatively more common in the conjunctiva than in the orbit and are most unusual in the eyelid. A 58-year-old woman slowly developed over 4 months a firm, movable sausage-shaped lesion in the deep lateral half of the right lower eyelid. The lesion ran parallel to and above the orbital rim. At surgery, the lesion was located between the orbicularis muscle and the inferior orbital septum. The term ellipsoid is used descriptively and does not imply any particular biologic behavior. Immunohistochemical evaluation revealed smooth muscle actin and desmin positivity. Due to the ubiquity of small blood vessels and the absence of smooth muscle bundles in the potential space between the orbicularis striated muscle and the inferior orbital septum, venular smooth muscle emerges as a highly likely source for the lesion.

A Lacrimal Gland Choristoma of the Lacrimal Sac.

Choristomatous lacrimal gland tissue has been detected in many different sites of the ocular adnexa, but has never before been convincingly described in the submucosa of the lacrimal sac. A 77-year-old woman with epiphora had a biopsy of the sac wall preformed during a dacryocystorhinostomy that contained such a lacrimal choristoma. Zymogen granules were found in the cytoplasm of the secretory cells with the periodic acid-Schiff reaction. No mucus-producing cells, as found in normal sac submucosal glands, were detected using the Alcian blue, mucicarmine, and Gomori methenamine silver histochemical stains. Gross cystic fluid protein-15 positivity was demonstrated immunohistochemically. The clinical implications of this choristoma are explored.

Gelatin-Based Hemostatic Agents: Histopathologic Differences.

PURPOSE: To delineate the histopathologic appearance of gelatin-based hemostatic agents, Surgiflo, Gelfoam, and Floseal, which are used by ophthalmic plastic surgeons, and which may incidentally be found as foreign materials in histopathologic tissue samples. METHODS: Histopathologic analysis was performed with hematoxylin-eosin, periodic acid-Schiff, Masson trichrome, and elastin staining on tissue samples in which gelatin-based agents were found. To better characterize these materials, similar analyses were performed on in vitro samples of commonly used gelatin-based hemostatic agents. RESULTS: Surgiflo and Gelfoam are composed of small stellate pieces of gelatin with a smooth, homogeneous quality. In tissues, they are faintly positive with periodic acid-Schiff staining, amphophilic with Masson trichrome staining, and ink-black with elastin staining. Floseal has a distinctly different morphology of large rectangular sheets, yet almost identical in vitro staining properties. DISCUSSION: While the morphology of the gelatin-based hemostatic agents is consistent under various conditions, the staining properties of these materials differ based on whether they have been in contact with human tissue. CONCLUSIONS: Gelatin-derived hemostatic agents are best identified based on their morphologic characteristics. Elastin staining highlights these materials prominently within tissue samples and may be helpful in distinguishing them from other foreign materials.