Neurosecretory cells of the lamina propria of the appendix and their possible relationship to carcinoids

Appendiceal Well-Differentiated Neuroendocrine Tumors: A Single-Center Experience and New Insights into the Effective Use of Immunohistochemistry

Background. Appendiceal well-differentiated neuroendocrine tumor is the most common histological type of appendiceal tumor. The majority of tumors are found incidentally at the tip of the appendix, with few exceptions. Due to its primarily indolent nature, this entity presents unique pathological challenges, particularly in the appropriate use of immunohistochemistry which this study aims to clarify. Patients and methods. Patients diagnosed at University Health Network (Canada) between 2005–2019 were selected and reviewed. Results. We identified 70 patients and sex distribution was female 60%; median age 36.5 years. Among them, 63 patients underwent appendectomy, and seven had initial right hemicolectomy for non-appendix lesions. Mean tumor size was 5.0 mm. Tumor extent was submucosa (15%); muscularis propria (34%); subserosa or mesoappendix (42%); visceral peritoneum (8%). All were clinically non-functional and negative for nodal and distant metastasis. Ninety percent of tumors were WHO Grade 1; 10% were WHO Grade 2. Immunohistochemically, an average of six stains were performed per patient. Nearly all tumors were positive for chromogranin A, synaptophysin, CAM5.2, and CDX2. MIB-1 staining was < 3% in 58/63 tumors. Other immunohistochemical stainings performed were hormonal markers (serotonin, glucagon, pancreatic peptide, peptide YY). Subsequent right hemicolectomy was performed on five patients. All were followed up (median 4 years 8 months), and all were alive without recurrence except for one patient who died of another comorbidity. Conclusion. Tumors that are small, localized, and of low grade can be reasonably exempt from an extensive immunohistochemical panel in the absence of non-typical clinical and morphological features.

The origin of neuroendocrine tumors and the neural crest saga

In this essay, the role of the neural crest in the development of the vertebrate embryo is briefly described. The techniques used to document the neural crest origin of various cell types and the tumors arising from them are discussed, with emphasis on Le Douarin's quail-chick chimera model. The current dogma on the origin of the cells of the diffuse endocrine system is presented, and some personal conjectures based on the microscopic appearances of various types of normal, vestigial and neoplastic human tissues are offered to the reader as 'food for thought.'

Pathologic classification and clinical behavior of the spectrum of goblet cell carcinoid tumors of the appendix

Appendiceal tumors exhibiting both neuroendocrine and glandular differentiation are uncommon and have caused difficulty in pathologic classification, prediction of prognosis, and clinical management. Previously, such lesions have been variously designated as adenocarcinoid, goblet cell carcinoid (GCC), and mixed adenocarcinoma carcinoid. In this study, we undertook a retrospective investigation of 63 such cases and classified them as typical GCC (group A) and adenocarcinoma ex GCC on the basis of the histologic features of the tumor at the primary site. The adenocarcinoma ex GCC group was further divided into signet ring cell type (group B) and poorly differentiated adenocarcinoma type (group C). The clinical characteristics and prognosis were compared within these groups and with conventional de novo appendiceal adenocarcinomas. Both groups A and B tumors shared a similar immunoprofile, which included generally focal immunoreactivity for neuroendocrine markers, and a normal intestinal type mucin glycoprotein profile (negative MUC1 expression and preserved MUC2 immunoreactivity). The proliferative index was relatively low in these tumors and slightly increased from groups A to B tumors (11% to 16%). Both beta-catenin and E-cadherin exhibited a normal membranous staining pattern in groups A and B tumors. The poorly differentiated adenocarcinomas ex GCC (group C) demonstrated abnormal p53 and beta-catenin immunoreactivity. The mean follow-up time was 49+/-5 (SE) months. The overall disease-specific survival for all subtypes was 77%, with 46% of patients without evidence of disease and 31% alive with disease. The mean survival was 43+/-7 months. All the patients with clinical stage of I or IIA disease had a favorable outcome after appropriate surgery with or without chemotherapy. Although most patients (63%) with GCC presented at an advanced clinical stage, their clinical outcome could be differentiated by subclassification of tumors. The stage IV-matched 5-year survival was 100%, 38%, and 0% for groups A, B, and C, respectively. In conclusion, GCC is a distinctive appendiceal neoplasm that exhibits unique pathologic features and clinical behavior. They display a spectrum of histologic features and possess the potential to transform to an adenocarcinoma phenotype of either signet ring cell or poorly differentiated adenocarcinoma types. Careful evaluation of the morphologic features of GCCs and appropriate pathologic classification are crucial for clinical management and prediction of outcome. Surgical management with right hemicolectomy is recommended after appendectomy for most cases, particularly those with an adenocarcinoma component (groups B and C).

Neuroendocrine tumors of the appendix

The vast majority of neuroendocrine neoplasms of the appendix are carcinoid tumors. Most are of enterochromaffin (EC) cell type, although rare examples are of L cell type. EC cell carcinoids of the appendix differ from those encountered elsewhere in the gastrointestinal system. For example, they are remarkably common given the small size of the appendix, are usually benign, occur in younger patients, and typically contain sustentacular cells that express S-100. Origin from subepithelial neuroendocrine cells could explain these characteristics. It has also been suggested that most appendiceal carcinoids are hyperplastic rather than neoplastic, although this hypothesis requires further study. Nevertheless, truly neoplastic EC cell carcinoids of the appendix undoubtedly occur, and those greater than 2 cm in diameter have a significant risk of producing distant metastases. Carcinoid syndrome is a very rare presentation. Tubular carcinoids are unusual benign neoplasms; it has been proposed that they represent L cell carcinoids with a predominant tubular pattern of growth. Goblet cell carcinoids tend not to produce a grossly visible tumor mass but diffusely infiltrate the wall. They typically exhibit tight clusters of goblet cells, usually with scattered neuroendocrine cells and sometimes with Paneth cells, sometimes surrounding a small lumen. They may behave as a low-grade malignancy. The distinction between goblet cell carcinoid and other types of tumor is of great importance because of the implications for treatment and prognosis. Frank adenocarcinoma can arise from goblet cell carcinoids, and tumors with both components are classified as mixed goblet cell carcinoid-adenocarcinoma. The carcinoma component of the latter determines their prognosis, which would be worse than for a goblet cell carcinoid alone.

Sustentacular cells in pulmonary neuroendocrine tumours

AIMS

To determine the prevalence of sustentacular cells across the range of pulmonary neuroendocrine tumours: typical and atypical carcinoid tumours and large cell and small cell neuroendocrine carcinomas.

METHODS AND RESULTS

Sustentacular cells were sought in 80 pulmonary neuroendocrine tumours by immunolabelling for S100 protein, nerve growth factor receptor and glial fibrillary acidic protein. Intratumoural macrophages and Langerhans cells were identified with the KP 1 (CD68) and CD1A antibodies. S100-positive sustentacular cells were present in 25 of 30 typical carcinoids, 200 of 25 atypical tumours, six of 10 large cell carcinomas and six of 15 small cell lesions. They were most numerous in the typical carcinoids but very few in the small cell carcinomas, their prevalance being clearly related to grade of differentiation and, in particular, to the degree of architectural organization.

CONCLUSIONS

Sustentacular cells are often found in pulmonary neuroendocrine tumours, especially better-differentiated lesions with a well-developed architecture. their prevalence clearly reflecting the degree of structural organization. Whether their prevalence is a useful prognostic indicator within a particular group of such tumours, such as the atypical carcinoids or the large cell carcinomas, as appears to be the case with paragangliomas, is unclear.

A retrospective analysis of 1570 appendiceal carcinoids

OBJECTIVE

Information about the management and outcome of appendiceal carcinoids is sparse, because few series comprise more than 100 cases. In this study we have analyzed the epidemiology of 1570 appendiceal carcinoids, to compare outcome with other gastrointestinal carcinoid tumors.

METHODS

We evaluated 1570 appendiceal carcinoids in a series of 8305 carcinoid tumors from the SEER, the End Results Group, and the Third National Cancer Survey programs of the National Cancer Institute over the time period 1950-1991.

RESULTS

Appendiceal carcinoids comprised 18.9% of all carcinoid tumors and exhibited a marked female predominance (M/F ratio: 0.47). Age-adjusted incidence rates were 1.7-fold higher in women compared to men. Appendiceal carcinoids present earlier (average age: 42.2 yr) than other gastrointestinal carcinoids (62.9 yr) or noncarcinoid appendiceal tumors (61.9 yr). At the time of diagnosis 35.4% were nonlocalized. The overall 5-yr survival for localized lesions was 94%, for regional invasion 84.6%, and for distant metastases 33.7%. The 5-yr survival of appendiceal carcinoids (85.9%) was the highest among all types of carcinoid tumors. In 14.6% noncarcinoid tumors at other sites were also evident.

CONCLUSION

The high relative incidence of carcinoid tumors in the appendix is still poorly understood. The good overall 5-yr survival rates of appendiceal carcinoids as opposed to other carcinoids represents either a different biological behavior, earlier diagnosis, or expeditious management (appendectomy). However, the increased likelihood of coexisting neoplasms and the not uncommon presentation of metastatic disease should warrant careful evaluation and postoperative follow-up of such lesions.

Dual carcinoid/epithelial neoplasia of the appendix

We report a series of 13 lesions of the human vermiform appendix in which a carcinoid component was associated with a separate non-carcinoid epithelial component that included an adenoma-like lesion of the mucosal epithelium. We use the term dual carcinoid/epithelial neoplasia to describe this phenomenon. The carcinoid component was insular/trabecular in nine cases, tubular in one case and of goblet cell type in three. The epithelial component was a mucinous cystadenoma in four, a mucinous tumour of uncertain malignant potential in three, and a mucinous cystadenocarcinoma in six. No intermediate cell population was seen and in three cases the carcinoid and epithelial components were in different parts of the appendix, leading us to suggest that these lesions may be true 'collision' tumours in which two neoplasms have arisen in the same organ. The prognosis appears to be no worse than for either of the components alone, but conclusions regarding these lesions must be guarded on account of their rarity and the small numbers available for study.

Endocrine tumors of the small and large intestine

Among endocrine tumors arising in the intestinal tract, midgut argentaffin EC cell carcinoids, duodenal gastrin cell tumors and rectal trabecular L cell carcinoids, in order of decreasing frequency, are those better represented. Together they account for more than 80% of such tumors. Duodenal somatostatin cell tumors, gangliocytic paragangliomas and poorly differentiated neuroendocrine carcinomas, are also well defined tumor entities. The carcinoid syndrome with intermittent flushing, hypotension and diarrhea, and the Zollinger-Ellison syndrome with severe peptic ulcer disease, are the only hyperfunctional syndromes consistently found in association with these tumors. The carcinoid syndrome arises in about 10% of intestinal carcinoids, usually in their advanced metastatic stage. The Zollinger-Ellison syndrome occurs in association with about 40% of gastrin cell tumors, including small intramural growths. Tumor prognosis depends on mode and site of presentation, histology, cell type(s), size, level of invasion, metastases (especially distant metastases) and associated clinical syndrome or background disease.

Cytokeratin expression in small intestinal and appendiceal carcinoids. A basis for classification

For a study of histogenesis of intestinal carcinoids a collection of 5 classical small intestinal carcinoids, 6 appendiceal carcinoids and 9 pheochromocytomas, were evaluated. The tumors were identified by routine morphology, silver staining and chromogranin immunocytochemistry and were then examined with regard to the expression of intermediate filaments of cytokeratin type. Eight different antisera identifying individual or combinations of cytokeratins were employed. All classical small intestinal carcinoids displayed cytokeratin immunoreactivity and an almost identical cytokeratin reaction was observed in the normal enterocytes of the small intestinal mucosa. Of the individual cytokeratin types, number 18 was most heavily expressed. The appendiceal carcinoids, like the pheochromocytomas, almost totally lacked a cytokeratin staining despite a positive reaction in the mucosa of the appendix. This, in agreement with some previous studies, indicates that the small intestinal carcinoids are histogenetically related to the epithelial cells of the intestinal mucosa, while the appendiceal carcinoids have a different histogenesis and are more like pheochromocytomas. The appendiceal carcinoid may represent a distinct type of intestinal paraganglioma. This offers one explanation for the different biological behavior of appendiceal carcinoids in comparison with the other intestinal carcinoids.

Intestinal carcinoid tumor and myotonic dystrophy. A new association?

The occurrence of multiple carcinoid tumors of the small bowel with liver metastases is reported in a patient with a previous myotonic dystrophy. In addition to the association of myotonic dystrophy with multiple endocrine adenomatosis type 2A, hyperparathyroidism, and neurofibromatosis, this case report gives further evidence for the propensity of such patients to develop neuroendocrine tumors.

A comparative immunohistochemical study of jejunoileal and appendiceal carcinoids. Implications for histogenesis and pathogenesis

BACKGROUND

The purpose of this study was to determine the histogenesis of jejunoileal and appendiceal carcinoids and to ascertain whether this could be useful in further explaining the pathology of these neoplasms.

METHODS

Eight cases each of multiple jejunoileal carcinoids and appendiceal carcinoids together with their respective age-matched and sex-matched controls were stained with silver stains, chromogranin A, serotonin, and S-100. Histomorphometric evaluations of the endocrine cells in the mucosa adjacent to the carcinoids were carried out and compared with the respective controls using the Student's t test.

RESULTS

All the carcinoids from both groups stained for argyrophilia, argentaffinity, chromogranin A, and serotonin. Histomorphometric evaluations showed intraepithelial endocrine cell hyperplasia (IECH) in the jejunoileal carcinoid group (P = 0.007, chromogranin; P = 0.004, serotonin) but not in the appendiceal carcinoid group. On the other hand, subepithelial endocrine cell aggregates that were separate from the main tumor were seen in two cases of appendiceal carcinoids. With S-100, all appendiceal carcinoids showed intrinsic tumor positivity whereas the jejunoileal carcinoids did not.

CONCLUSIONS

The finding of IECH with multiple jejunoileal carcinoids suggests that these carcinoids arise from a field effect. The absence of IECH with appendiceal carcinoids as well as their association with subepithelial endocrine cell aggregates and their intimate relationship with Schwann cell processes suggests that appendiceal carcinoids arise from a more discrete unit, the subepithelial neuroendocrine complex.

Age, site and distribution of subepithelial neurosecretory cells in the appendix

The appearance of subepithelial neurosecretory cells (SNC) was investigated by studying completely sampled appendices of 50 children, adolescents and adults. The cells were demonstrated using lead hematoxylin, a selective stain for neurosecretory cells. Additional routinely sampled specimens were also studied for comparison. In children up to the age of 9 yrs only occasional SNC were found. After this age, however, SNC were present in most appendices and in greater numbers. The majority of SNC were located in the distal portion of the appendix, with only small numbers of these cells being present in the proximal segment. Occasional SNC-like cells were identified in the appendiceal submucosa in all regions of the appendix at all ages. This lends support to the hypothesis that a correlation exists between the presence of increased numbers of SNC, patient age and the site distribution of both acute appendicitis and appendiceal carcinoid tumors.

The histogenesis of appendiceal carcinoid tumours

Twenty-two appendiceal carcinoid tumours, comprising 10 classical carcinoids, six tubular carcinoids and six goblet cell carcinoids were examined by histochemistry and immunohistochemistry. All of the tumours showed evidence of neuroendocrine differentiation. Classical carcinoids were invariably intimately associated with S-100 protein positive cells, supporting an origin from sub-epithelial neuroendocrine cells. Both tubular and goblet cell carcinoids expressed cytoplasmic mucin and immunoglobulin A, and neither were associated with S-100 protein positive cells. These observations suggest that tubular and goblet cell carcinoids are derived from epithelial crypt stem cells.

The topographical and age distributions of neuroendocrine cells in the normal human appendix

In order to clarify the histogenesis of appendiceal carcinoid tumours, epithelial (ENC) and subepithelial (SNC) neuroendocrine cells were counted at four sites in 50 normal appendices stained by standard argyrophil and argentaffin techniques. In general, ENC were present in similar number at all sites within the appendix, whereas SNC were more numerous at the tip than at the base. The number of ENC was similar throughout life, apart from an increase in one neonate and some elderly patients, whereas SNC were maximal in young adults. Thus, the topographical and age distributions of SNC, but not those of ENC, parallels the topographical and age incidence of appendiceal carcinoid tumours, suggesting that most appendiceal carcinoid tumours arise from SNC rather than ENC.

Histopathology, hormone products, and clinicopathological profile of endocrine tumors of the upper small intestine: A study of 44 cases

Forty-two duodenal and 3 upper jejunum tumors from 44 patients were investigated. All tumors were tested immunohistochemically for gastroenteropancreatic hormones and general endocrine cell markers. Twenty-eight of the 45 tumors (62%) proved to be gastrin cell tumors, with (12 cases) or without (16 cases) associated Zollinger-Ellison syndrome. Zollinger-Ellison syndrome was part of type 1 multiple endocrine neoplasia syndrome in 3 cases. Twenty-three of the 28 gastrin cell tumors (82%) were from proximal duodenum, 2 were from the second part of the duodenum, and 3 were from the upper jejunum. Seven cases were somatostatin cell tumors, 6 of which were from the ampullary region; 5 cases were associated with biliary tract disease and 2 with associated cutaneous neurofibromatosis. Four ganglioneuromatous paragangliomas, from the ampullary region or nearby duodenum, showed somatostatin cells, coupled with pancreatic polypeptide cells in 2 cases. Two serotonin-producing argentaffin carcinoids were also identified. In addition to the main cell type, 30 tumors showed one or more, usually minor, cell populations producing somatostatin, serotonin, cholecystokinin, pancreatic polypeptide, insulin, neurotensin, or the alpha chain of human chorionic gonadotropin. Only 3 tumors lacked hormone immunoreactivity. Some correlation has been noted between histological structure and hormone content of tumor cells, with prevalence of broad gyriform trabeculae and vascular pseudorosettes among gastrin cell tumors, tubuloacinar patterns among somatostatin cell tumors, thin parallel trabeculae among PP cell growths, and a solid nest pattern among argentaffin carcinoids. Deep infiltration of the intestinal wall was observed in 22 tumors, 6 of which also had metastases to local lymph nodes. All metastatic cases were among ZES tumors or ampullary somatostatin cell tumors. Ganglioneuromatous paragangliomas and nonfunctioning gastrin cell tumors had essentially benign behavior, even when involving deep strata of the intestinal wall. Post operative follow-up study of 36 cases, including all metastatic tumors, showed no evidence of tumor-related death or progressive tumor disease.

Epithelial changes following bone marrow transplantation: cytological atypia and epithelial endocrine cells

This report describes the histological and immunocytochemical findings in gastrointestinal biopsies and skin of a patient with chronic granulocytic leukaemia which progressed to blastic transformation, who was then treated with chemotherapy and total body irradiation followed by allogeneic bone marrow transplantation. The gut showed endocrine cells in the lamina propria and these had an immunophenotype similar to the glandular epithelium at the sites studied (stomach, duodenum and rectum), supporting the idea that the endocrine cells of the gut are more resistant to the effect of radiation, chemotherapy and graft-versus-host disease (GVHD) than are other cell types in the epithelium, and that lamina proprial endocrine cells are epithelially derived in this situation. Epidermis and gut epithelium also showed marked atypia due to the conditioning regimen and GVHD, and this case illustrates the possibility of misdiagnosis of carcinoma in this increasingly common situation. An additional, unusual feature of this case was the presence of a B-cell UCHL1 + ve lymphoma of the colon at autopsy, 122 days post-transplantation.

Laryngeal paragangliomas and neuroendocrine carcinomas

Forty-eight neuroendocrine tumours of the larynx were studied, of which 41 were classified as large cell neuroendocrine carcinoma. Most of these tumours occurred in the supraglottic larynx and the patients were predominantly male. Exquisite pain was a presenting feature in one third. These carcinomas metastasized, frequently to skin, giving rise to painful secondary lesions, but long-time survival occurred. Histologically, large cell neuroendocrine carcinoma had a number of features seen in neuroendocrine tumours at other sites, including grouping into 'Zellballen' which mimics paraganglioma. Four tumours were definite paragangliomas. These tumours have behaved benignly. There were three cases of small cell neuroendocrine carcinoma, a tumour which is histologically identical to its counterpart in the bronchus and has a very aggressive course. All three types of tumour expressed general neuroendocrine markers, but only large cell neuroendocrine carcinoma marked for both cytokeratin and calcitonin. In the paraganglioma cases sustentacular cells were identified and marked for S-100 protein and glial fibrillary acidic protein. Histological examination, supplemented with immunohistochemistry, helped distinguish these tumours into those requiring different treatment regimens.

The innervation and neuroendocrine cell population of the appendix in total colonic aganglionosis

There is little published information on changes in the appendix in Hirschsprung's disease despite the presence within the mucosa of nerves and neuroendocrine cells together forming a 'neuroendocrine ganglion'. The innervation and neuroendocrine cell population of 11 appendices (two from patients with total colonic aganglionosis, six from patients with short segment Hirschsprung's disease and three normal controls) were examined using H & E, a standard Grimelius silver stain and immunocytochemistry for S-100 protein, neuron-specific enolase, neurofilament and synaptophysin. Compared with both normal and short segment Hirschsprung's disease controls, the total colonic aganglionosis appendices showed decreased numbers of nerve bundles around the muscle layers and within the submucosa, markedly decreased numbers of smaller fibres within the circular muscle and absence of the finer fibres within the lamina propria. There was no change in the overall number of epithelial neuroendocrine cells but subepithelial neuroendocrine cells, normally found in association with mucosal nerve fibres, were totally absent. The concomitant loss of nerve fibres and neuroendocrine cells from the lamina propria in total colonic aganglionosis suggests a different embryological origin for epithelial and sub-epithelial neuroendocrine cells.

Neuronal hyperplasia in the anal canal

In a consecutive series of minor surgical specimens from the anal canal, neuronal hyperplasia was found in nine of 56 haemorrhoidectomy specimens and in four of 23 fibrous polyps. In an additional series of 14 resections of the anal canal, neuronal hyperplasia was present in six cases, of which five showed haemorrhoids. In all cases, neuronal hyperplasia was located in the submucosa beneath squamous epithelium and extended over an area from 5 to 12 mm. Immunohistochemically, the foci of hyperplasia were found to consist of both neuronal and Schwann cell components. Staining for vasoactive intestinal peptide, neuropeptide Y and calcitonin gene related peptide, did not demonstrate any increased terminal density. It is suggested that anal neuronal hyperplasia in these cases represents an acquired lesion due to local mechanical influence.

Bronchial carcinoids with S-100 positive sustentacular cells. A comparative study with gastrointestinal carcinoids, pheochromocytomas and paragangliomas

Fourty-six bronchial carcinoids, twelve tumourlets and twenty areas of neuroendocrine cell dysplasia (NED) were immunohistochemically evaluated for various neuroendocrine markers, S-100 protein (S-100), myelin basic protein, intermediate filaments, actin, Leu-7 and several neurohormonal polypeptides. Eighteen of the bronchial carcinoids (39.1%) showed a biphasic cell pattern, with abundant stellate-shaped S-100 positive cells (SC). SC were not reactive for chromogranin A, myelin basic protein, cytokeratins, neurofilaments, glial fibrillary acidic protein or actin, and were only occasionally weakly positive for vimentin. SC were not detected in the tumourlets nor in the NED observed. For comparison a group of other neuroendocrine tumours (11 gastrointestinal carcinoids, 4 pheochromocytomas and 4 paragangliomas) were immunostained for S-100, chromogranin A and actin. SC similar to the ones detected in the bronchial carcinoids could be detected in appendiceal carcinoids, paragangliomas and in two out of four pheochromocytomas. Our present data are in keeping with a Schwannian/sustentacular nature of SC rather than that of a histiocytic or myoepithelial nature. We suggest that SC-rich bronchial carcinoids are biphasic tumours, which could be designed "paraganglioid" bronchial carcinoids. The relationship between SC-rich bronchial carcinoids and tumourlets/NED is a matter of further investigation: SC-rich bronchial carcinoids may either differentiate in a biphasic pattern during tumoural growth or may not be histogenetically related to tumourlets.

Mast cells are closely apposed to nerves in the human gastrointestinal mucosa

Mast cell/nerve associations have been recorded in several publications; however, the human gastrointestinal tract has received little attention. Accordingly, mucosal samples from small bowel, appendix, and large bowel were studied. Combined histochemical/immunocytochemical techniques revealed that the proportion of mast cells apposed to nerves ranged from 47.08% +/- 6.10% to 77.66% +/- 4.26%. The highest incidence of contact was observed in the appendix; where the apparent nerve density was also greater than in the large or small bowel. Electron-microscopic studies revealed many mast cells adjacent to nerve fibers and membrane-to-membrane contact between axonlike processes and mast cells. Often, these processes were dilated, as were axons in adjacent nerve fibers. These data provide a microanatomic basis for potential communication between nerves and mast cells in the human gastrointestinal mucosa. This may be of physiologic significance in the normal individual and important in disease processes, such as inflammation and fibrosis.

Gastrointestinal carcinoid tumours. Histogenetic, histochemical, immunohistochemical, clinical and therapeutic aspects

The increased knowledge of the pathobiology of gastrointestinal carcinoid (neuroendocrine) tumours and the improved therapeutic possibilities have brought a demand for more precise diagnosis. Although the carcinoid tumours can often be tentatively recognized in routinely processed microscopic slides, their more accurate identification requires additional diagnostic procedures. General neuroendocrine markers such as the argyrophil reaction of Grimelius and immunohistochemistry with application of antibodies against chromogranin A and of neuron-specific enolase are discriminatory staining methods which are used to reveal the neuroendocrine origin of almost all highly differentiated carcinoid tumours of the gastrointestinal tract. Mid-gut carcinoids, which predominate among these tumours almost unexceptionally contain serotonin. This biogenic amine can be demonstrated by the argentaffin reaction of Masson, serotonin immunoreactively or by formalin-induced fluorescence. The characteristic staining pattern of mid-gut carcinoids is almost invariably preserved in the metastatic deposits and consequently the staining methods for identifying serotonin can also be used on metastases to reveal a primary mid-gut carcinoid. The enterochromaffin-like (ECL) cell carcinoids of the body and fundic area of the stomach often seen in association with pernicious anaemia are argyrophil with the Sevier-Munger silver stain. Other neuroendocrine tumours, viz. antral, duodenal and rectal carcinoids should be studied by a battery of relevant peptide hormone antisera for adequate diagnosis. During the last decade new peptide hormones have been found in circulation in patients with carcinoid tumours, but serotonin and urinary 5-HIAA are still the most important markers for carcinoids of the mid-gut origin. Other clinically useful tumour markers are chromogranin A + B, pancreatic polypeptide, human chorionic gonadotropin alpha and beta subunits. For localizing procedures, angiography is the most reliable investigative method for primary tumours in the gut, whereas CT-scan and ultrasound investigations are good for detection of liver metastases. During the last five years, the therapy for malignant carcinoid tumours has been considerably improved. Chemotherapy has only revealed objective response rates in about 10-30% of the patients giving median survivals from start of therapy of about 10 months. Recently treatment with alpha interferons and the new somatostatin analogue octreotide have given objective responses in 50-75% of patients with malignant mid-gut carcinoid tumours. These patients have now a median survival from start of therapy of 70 months when treated with alpha interferons. In the future new therapies will come into use such as monoclonal antibodies and perhaps also agents blocking different growth factors.

Neuroendocrine cell proliferations in gastric antral vascular ectasia

Gastric antral vascular ectasia is a recently recognized cause of chronic gastrointestinal blood loss. Immunohistochemical and electron-microscopic studies were performed on the surgically resected antrum of a patient with antral vascular ectasia. These revealed extraepithelial and intraepithelial neuroendocrine cell proliferations. Staining for a wide range of neural and endocrine markers demonstrated that these cells contain large quantities of 5-hydroxytryptamine and vasoactive intestinal polypeptide. Gastric vascular ectasia is of unknown etiology but has been associated with achlorhydria and liver cirrhosis. The findings suggest that locally released neurotransmitters may be responsible for local vasodilation and hence a propensity to bleed.

Adenocarcinoid tumor of the periampullary region: a novel duodenal neoplasm presenting as biliary tract obstruction

An adenocarcinoid tumor of the duodenum, similar to those arising in the appendix, is reported. The tumor presented as a periampullary mass causing pancreaticobiliary obstruction. The microscopic features were typical of adenocarcinoid with diffuse infiltration of mucosa, submucosa, and smooth muscle by tubuloglandular structures lined by enteroendocrine and goblet cells. Signet ring cells were also present. It is desirable to distinguish adenocarcinoids from adenocarcinomas and typical carcinoids in this setting as, by analogy with appendiceal tumors, adenocarcinoids may be expected to have an intermediate prognosis.

Histogenesis of a duodenal carcinoid

A duodenal carcinoid with a diameter of 9 mm was cut serially into 5 microns thin sections from one end to the other. Every fourth section was stained with the argyrophil method of Grimelius, while representative sections in between were used for immunohistochemical analyses. The tumor displayed an argyrophil reaction and was chromogranin A immunoreactive and S-100 protein negative. Furthermore, the majority cell population was gastrin-immunoreactive, while minor cell populations stained for somatostatin and serotonin. The serial sectioning revealed that the tumor arose from differentiated endocrine cells located in the mucosal crypts. In the duodenal mucosa in the vicinity of the tumor the epithelial crypts exhibited an increased number of endocrine cells, preferentially displaying gastrin immunoreactivity. The results indicate that in this particular case the carcinoid tumor arose from hyperplastic and differentiated endocrine cells in the epithelial crypts of the duodenal mucosa.

Diagnostic pathology of gastrointestinal and pancreatic neuroendocrine tumours

The increased knowledge of the pathobiology of gastrointestinal and pancreatic neuroendocrine tumours and the improved therapeutic possibilities have brought a demand for more precise diagnosis. Although the neuroendocrine tumours can often be tentatively recognized in routinely processed microscopic slides, their more accurate identification requires additional diagnostic procedures. General neuroendocrine markers, such as the argyrophil reaction of Grimelius and immunohistochemistry with application of antibodies against chromogranin A and of neuron-specific enolase are discriminatory staining methods which are used to reveal the neuroendocrine origin of almost all highly differentiated neuroendocrine tumours of the gastrointestinal tract (carcinoids) and pancreas (insulomas). Midgut carcinoids, which predominate among these tumours almost unexceptionally contain serotonin. This biogenic amine can be demonstrated by the argentaffin reaction of Masson, serotonin immunoreactivity or by formalin-induced fluorescence. The characteristic staining pattern of midgut carcinoids is almost invariably preserved in the metastases and can thus be used to reveal a primary midgut carcinoid. The enterochromaffin-like (ECL) cell carcinoids of the body and fundic area of the stomach are argyrophil with Sevier-Munger silver stain. Other neuroendocrine tumours, viz, antral, duodenal and rectal carcinoids and insulomas, should be studied by a battery of relevant peptide hormone antisera for adequate diagnosis. About 50% of all insulin-producing insulomas are endowed with stromal amyloid deposits, which chemically are composed of a peptide designated islet amyloid polypeptide. This molecule has been observed by electron microscopical immunocytochemistry to occur exclusively in the beta-cells and is co-stored with insulin in the beta-cell granules.

Endocrine cell hyperplasia and appendiceal carcinoids

As endocrine tumours in a number of organs may arise in a background of hyperplasia, the density of endocrine cells in appendices from ten patients with carcinoid tumours was compared with that in appendices from ten age- and sex-matched control patients. Crypt and lamina propria endocrine cells were quantified separately. The density of argentaffin endocrine cells in the crypts was significantly higher in appendices with carcinoid tumours when compared with the controls. No difference was found in non-argentaffin endocrine cells, and no difference was found in either argentaffin or argyrophil endocrine cells in the lamina propria. While it is possible that carcinoid tumours induce an increase in the number of enterochromaffin (EC) cells in the background mucosa, it is considered more likely that EC cell hyperplasia predisposes to the development of carcinoid tumours of the appendix.

A case of multiple carcinoid tumors of the rectum with extraglandular endocrine cell proliferation

A case of multiple carcinoid tumors of the rectum with numerous proliferations of extraglandular endocrine cells is reported. The patient was 52-year-old man with five polypoid lesions in the rectum. The resected rectum contained five macroscopic carcinoid tumors, 36 microcarcinoids, and innumerous extraglandular endocrine cell proliferations. Endocrine cell microproliferations, in their early stage consisting of one to 15 micronests, were mainly located within the bundles of muscularis mucosae, having no contact with mucosal glandular structures. All of the immunohistochemically examined proliferations of extraglandular endocrine cells contained S-100 protein-positive dendritic cells, and some endocrine cells coexisted with submucosal ganglion cells. In contrast, there was no increase in intraglandular endocrine cells. The origin of rectal carcinoid tumor may be the extraglandular endocrine cells, a distinct compartment of mucosal endocrine cells of the rectum.

Adenocarcinoid tumor of appendix presenting as unilateral Krukenberg tumor

We report a case of adenocarcinoid tumor of the appendix that presented initially as a unilateral Krukenberg tumor (a signet ring cell mucinous adenocarcinoma with prominent cellular stroma). The primary tumor in the appendix was discovered 10 months later at the time of a "second look" laparotomy. The ovarian metastasis showed both goblet cell elements and tubular formations with numerous argyrophilic cells, indicating that both components of these tumors may metastasize, a finding at variance with the conclusions of some authors who suggest that only the mucinous component may metastasize. Theories of histogenesis of these tumors are discussed, and 12 previously reported cases presenting as Krukenberg tumors (all bilateral) are reviewed. Because the primary tumor in the appendix may be small and easily missed, appendectomy is recommended in all patients with Krukenberg tumors when another primary site cannot be identified at the time of surgery.

Appendicitis revisited: a comparative study of Malawian and English appendices

The incidence of appendicitis shows a marked variation between populations which has been attributed to dietary differences. Neural mechanisms and serotonin discharge from subepithelial neurosecretory cells have been previously implicated in pain referable to the appendix and appendicitis. Forty consecutive appendicectomy specimens from Malawi were studied by staining with haematoxylin and eosin, an alcian blue - PAS diastase sequence coupled with lead haematoxylin (PbH) and immunohistology for serotonin and NSE. The findings were compared with those in appendices removed at the Middlesex Hospital, London, to see if there were any differences between a population with a low risk of appendicitis (Malawi) and a high risk population (England). Acute transmural appendicitis was seen in fewer appendices from Malawi (27.5 per cent) than in English appendices (58 per cent). Subepithelial neurosecretory cells identified with PbH were present in 20 per cent of appendices from Malawi and 69 per cent of English appendices. These cells in both series showed immunohistochemical staining for serotonin. Nerve hyperplasia identified by staining for NSE in the appendix was present in 17.5 per cent and 81 per cent of non-inflamed appendices from Malawi and England respectively. Appearance of subepithelial neurosecretory cells and hyperplasia appear to be concomitants of an increased risk of appendicitis. Neural mechanisms may participate in adapting to a low residue diet and in some cases may generate appendicitis.

Giant appendicular neurofibroma. A light and immunohistochemical study

A case of solitary appendicular neurofibromatosis is presented. The neurogenous nature of the lesion was emphasized by the positive reaction for S-100 protein. Attention is directed towards the morphological differences between neurogenous hyperplasia, which is a reactive common place feature in the elderly, and the present example of neoplastic nerve growth, which produced a gigantic appendix. A review of the literature failed to disclose any previous case unassociated with von Recklinghausen's disease.

Neurogenous hyperplasia leading to appendiceal obliteration: an immunohistochemical study of 237 cases

A series of 237 appendices was studied immunohistochemically for neurogenous hyperplasia. This was observed in 195 cases. It was possible to trace a continuum from appendices with intact lumens, featuring intramucosal neurogenous hyperplasia often with co-existent submucosal and muscular nerve growth, to obliterated specimens whose axial portions were composed of varying proportions of nerve tangles and fibrous tissue. Predominantly fibrotic specimens were considered as end-stages of this process. Stromal, argyrophilic cells lying amidst the nerve elements were prominent in the early, non-obliterated cases; their number decreased in the obliterated nerve rich specimens and such cells became inapparent in the late fibrotic stage. Repeated minimal subclinical attacks of inflammation are thought to trigger this lesion.

A study of the histopathogenesis of carcinoid tumors of the small intestine and appendix

A specimen from the small intestine with multiple (three) classic carcinoid tumors and one appendiceal carcinoid tumor displaying argentaffinity, argyrophilia (Grimelius stain), and serotonin and neuron specific enolase immunoreactivity was examined by light microscopy with regard to the tumor cell histopathogenesis. The smallest tumor (diameter 0.5 cm) from the small intestine was cut into 512 and the appendiceal tumor into 511 serial sections, which were stained with the argyrophil technique. In the small intestine an increased number of endocrine cells and small proliferating aggregates of endocrine cells were observed among nonendocrine enterocytes in the crypts of Lieberkühn. They seemed to grow initially inside the crypts and to later infiltrate through the basement membrane into the lamina propria of the mucosa. This finding suggests that classic carcinoid tumors of the small intestine develop from mucosal endocrine (enterochromaffin) cells. Since proliferating argentaffin cells were also seen in the mucosal crypts in one of the other two carcinoid tumors (2 cm in diameter) in the same intestine specimen, it is suggested that when multiple carcinoid tumors occur in the small intestine they arise from multiple sites. There was no apparent connection between the mucosal crypts and the carcinoid tumor of the appendix. Thus in this particular case, the appendiceal carcinoid tumor did not appear to derive from the mucosal endocrine cells but from the subepithelial endocrine cells that are present in the lamina propria and submucosa of the appendix wall. Supporting this view is the fact that S-100 protein immunoreactive cells are found both in close relation to subepithelial endocrine cells and as an integral component of appendiceal carcinoid tumors.

Carcinoid tumour of stomach and primary hyperparathyroidism: a new association

Three cases of carcinoid tumour of the stomach associated with primary hyperparathyroidism had the clinical and pathological features of a pluriglandular syndrome. Two of the patients showed multiple small polypoid carcinoids in the non-antral stomach, in conjunction with a parathyroid adenoma in one and parathyroid hyperplasia in the other case. One of these patients was also suffering from pernicious anaemia. A third patient had a large metastasising carcinoid arising in the gastric body and a parathyroid adenoma. Immunohistochemical stains for PGP 9.5 were positive in the carcinoids of all three cases. In all cases the carcinoids showed immunoreactivity for gastrin. A positive family history of endocrine hyperplasia and neoplasia was established in one case. It is suggested that patients with gastrointestinal carcinoids and their families should be evaluated for hyperparathyroidism, and patients with hyperparathyroidism presenting with upper gastrointestinal symptoms should undergo endoscopy to rule out gastric carcinoid tumours.

Chronic ulcerative colitis complicated by atypical carcinoid tumour

A malignant carcinoid tumour of the rectum was found in a patient who had chronic ulcerative colitis. It had a multifocal origin and had not been macroscopically apparent. This association has been recorded in the colon. Hyperplasia of enterochromaffin cells in ulcerative colitis and also dysplasia of these elements as part of a pancellular dysplasia may occur; and this may be a possible explanation for the development of a carcinoid tumour in this condition.

Pernicious anaemia and mucosal endocrine cell proliferation of the non-antral stomach

There is a recognised association between pernicious anaemia and the development of gastric carcinoma, endocrine cell hyperplasia, and carcinoid tumour. Multiple endoscopic biopsies from the body mucosa of seven patients with pernicious anaemia showed small intestinal metaplasia with varying degrees of inflammation, fibrosis, and expansion of the lamina propria. Using conventional silver and lead stains, endocrine cells were inconspicuous. Staining for the general neural and neuroendocrine markers NSE and PGP 9.5 revealed a proliferation of endocrine cells in the epithelium and isolated clumps of endocrine cells in the lamina propria. The clumps were composed of two cell types, either small or large. Some of these endocrine cells showed gastrin, 5HT, VIP and substance P immunoreactivity of varying intensity. Ultrastructurally nine morphologically distinct types of granules were found some of which correlated with the immunohistochemistry. Some separate islands were composed solely of endocrine cells while others had a definite neural component, suggesting that the former arise from 'budding off' of enteroendocrine cells and the latter originate from the neuroendocrine cells of the lamina propria plexus. Thus there may be a dual origin of carcinoid tumours. Carcinoid tumours associated with pernicious anaemia tend to be multifocal and are infrequent. Less than 50 such cases have hitherto been reported. Our findings of endocrine cells proliferations in seven cases of pernicious anaemia indicate that this may be an adaptive change that occurs frequently and provides the basis on which carcinoids, less frequently, develop.

Subepithelial neuroendocrine cells and carcinoid tumours of the human small intestine and appendix. A comparative immunohistochemical study with regard to serotonin, neuron-specific enolase and S-100 protein reactivity

A comparative immunocytochemical study was performed of subepithelial neuroendocrine cells of the human small intestine and appendix and carcinoid tumours of these sites, using a monoclonal antibody to serotonin and polyclonal antisera against neuron-specific enolase (NSE) and S-100 protein. Subepithelial neuroendocrine cells were easily identified in the lamina propria of the appendix. These cells, which sometimes occurred in aggregates, displayed serotonin and NSE immunoreactivity and were surrounded by S-100 protein immunoreactive cells, presumably of Schwann cell origin. In the appendix scattered cells with corresponding morphological features and immunoreactivity were also observed deep in the submucosa. In addition, subepithelial neuroendocrine cells were sparsely present in the lamina propria of the small intestine, occurring only as single cells in the deeper part of the mucosa below or between the epithelial crypts. Most appendiceal carcinoid tumours (11 of 12 examined cases) were biphasic and consisted of neuroendocrine tumour cells with intermingled S-100 protein immunoreactive cells (Schwann cells) with long cytoplasmic extensions. However, small intestinal (11 cases) and caecal (10 cases) carcinoids lacked S-100 protein immunoreactive cells as an integral component. The results indicate that the appendiceal carcinoids are mostly closely related structurally to the subepithelial neuroendocrine and Schwann cell aggregates of the lamina propria and are thus presumed to be histogenetically related to this cell system, while the histogenesis of small-intestinal and caecal carcinoids remains less clear.

Ultrastructural study on an appendiceal carcinoid tumor showing intra-nerve fiber growth

Ultrastructural and immunohistochemical studies on an appendiceal carcinoid tumor in a 53-year-old man disclosed an intimate association of nerves and tumor cells. Electron microscopy revealed that the tumor nests were composed of neurosecretory cells containing neurosecretory granules and peripherally-located Schwann cells encasing axons. Some tumor nests were continuous with nerve fibers invested in the common basal lamina. These findings suggest that at least some carcinoid tumors of the appendix show intra-nerve fiber growth, and that the neurosecretory cells might be present in the nerve fibers from the beginning or infiltrated into the nerve fibers at a very early stage of neoplastic transformation.

PGP 9.5, a new marker for human neuroendocrine tumours

PGP 9.5 is a soluble protein isolated from brain and is a general marker for neuronal and neuroendocrine tissue. Its function is not known. Until now neurone specific enolase (NSE) has been the only general marker for the paracrine system and tumours derived from it. Seventy-four neuroendocrine tumours, 17 melanocytic naevi, 51 melanomas and four granular tumours were stained immunohistochemically for PGP 9.5 and NSE. A variety of pulmonary and non-neuroendocrine tumours were also stained. Two so-called goblet cell carcinoids of the appendix were included in the series. Using NSE 59/74 neuroendocrine tumours were positive and 58/74 stained for PGP 9.5. In combination 63/74 of these tumours were positive for either NSE or PGP 9.5 or both. Staining for PGP 9.5 was better for demonstration of nerves in routinely processed material than was staining for NSE. Twenty-one out of 43 primary melanomas stained for PGP 9.5 and 36 showed staining for NSE. Only two of eight metastatic melanomas melanocytic stained for PGP 9.5 while seven of these eight stained for NSE. Six of 17 melanocytic naevi stained for PGP 9.5 and five stained for NSE. All four granular cell tumours stained for PGP 9.5 and NSE. Both "goblet cell carcinoids' of the appendix were negative for NSE and PGP 9.5. Fifteen out of 32 pulmonary cancers showed staining for either marker and no non endocrine tumour showed any specific staining. Staining for PGP 9.5 is a valuable additional probe in the exploration of the paracrine system and the diagnosis of tumours arising from it.