Electron microscopy in histiocytosis X

Langerhans Cell Histiocytosis of the Nose and Maxilla: A Rare Presentation

Langerhans cell histiocytosis (LCH) is a disease characterized by localized and generalized proliferation of the histiocytes. It is a locally aggressive condition. The clinical presentation is highly variable and can range from isolated, self-healing skin or bone lesions to life-threatening multisystem disease. It can present as a unifocal or multifocal disease. The majority are present in the head and neck region, but the involvement of Paranasal sinuses is rare. Here we describe a 64-years-old female who presented with a slow-growing left nasal mass for 1 year. Evaluation of the patient was suggestive of malignancy, but the biopsy report turned out to be Langerhans cell histiocytosis; subsequently left, total maxillectomy was done. We hereby present a unique case of LCH with isolated nose and paranasal sinus involvement.

Comparative study of two re-embedding methods on the ultrastructure of corneal tissue

PURPOSE

To expand the routine of pathological diagnostics of surgical keratoplasty specimens via transmission electron microscopy. The target was to identify the best re-embedding method for optimal structural preservation of formalin fixed paraffin embedded (FFPE) corneal tissue re-embedded into resin for ultrastructural analysis.

BASIC PROCEDURES

Bovine FFPE corneal tissue was re-embedded into resin with either a rapid osmium-free four-hour-method or a four-day-routine-method known from nephropathology, compared with primary resin embedded bovine corneal tissue. The analysis involved the ultrastructure of cytoplasm, the intercellular interfaces of superficial epithelial cells, deepest basal epithelial cells and corneal endothelial cells, cell matrix interfaces, Bowman layer, corneal stroma, its microfibril bundles and Descemet membrane.

MAIN FINDINGS

The main observation was the equally reduced preservation status of re-embedded FFPE corneal tissue independent of the used re-embedding method. This extends to the intercellular contacts of superficial epithelial cells and the apical tight junctions of corneal endothelial cells. Hemidesmosomal cell matrix contacts showed less demarcation in re-embedded specimens. Cell matrix interfaces of Bowman layer and Descemet membrane were more clearly bordered in primary resin embedded than re-embedded tissue. In contrast, gap junctions in re-embedded tissue were detected in deepest basal epithelial cells and corneal endothelial cells with comparable preservation to primary resin embedding. Bowman layer, corneal stromal extracellular matrix, its microfibril bundles and Descemet membrane showed equal ultrastructural preservation in all evaluated methods.

PRINCIPAL CONCLUSION

Corneal tissue can be successfully analysed with transmission electron microscopy after a rapid osmium-free four hour re-embedding procedure from FFPE material. A comparable morphology with primary resin embedded material can be obtained for gap junctions of deepest basal epithelial cells and corneal endothelial cells, further for Bowman layer, corneal stromal extracellular matrix, its microfibril bundles and Descemet membrane.

Myeloid, mast cell, histiocytic and dendritic cell neoplasms and proliferations involving the spleen

Splenic involvement and consequent splenomegaly are usually seen as part of systemic involvement by myeloid neoplasms as well as mast cell and histiocytic neoplasms. Primary splenic involvement by these neoplasms is rare. Splenectomy is usually not performed for establishing a diagnosis of these entities. However, in rare instances, the pathologist may need to evaluate the spleen secondary to splenic rupture or palliative splenectomy to alleviate symptoms related to splenomegaly. This review article describes the clinicopathologic features of a broad group of myeloid, mastocytic, and histiocytic proliferative and neoplastic disorders.

BRAFV600E mutant protein is expressed in cells of variable maturation in Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is a clinically and histologically heterogeneous disorder. Its classification as either reactive inflammatory or neoplastic has been a matter of debate. However, the recent finding of frequent BRAFV600E mutations in LCH argues for the latter. The exact cell type that harbors the mutation and is responsible for proliferation remains to be identified. We here apply a BRAFV600E mutation-specific antibody to detect the BRAF mutant cells in lesions from 89 patients with LCH. We found BRAFV600E mutations in 34 of 89 (38%) lesions. In lesions with the BRAFV600E mutation, the majority of cells coexpressing S-100 and CD1a harbored mutant BRAFV600E protein. These cells also expressed CD14 and CD36, whereas various fractions exhibited CD207. On the other hand, CD80 and CD86 expression was also present on BRAFV600E-positive cells. Thus, cells of variable maturation, exhibiting an immunohistochemical profile compatible either with myeloid cell or with dedifferentiated Langerhans cell antigens, carry the BRAFV600E mutation. In conclusion, we identify and characterize the neoplastic cells in LCH with BRAFV600E mutations by applying a mutation-specific marker and demonstrate feasibility for routine screening.

Recent advances in the understanding of Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is a proliferative disease of cells that share phenotypic characteristics with the primary antigen presenting cells of the epidermis. Its clinical manifestations are highly variable, extending from very benign forms to a disseminated, aggressive disease that causes significant mortality. Although many of the fundamental pathogenetic features of LCH have been enigmatic, recent advances have led to a much clearer understanding of the disease. In particular, careful molecular analyses of mouse models and human LCH samples suggest that LCH's cell of origin may not be the epidermal LC itself but a myeloid-derived precursor. Advanced genomic technologies have revealed the presence of activating, somatic BRAF mutations in the majority of patient specimens. Together, these observations have produced a new picture of LCH as a myeloid neoplasm. These advances are likely to have profound implications for the use of targeted therapeutics in LCH.

Histiocytic lesions involving the bone marrow

Histiocytic lesions involving the bone marrow include a number of reactive and neoplastic disorders. This article discusses the morphologic, immunophenotypic, and genotypic features of a variety of diseases associated with histiocytes and/or monocytes. Lysosomal storage disorders and hemophagocytic syndromes are often first diagnosed by bone marrow examination. Granulomas involving the bone marrow may also be the first indication of a systemic disorder. Apart from acute and chronic monocytic leukemias, the bone marrow is rarely involved by malignant histiocytic disorders, of which Langerhans cell histiocytosis is the most common.

Coexistence of localized Langerhans cell histiocytosis and cutaneous Rosai-Dorfman disease

Rosai-Dorfman disease (RDD; sinus histiocytosis with massive lymphadenopathy) and Langerhans cell histiocytosis (LCH) are two different yet pathogenetically related histiocytic disorders. While systemic and localized forms have been identified in both diseases, each has its own characteristic histological, immunohistochemical and ultrastructural profile. Rarely, either RDD or LCH can also occur in the context of certain malignant neoplasms. However, the coexistence of RDD and LCH has never been described. We report a case of cutaneous RDD in which a focus of LCH was found. Clinical and laboratory examinations revealed no evidence of extracutaneous involvement of RDD or LCH. We believe that this is the first report of such a coexistence, and the possible pathogenesis is discussed.

Splenic myeloid metaplasia, histiocytosis, and hypersplenism in the dog (65 cases)

Splenectomy specimens from 65 dogs with severe, diffuse, sustained, and progressive splenomegaly were examined. The clinical signs, hematology, and serum chemistry values in for the dogs were not useful diagnostic features. Microscopic changes in the spleens were distinctive and consisted of 1) myeloid metaplasia, 2) histiocytosis, 3) erythrophagocytosis, and 4) thrombosis with segmental infarction. Ultrastructural features suggested proliferative changes in the splenic reticular cells and macrophages (reticular meshwork) that described a continuum from reactive changes associated with immunologic damage of erythrocytes to neoplastic proliferation of histiocytic components. Thirty percent of the dogs survived 12 months. Approximately one half (53%) of the dogs with complete postmortem evaluations showed multiorgan involvement with a tissue distribution and cell morphology consistent with histiocytic neoplasia. For the remaining dogs (47%), only splenic pathology was consistently present, and a specific cause of death was often not evident. Distinctive histologic changes in the splenic tissues-including mitotic activity, erythrophagocytosis, giant cell formation, thrombosis/ infarction, and the proportion and distribution of histiocytic and hematopoietic cells-were statistically evaluated for prognostic relevance. The presence of giant cells was the only reliable prognostic feature, and that was indicative of a fatal outcome. These descriptive changes of myeloid metaplasia in the canine spleen are compared with the human clinical and pathologic syndromes of 1) agnogenic myeloid metaplasia, 2) hemophagocytic syndromes, and 3) hypersplenism. These diseases in humans produce histopathologic changes in the spleen that are similar to those observed in the canine splenic tissue we examined in this study.

Langerhans' cell histiocytosis and juvenile xanthogranuloma of the orbit. Clinicopathologic, CT, and MR imaging features

The clinical, radiologic, and histopathologic features of two main disorders of the orbit are discussed. Group I, Langerhans cell histiocytosis (histiocytosis X, Class I), is caused by proliferation of X histiocytic Langerhans' cells. Group II is juvenile xanthogranuloma, and Class II is related to the proliferation of non-X histiocytic (monocyte-macrophage) cells. The two diseases are of unknown cause and differ in their clinical, radiologic, and histopathologic features.

Nosology and pathology of Langerhans cell histiocytosis

The pathology of LCH is continuing to be defined and diagnostic features clarified as unprecedented research is done. Although the etiology of LCH remains unknown, new information on cytokines, viruses, immunologic dysfunction, cell surface antigen expression, and clonality in the disease are providing essential pieces of the puzzle.

Langerhans cell histiocytosis research. Past, present, and future

This article reviews the various investigative events that led to the endorsement of the term Langerhans cell histiocytosis for the various clinicopathologic conditions previously called Hand-Schüller-Christian disease, Abt-Letterer-Siwe disease, eosinophilic granuloma of bone, and histiocytosis X. The different denominations reflect the changing conceptual approaches to the so-called reticuloendothelial system and the successive acquisition of new ultrastructural and immunocytochemical data.

Hepatic nodules as single organ involvement in an adult with Langerhans cell granulomatosis. A case report

Liver involvement manifesting as hepatomegaly in Langerhans cell granulomatosis (LCG) is well known, but the definitive diagnosis is generally possible because other organs are involved. We report a 41-year-old white man who presented with cholestasis and liver nodules as an isolated hepatic LCG. The diagnosis of LCG was suspected based on routine histopathologic examination; the diagnosis became definitive 4 years later when Birbeck granules were found in the liver, an uncommon occurrence in this organ. This is an unusual presentation of a benign form of this disease and one of the first that reported Birbeck granules in the liver.

Histopathology of the liver in histiocytosis syndromes

Liver biopsies were studied in 47 cases representing various histiocytosis syndromes. These included 32 cases of hemophagocytic syndrome, 11 cases of Langerhans cell histiocysis (LCH), and 4 cases of other histiocytic disorders. All cases of hemophagocytic syndrome, except one with cytomegalovirus infection, displayed portal lymphohistiocytic infiltrates dominated by T lymphocytes. Activation of the hepatic mononuclear phagocytic system (MPS), evidenced by enlarged von Kupffer cells, some of which were hemophagocytic, was seen in 28 cases of hemophagocytic syndrome. Endothelial enlargement, minor degrees of hepatocellular degeneration, and steatosis were also noted. Ten of the 11 cases of LCH also showed activation of the MPS. It was the only lesion in two biopsies. Seven cases demonstrated nonspecific "triaditis." In three this was associated with cholangiocentric and random acinar histiocytic lesions. Evidence of activation of the MPS was also observed in both cases of Rosai-Dorfman disease and was accompanied by acinar histiocytic lesions in one and triaditis in the other. Likewise, both cases of juvenile xanthogranuloma showed activation of the MPS and focal granulomatous lesions. It is concluded that activation of the MPS is a common feature of liver disease in histiocytosis syndromes and that hepatic enlargement may be the result of this process instead of, or in addition to, the liver lesions known to be featured in these disorders. Hepatic lesions of the various histiocytosis syndromes resemble typical lesions in other sites and, in some instances, are accompanied by nonspecific changes. These nonspecific changes may occur in the absence of lesions that are diagnostic or typical of the particular histiocytosis syndrome. The location and character of hepatic lesions are important factors in the significance of liver involvement.

Ultrastructural studies in Langerhans cell histiocytosis: a search for evidence of viral etiology

The ultrastructure of lesional cells in biopsy material from 50 cases of Langerhans cell histiocytosis (LCH) was studied for the effects of virus and/or cytokines. Viral "footprints," which actually represent ultrastructural signs of the effects of cytokines on cells, were found in 76% of the cases. These were detected in lesional Langerhans cells, endothelial cells, and lymphocytes and consisted of tubuloreticular structures, cylindrical confronting cisternae, and curvilinear membranous formations. No virus particles or virus-specific cell products were found. These studies suggest that LCH cells are subject to cytokine stimulation but provide no evidence to implicate a virus in the disease process.

Fine-needle aspiration biopsy of Langerhans histiocytosis (histiocytosis-X)

A series of 14 fine-needle aspiration biopsies (FNAB) from histologically proven cases of histiocytosis-x (Hx) were reviewed. The smears revealed a variable mixture of Langerhans cells, eosinophils, macrophages, polymorphonuclear cells, and giant cells. Based on the predominant cells present, the cases were further categorized as Langerhans cell predominant (nine cases), eosinophil predominant (two cases), and macrophage predominant (three cases). Langerhans cells were usually polygonal without significant evidence of phagocytosis and frequently contained indented nuclei. In three cases, several Langerhans cells showed prominent dendritic processes. Electron microscopy in 10 cases revealed Langerhans cells with varying degrees of morphologic differentiation. All cases studied revealed Birbeck granules. These findings indicate that FNAB may be an effective technique for diagnosing Hx.

Sinus histiocytosis with massive lymphadenopathy--isolated suprasellar involvement

An unusual case of an isolated histioproliferative lesion arising from the suprasellar region is described. The presence of lymphophagocytosis suggested that this represented an extranodal intracranial form of sinus histiocytosis with massive lymphadenopathy.

Extracellular deposition of eosinophil major basic protein in orbital histiocytosis X

Although eosinophils are prominent in orbital lesions of patients with histiocytosis X (Langerhans' cell histiocytosis), little is known of their pathogenic significance in the disease. To determine whether eosinophils degranulate and deposit toxic proteins in orbital histiocytosis X, the authors examined lesions by indirect immunofluorescence for localization of the core granule protein (major basic protein) outside of eosinophils. Four patients with histiocytosis X were studied: three with eosinophilic granuloma and one with Hand-Schüller-Christian disease. Tissue eosinophilia was prominent in all specimens; striking extracellular deposition of eosinophil major basic protein was noted in three patients, and focal deposition was present in the fourth patient. Orbital specimens obtained at autopsy from patients without orbital disease were studied as control specimens; no tissue eosinophilia or deposition of eosinophil major basic protein was observed. These findings indicate that eosinophils likely degranulate in lesions of orbital histiocytosis X and may participate in the pathogenesis of the disease.

Immunohistochemical and ultrastructural study of histiocytosis X and non-X histiocytoses

The diagnostic reliability of ultrastructural and immunohistochemical examinations on routinely processed biopsy specimens of cutaneous histiocytic proliferations (histiocytosis X, n = 7; juvenile xanthogranuloma, n = 4; necrobiotic xanthogranuloma, n = 2; traumatic granuloma of the tongue, n = 1) was evaluated. S-100 protein, peanut agglutinin, and the antibody Mac-387 were used as markers for histiocytes. The frequency of Birbeck granule-containing cells in seven histiocytosis X lesions did not correspond with the number of S-100+ or peanut agglutinin+ cells. All neoplastic histiocytosis X cells were positive for S-100 protein and peanut agglutinin but were negative for Mac-387. Histiocytes of juvenile xanthogranuloma, necrobiotic xanthogranuloma, and traumatic granuloma were strongly positive for Mac-387 but were negative for S-100 protein and peanut agglutinin, except for the peanut agglutinin-reactive Touton giant cells. Mac-387 reliably differentiates histiocytic proliferations of the monocyte/macrophage system from those of the dendritic cell system. For the diagnosis of histiocytosis X, both S-100 protein and peanut agglutinin positivity in histiocytes is as reliable as ultrastructural demonstration of Birbeck granules.

Monoclonal antibody MT1: a marker for Langerhans cell histiocytosis

Langerhans cells and their pathologic counterparts can be identified in paraffin sections using immunohistochemical staining for S-100 protein. This procedure is useful in confirming a diagnosis of Langerhans cell histiocytosis (LCH). However, many other cell types are also positive for S-100 protein. Positive staining for CD1 (Leu 6) supports a diagnosis of LCH, but requires frozen tissue. A panel of antibodies would be desirable in confirming a diagnosis of LCH, particularly if these antibodies could be used on paraffin-embedded material. We studied the pattern of staining for commercially available monoclonal antibodies MT1, MT2, MB2, and LN1, which were originally marketed as lymphocyte markers, using paraffin-embedded tissue sections of cases of LCH. In all 20 cases pathologic Langerhans cells stained positively with MT1 only. Various other S-100 protein-positive lesions were also examined with MT1 and were consistently negative for MT1. Other cutaneous histiocytic and mast cell lesions were positive with MT1, but S-100 protein negative. Our results demonstrate that the monoclonal antibody MT1 serves as an additional marker for LCH and, together with S-100 protein, would make up a diagnostic panel of antibodies for LCH to be used on routine paraffin-embedded sections.

Eosinophilic granuloma of the cavernous sinus and orbital apex in an HIV-positive patient

A 35-year-old HIV-positive woman with painful ophthalmoplegia, sensory loss extending to all branches of the trigeminal nerve, and progressive optic neuropathy was found to have eosinophilic granuloma of the cavernous sinus, superior orbital fissure, and orbital apex. There was no radiologic evidence of a lytic bone lesion within the skull or orbit and clinical evidence suggested a primary intracranial origin for this lesion. This is the first case of a cavernous sinus syndrome caused by eosinophilic granuloma and the first time HIV infection is reported in association with histiocytosis-X.

Electron microscopy of large cell undifferentiated and giant cell tumors

Electron microscopy is a valuable morphologic method for the diagnostic evaluation of undifferentiated tumors composed of polygonal or oval large cells and mononuclear or multinucleated giant cells. Although few ultrastructural details are pathognomonic, electron microscopic findings may add significantly to the formulation of the final diagnosis if used in the context of other pathomorphologic and clinical data. Contributions of electron microscopy to tumor diagnosis are summarized and illustrated with appropriate examples from personal experience in a routine university hospital laboratory.

Urticating histiocytosis: a mast cell-rich variant of histiocytosis X

Histiocytosis X and mastocytosis are proliferative processes that may have similar cutaneous manifestations. However, a positive Darier's sign (urtication on stroking of the lesion) is thought to reliably distinguish between these two diseases. We recently studied a 13-year-old girl with a 2-year history of extensive skin lesions and a positive Darier's sign. Routine histopathologic studies revealed a polymorphous cutaneous infiltrate composed of histiocytes, mast cells, eosinophils, and lymphoid cells. Electron microscopic studies demonstrated Langerhans granules in some of the histiocytes, and immunologic studies of frozen tissue showed that a significant subpopulation of the histiocytes marked as Langerhans cells. Giemsa staining of specimens from eight other cases of cutaneous histiocytosis X from our files revealed mast cells in all of the lesions, although none showed the abundance of mast cells present in the case with urtication. Our studies emphasize the often polymorphous nature of the cell population in cutaneous histiocytosis X and demonstrate that confusing clinical findings can result when the mast cell population in histiocytosis X produces urtication.

S-100 protein immunohistochemistry and electron microscopy in the diagnosis of Langerhans cell proliferative disorders: a comparative assessment

To better define the roles of S-100 protein immunohistochemistry and electron microscopy in the diagnosis of Langerhans cell proliferative disorders, a comparative assessment of the two techniques was performed using material from 39 cases of histiocytosis X and 2 cases of infantile self-healing reticulohistiocytoma. Both techniques proved highly reliable, but neither alone enabled diagnostic confirmation in all instances. The two techniques proved complementary and used together did enable identification of Langerhans-type histiocytes in all cases studied. Neither was judged clearly superior and both offered certain advantages. Electron microscopy was found overall to be a slightly less sensitive technique, but more specific and less subject to misinterpretation. The S-100 stain was found to be particularly useful in situations where sampling problems were likely to be encountered or where the available specimen was otherwise suboptimal for electron microscopic examination. Because the S-100 stain is the more cost-effective to employ, we now recommend it for the purpose of providing routine diagnostic confirmation. In an investigative setting, however, we continue to recommend electron microscopy as the primary technique.

Massive metastatic pulmonary calcification in an infant with aleukemic monocytic leukemia

An 18-month-old infant with aleukemic monocytic leukemia and osteoclastic bone resorption demonstrated in the pelvis, vertebral bodies, and ribs developed severe refractory hypercalcemia. Bilateral interstitial pulmonary radiopacities developed rapidly, accompanied by hypoxemia and hypercapnea. Von Kossa staining of an open lung biopsy revealed extensive, finely granular metastatic septal calcifications not apparent on H&E-stained sections. Autopsy revealed the massive nature of the pulmonary calcinosis and the presence of additional calcifications in the atrial subendocardium, liver, kidneys, vessels, and skin. Metastatic pulmonary calcification has been infrequently described in infants, and premortem detection of such deposits has been rarely reported. The Von Kossa stain is useful in detecting minute pulmonary calcifications which may radiographically simulate infiltrates of infectious origin.

Significance of X granules in histiocytosis X: an ultrastructural study

Histiocytosis X is characterized by the presence of cytoplasmic rod structures called Langerhans' cell granules or X granules (XG). It has been speculated that histiocytosis X is a Langerhans' cell disorder. This ultrastructural study was performed to quantitate the number of XG containing histiocytes in the histiocytosis X lesions. Twenty-four specimens from 22 patients with histiocytosis X were studied: 4 from skin, 5 from lymph node, 11 from bone, 2 from lung, 1 from gingiva, and 1 from cheek. The majority of the histiocytes in histiocytosis X lesions do not contain X granules. The majority of the histiocytes in histiocytosis X lesions do not contain X granules. The percentage of histiocytes with XG in a lesion has no relation to the age of the patient or the organ from which it was obtained, except for skin, where they were quite numerous. The relative percent-age of histiocytes with granules does not correlate significantly with the prognosis of these patients.

Langerhans' cells and macrophages in eosinophilic granuloma. An enzyme-histochemical, enzyme-cytochemical, and ultrastructural study

Biopsy material of six patients with eosinophilic granuloma (EG) was investigated by electron microscopic and enzyme-histochemical methods for acid phosphatase (AcP), leucyl-beta-naphthylamidase (LA), adenosine triphosphatase, and alpha-naphthyl-acetate esterase (NE). Paraplast sections were used for demonstration of lysozyme with an immunoperoxidase method. Results of staining for these different enzymes suggested the existence of two separate sets of histiocytic cells: one type with "dot-like" AcP staining and negative for NE and lysozyme; and the other with diffuse AcP staining, positive for NE and lysozyme, and often showing signs of phagocytosis. The first type presumably represented Langerhans' cells and also often showed positive staining for LA. Macrophages were generally negative for LA. Electron microscopic study confirmed the impression gained from enzyme-histochemical studies. No intermediate cell types between Langerhans' cells and genuine macrophages were seen. From these results it is concluded that in EG no transformation exists between Langerhans' cells and macrophages. The latter are presumably of reactive nature.

Histiocytosis X cells and Langerhans cells: enzyme histochemical and immunologic similarities

The proliferating cell in histiocytosis X has been thought to be an abnormal Langerhans cell since the identification in 1965 of the characteristic X-bodies morphologically identical to the Birbeck granules of epidermal Langerhans cells. This conclusion is based primarily on this finding and on morphologic similarities at the light microscopic level. Enzyme histochemical data have been somewhat conflicting and have not provided strong support for this conclusion. Recently, immunohistochemical studies have shown data consistent with a Langerhans cell origin for histiocytosis X cells. This study documents the presence of nonspecific esterase, acid phosphatase, and adenosine triphosphatase in both Langerhans cells and histiocytosis X cells. Both types of cells also react with antibodies directed against widely distributed leukocyte antigens (HLA-A,B,C; Ia; L3B12); Langerhans cell/thymocyte antigen [Leu 6(T6)]; histiocyte antigen (Leu-M3); helper T-cell/histiocyte antigen [Leu-3(T4)]; and S-100 protein. These results complement earlier immunologic studies and add enzyme histochemical data that strongly support the concept of histiocytosis X as a proliferative disorder of cells of Langerhans lineage.

An unusual form of endoplasmic reticulum in mononuclear cells of a giant cell tumor of bone

A peculiar configuration of endoplasmic reticulum (ER) was observed by electron microscopy in some mononuclear cells from a malignant giant cell tumor of bone that had been removed from a cervical vertebral body in a 54-year-old female. The unusual ER consisted of looped, smooth tubules, which originated from poorly developed rough ER present in the tumor cells. The tubular structures were approximately 23 nm in diameter and contained paracrystalline material. The curvilinear tubular ER closely resembles the vermiform tubular structures that have been observed mainly in histiocytes from different clinical forms of histiocytosis X.

Histiocytosis X

To clarify salient issues pertaining to histiocytosis X--a syndrome that includes Letterer-Siwe disease, Hand-Schuller-Christian disease, and eosinophilic granuloma--the authors review the epidemiologic data and the histologic, morphologic, and clinical bases for diagnosis and prognosis. Histiocytes are defined and their possible histogenesis outlined, and Langerhans cells, which may be a leading element in active lesions, are characterized. The authors outline hypothetic pathogenetic schema, which they recommend be tested by recently developed immunologic and genetic means, since histiocytosis X, at least in its disseminated form, remains an unpredictable disease for which there is no proven effective therapy.