it has been estimated that schwannomas represent only 2 - 6% of all stromal tumors of the digestive tract . there are many synonyms for neurogenic tumors of the digestive tract , namely schwannoma , neurinoma , neurogenic fibroma , neurofibroma , neurilemoma and plexiform neurofibromatosis . these different names are used with the intent of relating them to the structure from which they originate . because of the differences in the nomenclature used , it remains difficult to precisely establish the correct prevalence of primary tumors of the neural sheath . although there is some controversy regarding the cell origin , classification and correct naming of gastrointestinal tract schwannomas , there is evidence showing that these neoplasms originate from schwann cells in the neurons of the myenteric plexus . primary schwannomas of the colon and rectum , unassociated with systemic neurofibromatosis ( von recklinghausen disease ) , are extremely rare . the objective of the present paper was to present a case of benign primary schwannoma of the sigmoid colon , unassociated with von recklinghausen disease , that was histopathologically confirmed by means of an immunohistochemical panel and was successfully treated by means of videolaparoscopic colectomy . the patient was a 71-year - old woman with complaints of tenesmus and hematochezia for 4 months , associated with weight loss of 4 kg . nine months earlier she had undergone colonoscopy and a sessile polypoid lesion in the sigmoid colon , 0.5 cm in diameter , had been removed . histopathological evaluation at that time had led to the diagnosis of a hyperplastic polyp in the colon . even with endoscopic removal of the polyp she continued to present successive episodes of fresh bleeding when evacuating , and this was associated with rectal pain and tenesmus . with these complaints , she sought the coloproctology service of so francisco university , where she underwent another colonoscopy . this second examination found a reddish polypoid lesion of approximately 3 cm in diameter , located in the sigmoid colon 35 cm from the anal margin . the surface of the mucosa covering the lesion was ulcerated and it presented slight local bleeding when in contact with the apparatus . it was removed by means of loop polypectomy . conventional histopathological examination using the hematoxylin - eosin technique showed that spindle cells were present , arranged in bundles , with dense distribution of nucleus forming palisades in dense fibrillar stroma ( fig . , an immunohistochemical panel was performed for anti - cd34 antibodies , desmin , cytokeratins ( ae1/ae3 ) , ckit , chromogranin and s-100 protein . 2 ) , while the other antibodies presented negative results ( table 1 ) . with the aim of evaluating tumor growth potential , positive results were found in fewer than 5% of the fields analyzed ( one mitosis in every ten fields at high magnification ) , thus suggesting that the neoplasm had a low mitotic rate ( fig . 3 ) . the results from the histopathological and immunohistochemical examinations allowed the diagnostic conclusion that this was a case of benign schwannoma of the sigmoid colon with a histological pattern of antoni a type , with a low degree of cell proliferation ( fig . the surgical margins of the lesion removed were compromised with neoplasia , and therefore it was decided to perform video - assisted colectomy . the patient 's postoperative evolution was uneventful and she was discharged from hospital on the fourth postoperative day . histopathological examination on the resected colon confirmed that it presented a residual neoplastic lesion with the same characteristics as presented by the polyp that was removed during colonoscopy . the resected margins obtained after surgical resection were free from involvement and there was no neoplastic involvement in any of the 21 lymph nodes examined . at present , the patient is well , without any recurrence of symptom , and a control colonoscopy examination performed 15 months after the colectomy showed normal results . tumors originating from autonomous nerves of the digestive tract form a distinct but rare subcategory of stromal gastrointestinal tumors , accounting for approximately 1% of all neoplasms affecting the digestive tract . they affect men and women with equal frequency and can appear at any age , but most commonly after the sixth decade of life . when they appear in the digestive tract , the stomach and the small intestine are the segments most frequently involved , accounting for 83 and 12% of such cases , respectively . schwannomas located in the colon and rectum that are unrelated to von recklinghausen disease are extremely rare . although they usually evolve asymptomatically , they may in some cases , as in our patient , present bleeding , rectal pain and tenesmus . it is important to highlight that unspecific rectal pain is often confused with the pain of idiopathic proctalgia fugax , which may cause delay in diagnosing the condition . macroscopically , schwannomas are well - delimited , lobulated tumors that may , in larger cases , present a cystic pattern . from a microscopic point of view , schwannomas are encapsulated neoplasms and two histological growth patterns have been described : antoni a and antoni b. in antoni a type there is dense growth of fusiform cells , compactly arranged in palisades to form verocay bodies . in antoni b , the fusiform cells are more loosely distributed with rounded or elongated nuclei , with a greater quantity of myxoid stroma and xanthomatous histiocytes . these findings also include undifferentiated mesenchymal cells , smooth muscle cells , cells with neural characteristics and cells with mixed differentiation of neural / muscular type . regarding our patient , the result from the histological examination using the hematoxylin - eosin technique suggested a diagnosis of schwannoma of the sigmoid colon with a cell pattern classified as antoni a. before immunohistochemistry techniques came into routine use , schwannomas were wrongly diagnosed as smooth muscle neoplasms such as leiomyomas and leiomyosarcomas . the use of immunohistochemical panels plays a fundamental role in diagnosing schwannomas and in ruling out other neoplasms of mesenchymal origin . authors believed that positive immunostaining for s-100 protein and leu7 antigen indicated a neoplasm originating from schwann cells . strongly positive immunoexpression of s-100 protein and low affinity for cd34 , cytokeratins , smooth muscle actin and desmin confirm the possibility of schwannoma in practice . the present case was within these criteria : results identical to these were found from running the immunohistochemical panel that is most commonly proposed . the exact biological behavior of schwannomas is still not fully clear , since only a small number of cases have been published . consequently , determination of malignity becomes a difficult challenge that can not always be resolved using conventional histopathological techniques . many parameters have been studied in relation to tumor behavior and , so far , no single parameter alone allows safe prediction of the degree of malignity . a mitotic activity rate of more than five mitoses per field at high magnification and tumor size greater than 5 cm tend to be associated with a high risk of metastasis or recurrence . we evaluated the number of mitoses by means of the immunohistochemical technique using ki-67 antibodies and found a low rate of cell division , suggesting that this was a low - grade schwannoma . the low mitosis rate , the absence of atypical mitosis figures and the absence of nuclear hyperpigmentation , especially in the necrotic areas found , were also useful for characterizing the benign nature of the lesion . although schwannomas are considered to be benign tumors , their high recurrence risk must not be ignored . in a study on 303 benign schwannoma cases unrelated to von recklinghausen disease , das gupta and brasfield found that 2% of the tumors evolved with distant metastases . this evidence suggests that , despite the skepticism regarding the possibility of malignant transformation of schwannomas initially considered benign , this possibility does exist and must not be ignored . the most aggressive phenotype relates to the size of the tumor and its proliferative activity rate , and this gives rise to greater recurrence , metastases and lower overall survival rates . the best therapeutic option is complete surgical removal with margins free from neoplastic involvement . since the risk of malignant transformation is small , broad lymph node resections are not recommended . for tumors with more aggressive behavior , the same surgical criteria should be used , but greater rigor in postoperative follow - up is recommended . the surgical approach depends on the size and location of the tumor and on its histopathological pattern . minimally invasive surgery using videolaparoscopic access , such as in the present case , may be indicated for tumors located in the proximal colon and rectum . for tumors in the distal rectum , transanal endoscopic resection can be used . the use of radiotherapy or adjuvant chemotherapy still presents conflicting results and is not recommended for routine use . in conclusion , schwannomas of the colon and rectum are tumors that are rarely detected and for which the use of an immunohistochemical panel is important to achieve a definitive histopathological diagnosis . radical surgical removal is the preferred treatment because it allows improvement of overall survival and disease - free survival rates .
schwannomas are neoplasms originating from schwann cells , which are the cells forming nerve sheaths . 
 these neoplasms generally involve peripheral nerves . 
 they rarely affect the gastrointestinal tract and primary colon involvement is extremely rare . 
 the objective of the present paper was to present a case of primary schwannoma of the sigmoid colon , unassociated with von recklinghausen disease , that was histopathologically confirmed by means of an immunohistochemical panel . 
 the patient was a 71-year - old woman who had had rectal bleeding when evacuating , with pain and tenesmus , for 4 months . 
 she underwent colonoscopy , which identified a raised submucous lesion of 2.8 cm in diameter , located in the sigmoid colon , 30 cm from the anal margin . during examination , loop polypectomy with lesion excision was performed . 
 histopathological evaluation showed that this was a tumor of stromal origin . 
 its resection margins were compromised by neoplasia , and colon resection by means of videolaparoscopy was indicated . conventional histopathological examination using 
 the hematoxylin - eosin technique suggested that the neoplasm was of mesenchymal origin . 
 an immunohistochemical panel was run for etiological confirmation , using anti - cd34 antibodies , desmin , cytokeratins ( ae1/ae3 ) , ckit , chromogranin and s-100 protein . 
 the panel showed intense immunoexpression of s-100 protein . 
 investigation of the proliferative activity rate using ki-67 antibodies showed that there was a low rate of mitotic activity , thus confirming the diagnosis of primary benign schwannoma of the colon . 
 the patient 's postoperative evolution was uneventful and she remains in good health , without signs of tumor recurrence , 15 months after surgical excision .