Light Microscopic Features Research Articles

Light and Electron Microscopic Features of the Kidney in Hedgehog (Hemiechinus auritus)

Kidneys are important organs that regulate the volume and composition of body fluids. In this study, some renal light and electron microscopic features were examined in 5 hedgehogs (Hemiechinus auritus). The right kidneys were processed for routine light microscopy, while the left kidneys were prepared for transmission electron microscopy. The kidney in this animal is bean-shaped and has a smooth surface. Light microscopy analysis revealed that the renal corpuscles are small dark red spherical bodies that have an average diameter of 82 μm. Podocytes contained a clear nucleus and had several large cytoplasmic primary processes, from which smaller secondary and tertiary processes emanate. The epithelium of the proximal convoluted tubule was simple cuboidal, which was covered at the apical surface by a brush border formed by sparse microvilli. Narrow intercellular spaces were observed between the cell membranes in the proximal convoluted tubule. Both descending and ascending loops of Henle were long and extended from cortex into the medulla. The distal convoluted tu- bule consisted of a simple cuboidal epithelium. These cells were covered by short microprojections at the apical surface, while at the basolateral side they had extensive plasma membrane infoldings with a few mitochondria. The juxtaglomerular (JG) and macula densa cells were present at the junction of distal tubules with afferent arterioles. The collecting ducts were lined with simple cuboidal epithelium. The cells of the medullary collecting duct had a few short apical microprojections and randomly oriented mitochondria. In this report, some histological and physiological features of individual components of nephrons in hedgehog have been discussed.

Difficult Differential Diagnoses in Testicular Pathology

Although relatively rare, testicular cancer is the most common solid organ malignancy in young men and remains a leading cause of cancer death in this population. Different types of testicular tumors are treated differently, with an overall very high cure rate with proper management. Pathologists must, therefore, be familiar with important diagnostic pitfalls in testicular pathology, particularly those that result in different treatments or prognoses. To summarize key diagnostic features and useful ancillary tools for the most frequently encountered problems in testicular tumor pathology. Current texts, PubMed (National Library of Medicine) articles, and archives at Indiana University School of Medicine and Beth Israel Deaconess Medical Center were all reviewed. Problematic differential diagnoses include seminoma versus nonseminomatous germ cell tumors, germ cell tumors versus non-germ cell tumors, intratubular germ cell neoplasia versus atypical germ cells with maturation arrest, pseudolymphovascular invasion versus real lymphovascular invasion in germ cell tumors, and macroscopic Sertoli cell nodules versus Sertoli cell tumors. In almost all cases, awareness of the differential diagnostic possibilities based on routine light microscopic features permits application of either additional, directed observations or immunohistochemical studies that lead to an accurate diagnosis.

Clinical and pathological features of a non-crystalline form of Schnyder corneal dystrophy

Schnyder corneal dystrophy (SCD) is a rare progressive bilateral disorder of the cornea resulting from an abnormal deposition of (un)esterified cholesterol and phospholipids throughout the cornea. SCD is an entity characterized by a varied spectrum of corneal changes, a fact that may cause difficulties for making the correct diagnosis. In previous publications, the clinical appearance has been described as a deposition of crystals predominantly located in the anterior stroma, accompanied by an arcus lipoides and a stromal haze [1]. However, Weiss et al. demonstrated that corneal crystals are found in only 54% of patients [2, 3], while the other patients presented with a disc-like central corneal opacity without subepithelial cholesterol crystals. Abnormal lipid deposition has been seen throughout the corneal stroma, but also in the basal epithelium, in the Bowman’s layer and occasionally within endothelial cells [2]. We present a patient with a non-crystalline form of SCD. We describe clinical aspects, and demonstrate light and electron microscopic features of this disease.

Use of Fluorescence In Situ Hybridization to Distinguish Metastatic Uveal From Cutaneous Melanoma

Metastatic lesions of malignant melanoma can on occasion be difficult to classify with regard to the primary site of origin. Given the lack of specificity of light microscopic features, ancillary studies are needed. In this study, the authors explored the possibility of distinguishing metastatic tumors derived from uveal primaries from those known to have originated from a cutaneous melanoma by fluorescence in situ hybridization (FISH) using probes for chromosome 3, 8q24, and 1p36. A total of 32 metastatic tumors were analyzed by FISH. Monosomy 3 was detected in 9 out of 16 (56.3%) cases of metastatic uveal melanoma but was not found in any of the 16 metastatic cutaneous melanomas (P < .001). With regard to 1p36, amplifications were found in 8 out of 16 (50%) cases of metastatic cutaneous melanoma but not in any case of uveal melanoma (P < .05). 1p36 was deleted in 3 cases of uveal and 1 case of cutaneous melanoma. Amplifications of 8q were found in 15 out of 16 (94%) cases of uveal melanoma metastases and in 12 out of 16 (75%) cases of cutaneous metastases. The findings suggest that FISH for monosomy 3 is a useful adjunct tool in the differential diagnosis of metastatic uveal versus cutaneous melanoma.

Pityriasis amiantacea: clinical-dermatoscopic features and microscopy of hair tufts

Pityriasis Amiantacea, also known as pseudotinea amiantacea, is a clinical syndrome which affects the scalp, having a reaction pattern reported to occur in several inflammatory dermatoses. The authors seek to establish the correlation between its clinical, dermoscopic and light microscopy features through the analysis of scale- encrusted hair tufts submitted to histological processing.

Plexiformer angiomyxoider myofibroblastischer Tumor des Magens

Recently the so-called plexiform angiomyxoid myofibroblastic tumors (PAMT) have emerged as a new entity of gastric soft tissue tumors and the light microscopic and immunohistological characteristics have now been well described. Until now PAMTs have not yet been reported in the German speaking literature. Worthy of note is that PAMTs can be diagnosed safely in sufficient biopsy material which enables adequate therapeutic steps to be initiated without delay, because PMATs although considered to be benign, can cause serious complications.

Light-microscopic characteristics of IgG4-related tubulointerstitial nephritis: distinction from non-IgG4-related tubulointerstitial nephritis

IgG4-related disease is a multi-organ disorder characterized by a high level of serum IgG4 and dense infiltration of IgG4-positive cells into affected organs. In routine studies, however, IgG subclasses are not estimated. In the present study, we attempted to clarify the light-microscopic characteristics of IgG4-related tubulointerstitial nephritis (TIN) to facilitate distinction from non-IgG4-related TIN in specimens obtained by renal biopsy using routine staining. In specimens from 34 cases of TIN (13 IgG4-related and 21 non-IgG4-related), 9 nephrologists independently reviewed the following histological features of interstitial lesions: (i) cell infiltration extending into the renal capsule, (ii) cell infiltration into the renal medulla, (iii) regional lesion distribution, (iv) lymphoid follicles, (v) granulomatous lesions, (vi) necrotizing angiitis, (vii) eosinophil infiltration, (viii) neutrophil infiltration, (ix) tubulitis, (x) peritubular capillaritis, (xi) storiform fibrosis and (xii) the stage of interstitial fibrosis. The modified nominal group technique was applied to obtain a consensus in the pathological interpretation. Consensus was successfully attained among the diagnosticians for all but one pathological feature (regional lesion distribution). Storiform fibrosis was demonstrated in 12 of 13 (92.3%) cases of IgG4-related TIN but in none of the cases of other types of TIN. Cell infiltration extending into the renal capsule was also observed only in IgG4-related TIN. Conversely, neutrophil infiltration, severe tubulitis, severe peritubular capillaritis, granulomatous lesions and necrotizing angiitis were evident only in non-IgG4-related TIN. This study revealed some useful and characteristic features for distinguishing IgG4-related from non-IgG4-related TIN on the basis of light-microscopic observation.

Morphological Studies on the Epididymal Duct of the One-Humped Camel (Camelus Dromedaries)

The present work was carried out on 20 epididymes of sexually mature one humped camel to elucidate the gross anatomical, scanning electron microscopical and light microscopical features of the epididymal duct. Anatomically, the epididymal duct of camel consists of three parts i.e. head, body and tail. Histomorphologically, the epididymal duct is subdivided into initial, middle and terminal segments, of which the middle segment is further subdivided into proximal, intermediate and distal parts. The epithelium lining the epididymal duct is ciliated pseudostratified columnar comprising mainly five cell types, namely principal, basal, apical, dark and halo cells. It displays numerous intraepithelial glands in the middle segment. In general, there is a gradual increase in the total diameter and decrease in the epithelial height of the epididymal duct from the initial to the terminal segments; that may, mechanically, facilities passage of the sperms toward the terminal segment. The lamina propria of the epididymal duct contains a layer of interlacing elastic fibers which may allow adequate elasticity of the duct that could help in its expansion. Moreover it is surrounded by numerous layers of circularly and obliquely arranged smooth muscle fibers which always increase in thickness toward the terminal segment.

Trientine and renin–angiotensin system blockade ameliorate progression of glomerular morphology in hypertensive experimental diabetic nephropathy

A comparison of the efficacy of the copper chelator, trientine, with combined renin angiotensin system (RAS) blockade on the progression of glomerular pathology in the diabetic (mREN-2)27 rat is reported. Animals were treated for 2 months with trientine, combined RAS blockers, combined trientine plus RAS blockers or none. Treatments began after inducing diabetes with streptozotocin. Physiological data were recorded monthly and light microscopic glomerular features were scored. Plasma allantoin and both plasma and renal protein carbonyls were measured as markers of oxidative stress. Trientine and RAS blockade decreased proteinuria and albuminuria and prevented an increase in creatinine clearance and kidney weight. Both reduced the diabetes-related glomerular features of mesangiolysis and glomerular segmental hypocellularity and trientine prevented severe tuft-to-capsule adhesion and reduced tubularization. Hypertension-related severe mesangial matrix expansion and global hypercellularity were increased by both treatments, which may reflect repair of mesangiolysis. Trientine reduced plasma but not renal protein carbonyls or plasma allantoin. In this model, trientine prevented the development of many diabetes-specific features similarly to RAS blockade. Amelioration of oxidative stress and features commonly observed in human diabetic nephropathy (DN), support a diabetes-related defect in copper (Cu) metabolism. The addition of Cu(II) chelation may improve current DN therapy.

Granules in Granular Cell Lesions of the Head and Neck: A Review

Granular cell lesions of the oral mucosa, jaws, and salivary glands constitute a heterogeneous group of lesions which may be either odontogenic, salivary gland, or metastatic in origin. Granular cells in these proliferations most commonly are the result of lysosomal accumulation, aging, degenerative, metabolic alteration, increased apoptosis, cytoplasmic autophagocytosis, and many more. Many benign and malignant tumors that occur in the oral cavity contain granular cells as a characteristic component of their pathology. Sometimes dilemma exists in the proper diagnosis of these granular cell lesions and the cell of origin because they share similar light and electron microscopic features. Therefore, immunohistochemistry helps to confirm histologic impressions and differentiate other neoplastic entities with granular cytoplasmic features. Granularity in a normal histopathology is a rare but innocuous change and does not influence the biologic behaviour of smooth muscle tumors except few lesions such as cutaneous granular cell angiosarcoma and granular cell ameloblastoma which have shown poor prognosis. This paper aims to review the clinical and pathologic features, different immunohistochemical profiles of granules in granular cell lesions of head and neck with an attempted working classification.

Squamous cell carcinoma with rhabdoid phenotype of skin/soft tissue in a transplant patient: An exceptional case and review of the literature

Squamous cell carcinoma with rhabdoid features (SCCRF) is a very rare and unusual cutaneous tumor. Here, we report an extraordinary case diagnosed by fine needle aspiration biopsy, in a 66-year-old man, status post multiple organ transplantation. The patient presented with a large ulcerating fungating mass in his forearm that had all the light microscopic and immunohistochemical features of a SCCRF. Previously six cases of SCCRF phenotype diagnosed by surgical pathology have been reported. This is the first case diagnosed cytologically. A review of the literature with emphasis on the differential diagnoses of such unusual rhabdoid-like tumors in fine-needle aspiration biopsy and the potential molecular mechanism for rhabdoid phenotype in transplant patients are discussed.

Microscopic evidence for inclusion of Parvamoeba Rogerson, 1993 into the order Himatismenida (Amoebozoa)

I have re-investigated the light-microscopic features of Parvamoeba rugata Rogerson, 1993, type strain CCAP 1556/1. The major characters of amoebae correspond to the initial description of this species. However, one peculiarity demonstrated by the cells during adhesion to the substratum, seems to have been partly underestimated previously. At the same time it is crucial for the explanation of this species’ position in the molecular phylogenetic trees and the recent system of Amoebozoa. This feature is the formation of a thin sheet of hyaloplasm on the ventral side of the cell that is used for adhesion to the substratum and locomotion, shared between Parvamoeba and members of the order Himatismenida. This explains the position of Parvamoeba as a sister clade to Cochliopodiidae in the molecular phylogenetic trees and justifies the recent inclusion of this genus into the order Himatismenida. In addition I sequenced the small-subunit ribosomal RNA of P. rugata and demonstrated that it was 99.5–99.7% similar to that of P. monoura Cole et al., 2010. This raises a question of the possible identity of these two species, however, several persistent morphological differences do not permit the unification of them, at least until more genes demonstrate identical sequences between these species.

Juvenile myelomonocytic leukemia characterized by cutaneous lesion containing Langerhans cell histiocytosis-like cells

We present a 1-year-old boy who developed a cutaneous lesion on the trunk and hepatosplenomegaly. Laboratory examination showed leukocytosis with peripheral blasts, atypical monocytosis, anemia, hyper IgG, and a mild elevation of C-reactive protein. Clinical features and skin biopsy findings matched the diagnostic criteria of both juvenile myelomonocytic leukemia (JMML) and Langerhans cell histiocytosis (LCH). Histopathology revealed atypical mononuclear cells that had infiltrated around vessels throughout the dermis in a skin biopsy specimen. These cells were CD1a (+), S-100 (+), CD68 (+), CD207 (-), lysozyme (+), and myeloperoxidase (-). The diagnosis of JMML was confirmed by detection of spontaneous colony formation and granulocyte-macrophage colony-stimulating factor hypersensitivity in vitro, and a somatic NRAS point mutation. Transplantation of bone marrow from an HLA-matched unrelated donor was performed, and the marrow was successfully engrafted. The cutaneous lesion and hepatosplenomegaly were improved at the time of discharge. It is often difficult to distinguish between JMML and LCH-like infiltrates by assessing clinical and light microscopic features of various cutaneous lesions. In the current case, molecular biological analysis enabled us to develop a precise diagnosis.

Pursuing an underdiagnosed disease: a simple imaging test for increasing suspicion of cardiac amyloidosis

The systemic amyloidoses are a group of uncommon diseases in which the common factor is infiltration of one or more organs with a noncellular, extracellular proteinaceous material with specific light microscopic staining characteristics [1]. Significant advances in treatment have been made over the past decade, particularly in AL amyloidosis in which the precursor protein is derived from immunoglobulin light chain fragments [2]. Transthyretin (TTR)-derived amyloidosis has also been the subject of intensive investigation, and several new therapeutic approaches have completed, or are approaching, preliminary clinical testing [3–7]. Refinements in immunohistochemical and proteomic techniques have permitted precise definition of the amyloid type, a prerequisite for initiating appropriate (and avoiding inappropriate) therapies [8]. In 2005, the Bologna group published data from 25 patients with amyloidosis (17 of whom had TTR-related amyloidosis) suggesting the bone-scanning agent Tc3,3-diphosphono-1,2-propanodicarboxylic acid (DPD) was preferentially taken up by the heart in patients with TTR amyloidosis, whereas it showed no uptake in AL amyloidosis or in controls without the disease [9]. This appeared to be isotope specific, as Tc-methylene diphosphonate (MDP) showed no uptake in 11 patients who showed distinct myocardial uptake with Tc-DPD. The authors have now expanded their original observations and, while confirming the tracer is avidly taken up in the TTR amyloid patients, they now also describe a mild to moderate uptake in one third of AL patients, thereby reducing the specificity of the test for TTR amyloidosis alone but still rendering it an interesting and informative technique [10]. Uptake of technetium-based bone imaging traces by the heart in cardiac amyloidosis is not a newly described phenomenon. As pointed out by Rapezzi and coauthors and recently reviewed in detail [11], several other nuclear imaging modalities have been proposed for imaging cardiac amyloidosis, such as Tc-aprotinin [12] and I-metaiodobenzylguanidine (MIBG) [13]. Over 25 years ago the uptake of technetium pyrophosphate (then used as a myocardial infarction imaging agent) was described in both AL and TTR amyloidosis, although the sensitivity of the imaging was subject to debate [14–16]. The type of technetium-based isotope was believed to be significant, as Tc-MDP showed little consistency for imaging amyloid cardiomyopathy, despite occasional case reports of cardiac uptake [17]. With the rapid advances in echocardiography and the echocardiographic descriptions of amyloid cardiomyopathy, technetium pyrophosphate cardiac imaging for possible amyloid cardiomyopathy became obsolete, limited to a radiologic curiosity when incidentally seen on a scan performed for other reasons such as for the evaluation of metastatic disease. Echocardiography still remains the mainstay for the initial suspicion/diagnosis of cardiac amyloidosis [1] (and was also a component of the “gold standard” used in this study), and is nowadays often complemented by cardiac MRI which R. H. Falk : S. Dorbala Cardiac Amyloidosis Program, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA

Tenofovir nephrotoxicity: acute tubular necrosis with distinctive clinical, pathological, and mitochondrial abnormalities

Tenofovir, a widely prescribed antiretroviral medication for treatment of HIV-1 infection, is infrequently associated with renal dysfunction and biopsy findings of acute tubular necrosis. We examined the clinical and pathological findings in 13 cases of tenofovir nephrotoxicity (7 men and 6 women, mean age of 51.1±9.6 years). Patients received tenofovir therapy for a mean of 19.6 months (range, 3 weeks to 8 years; median 8 months). Nine patients presented with acute kidney injury, and four had mild renal insufficiency with subnephrotic proteinuria. Mean baseline serum creatinine was 1.3±0.3 mg/dl, reaching 5.7±4.0 mg/dl at the time of biopsy, with mean proteinuria of 1.6±0.3 g/day. Glycosuria was documented in seven patients, five of whom were normoglycemic. Renal biopsy revealed toxic acute tubular necrosis, with distinctive proximal tubular eosinophilic inclusions representing giant mitochondria visible by light microscopy. Electron microscopy showed mitochondrial enlargement, depletion, and dysmorphic changes. Clinical follow-up after tenofovir discontinuation was available for 11 of 13 patients (mean duration 13.6 months). Significant recovery of renal function occurred in all patients, including four who required transient hemodialysis. Our study shows that tenofovir nephrotoxicity is a largely reversible form of toxic acute tubular necrosis targeting proximal tubules and manifesting distinctive light microscopic and ultrastructural features of mitochondrial injury.

Microvillous Inclusion Disease: A Clinicopathologic Study of 17 Cases from the UK

Background: Microvillous inclusion disease (MVID) is a rare congenital disease producing intractable secretory diarrhea in early infancy. It is characterized by diffuse intestinal villous atrophy with no inflammatory reaction. Ultrastructural identification of apical microvillous inclusions in the surface enterocytes is diagnostic. However, there is difficulty in the diagnosis of MVID due to the existence of variants (e.g., microvillous dystrophy), possible disease resolution, and tissue orientation for electron microscopy (EM). The authors analyzed materials from 4 patients with MVID from a single institution. The morphologic features, distribution of lesions, biomarkers, and complementary ultrastructural characteristics were studied. Design: Materials of MVID cases were collected from 6 different hospitals in the United Kingdom between 1990 and 2008. Epidemiological data, including age range, median, mode, sex ratios, and follow-up, were retrieved. All intestinal biopsy specimens were analyzed histologically, histochemically (for PAS, n = 17), immunohistochemically (for CD10, n = 2 and polyclonal CEA, n = 4), and ultrastructurally (n = 9). Results: Ultrastructurally, apical microvillous inclusions in surface enterocytes in duodenal biopsies were identified in all cases, while 1 case had variant morphology (microvillous dystrophy and very occasionally atypical microvillous inclusions). Tissue orientation for EM was supportive for identification of inclusions in apical enterocytes. Morphologically, a bubbly vacuolated appearance of the apical cytoplasm with extensive or patchy absence of the brush border with occasional cytoplasm inclusions was observed in the enterocytes. Some of these changes vaguely resembled gastric mucin cell metaplasia. Architecturally, villous blunting with either crypt hypoplasia or hyperplasia and absence of inflammation were common findings. The epithelial changes were also found in colon biopsies. PAS, CD10, and p-CEA showed a bright apical cytoplasmic blush/staining, which correlated ultrastructurally with apical granules with inclusions of variable electron density in all cases. These stains also highlighted the targetoid inclusions. Conclusion: Besides electron microscopy identification of inclusions, the light microscopic morphological features together with the biomarker studies highlighting the apical cytoplasmic blush are quite unique and diagnostic of MVID. Furthermore, it is the opinion of the authors that a diagnosis of MVID can be made without electron microscopy.

Molecular pathology of chromophobe renal cell carcinoma: A review

The recognition of chromophobe renal cell carcinoma (RCC) among other distinct types of renal cell tumors (RCT) based on light-microscopic features, such as cytoplasmic and nuclear characteristics, might pose a dilemma in some cases because of morphological pattern overlapping with renal oncocytoma or conventional RCC. The present article reviews chromophobe RCC with focus on aspects of its molecular pathology, which was shown using ancillary modern microarray-based technology that can distinguish it from its mimics and therefore be helpful for its correct diagnosis. Although the high resolution DNA-microarray analyses excluded with all certainty the occurrence of small specific alterations, the loss of entire chromosomes 2, 10, 13, 17 and 21 occurs exclusively in chromophobe RCC and therefore probes localized at these chromosomes might be used to establish the diagnosis of chromophobe RCC in cases with uncertain histology. The usefulness of proposed candidate genes selected by the global gene expression analyses in the diagnostic pathology is far below expectations. The conflicting staining patterns, together with the poor specificity of used antibodies, leads us to believe that these candidate immunomarkers might not help in the separation of chromophobe RCC, with the exception of CD82, which has recently been suggested to be used for routine histological diagnosis.

Electron microscopic findings in non‐alcoholic fatty liver disease: Is there a difference between hepatosteatosis and steatohepatitis?

Non-alcoholic fatty liver disease has long been accepted as benign; however, recent evidence suggests that the disease may progress to cirrhosis and hepatocellular carcinoma, although the natural course of the disease is still unclear. This study was designed to comparatively evaluate electron microscopic features of non-alcoholic fatty liver (NAFL) and non-alcoholic steatohepatitis (NASH). Quantitative and semi-quantitative ultrastructural evaluations were performed on liver biopsies from 23 patients, 10 with NAFL and 13 with NASH. No statistically significant difference was noted between NAFL and NASH patients in ultrastructural features of hepatocytes including megamitochondria, intramitochondrial crystalline inclusions, mitochondrial matrix granules, foamy cytoplasmic appearance, electron-lucent and glycogen-containing nuclear regions, lipofuscin granules, or an increased frequency of vesicles containing electron-dense material in peribiliary Golgi zone; however, the mitochondrial diameter was significantly higher in the NASH patients. Intercellular distance and microvilli between hepatocytes, collagen and electron-dense material accumulation in the space of Disse, electron-dense material accumulation and microvillus density in bile canaliculi did not differ significantly between the groups. Our data show that, although NAFL and NASH can be distinguished by their distinct light microscopic features, ultrastructural characteristics are similar, which suggests that NAFL may also have the potential to progress to fibrosis and cirrhosis like NASH.

Light Microscopic Features of Membranous Nephropathy With Unusual Changes of the Podocytes and Glomerular Basement Membrane in a Patient With Sudden Onset of Nephrotic Syndrome

Membranous nephropathy (MN) is a pathologic entity characterized by a spectrum of changes in the glomerular basement membrane (GBM). Diagnostic features include subepithelial immune deposits and thickening of the GBM.1 In 1968, Ehrenreich and Churg2 proposed a morphologic classification of MN using electron microscopic findings. This classification was based on immune deposits in the GBM, GBM reaction to the deposits, and resolution of glomerular injury with resorption of the deposits. However, some biopsy specimens with features of MN also show spherical microparticles and podocyte microvillous entrapment in thickened GBM on electron microscopy.

Sarcocystis calchasi sp. nov. of the domestic pigeon (Columba livia f. domestica) and the Northern goshawk (Accipiter gentilis): light and electron microscopical characteristics

A novel highly pathogenic Sarcocystis species has been shown to cycle between the Northern goshawk (Accipiter gentilis) as definitive host and the domestic pigeon (Columba livia f. domestica) as intermediate host. However, genetically based characteristics are only available from very few bird-infecting Sarcocystis species. We therefore further characterised morphological properties of this protozoan in both hosts. Using light and electron microscopy, oocysts and sporocysts as well as schizonts and sarcocysts were characterised and compared with available morphological features of previously reported Sarcocystis species of Northern goshawks, Columbidae and genetically closely related species of other avian hosts. Sporocysts shed from day 6 on after experimental infection by the Northern goshawk were of ovoid appearance (11.9 x 7.9 microm). Ultrastructurally, schizonts of all developmental stages were found in the liver, spleen and next to or in endothelial cells of various organs of domestic pigeons 7 to 12 days after experimental infection. The cyst wall surface of slender sarcocysts (1 to 2 mm in length and 20 to 50 microm in width) was smooth and lacked protrusions. Cystozoites were lancet-shaped and measured 7.5 x 1.5 microm in Giemsa stain smears. The morphological findings, when combined with data of experimental infection and genetic studies, convergently indicate that the recently discovered Sarcocystis species represents a new species. We therefore propose to name this parasite Sarcocystis calchasi species nova.