charcoal was originally used for localizing a non - palpable tumor mass ( 1 ) , however , it is being increasingly used for localizing suspicious metastatic cervical lymph nodes or recurrent tumors in the thyroid bed after surgery ( 2).although , charcoal is known to be safe and stable when injected subcutaneously for preoperative tumor localization , it may cause foreign body reactions and granuloma , if it remains in situ for more than 6 months ( 1 ) . until recently , charcoal granuloma in the neck was not reported in the literature . under the approval of the institutional review board of our hospital , we reported a case of a charcoal granuloma that was suspected to be a recurrent tumor on ultrasonography ( us ) and f - fluorodeoxyglucose ( fdg)-positron emission tomography / computed tomography ( pet / ct ) , but was correctly identified after us - guided core biopsy . a 47-year - old woman was referred to our department for us - guided biopsy due to a persistent hypermetabolic nodule in the right level iv nodal station . she was diagnosed with invasive ductal carcinoma of the right breast and cervical lymph node metastasis at the right level iv ( tnm stage ; t2n3m0 ) . she had undergone breast - conserving surgery and excision of a metastatic lymph node ( fig . before excision of cervical lymph node metastasis , us - guided localization had been performed using charcoal . after surgery , she received chemotherapy and radiotherapy ( up to 50.4 gy ) for the right breast and the right lower cervical area . on her first follow - up fdg - pet / ct ( fig . 1d ) , which was performed 6 months after completion of treatment , a focal hypermetabolic lesion ( maximum standardized uptake value [ suvmax ] = 4.0 ) was noted at the lateral aspect of the previous operative bed in the right level iv . the second follow - up pet / ct examination , performed 1 year after the first follow - up pet / ct scan , showed a persistent hypermetabolic lesion ( suvmax = 4.3 ) at the same site ( fig the lesion was ovoid , measured 9.8 mm in its maximal longitudinal diameter , and had an indistinct margin from the adjacent sternocleidomastoid muscle ( fig . on pre - contrast ct , the image noise and suspicious beam hardening artifact related to overlapped clavicles and shoulder girdles , rendered identification of the lesion difficult . however , the lesion seemed to be slightly hyperdense relative to the adjacent sternocleidomastoid muscle ( mean attenuation : 89 - 100 hounsfield unit ) and did not significantly enhance after contrast administration ( fig . 1 g ) . since there was no evidence of recurrence at any other site of the body except the right side of the neck , and given the conflicting results of the previous cytological and pet / ct or chest ct examinations were , we decided to closely monitor and follow - up again 6 months later . six months later , us showed a change in the echogenicity of the nodule with no change in size , but a slight change in shape ( fig . as the morphology of the nodule changed , we could not rule out the possibility of a recurrent tumor . thus , we decided to perform a core - needle biopsy , as the previous us - guided fine - needle aspiration did not yield sufficient tissue for an accurate diagnosis . us - guided core - needle biopsy was performed thrice using an 18-g semi - automatic biopsy needle ( tsk stericut ; tsk laboratory , soja , japan ) . microscopically , these dark - pigmented specimens were foreign body granulomas that comprised extensive deposits of charcoal and multinucleated giant cells , as well as fibrosis ; no tumor cells were detected ( fig . patients who undergo surgery for malignant lesions in the neck may subsequently show benign conditions mimicking recurrent tumors . these include reactive lymph nodes , traumatic neuroma , postoperative fibrosis , and suture granuloma ( 3 , 4 , 5 ) . charcoal is originally used for localization of the non - palpable breast mass ( 1 ) . charcoal is known to be a biologically inert material when injected subcutaneously and may remain in situ for up to 60 days without triggering a foreign body reaction ( 1 ) . however , in an experimental study , charcoal particles were ingested by macrophages and very slowly carried away from the injection site , causing inflammatory processes ( 6 ) . charcoal particles that remained in the surgical bed might have facilitated an inflammatory reaction during the healing process after surgery in our patient . our patient also received radiotherapy after excision of the metastatic lymph node , possibly resulting in synergistic effects leading to fibrotic charcoal granuloma . the us features of charcoal granuloma in our report were characterized by ill - defined irregular shaped lesion with initial hyperechogenicty that changed over time , and posterior shadowing . indistinct margin and posterior shadowing of the charcoal granuloma in our patient was in accordance with the finding of charcoal granuloma in the breast ( 7 ) . conversely , our lesion was hyperechoic at first , and decreased in echogenicity over time . initial hyperechogenicity of our lesion might be a helpful finding for differentiating a tumor recurrence from a non - tumorous lesion , such as a charcoal granuloma . tumor recurrence was reported to be hypoechoic to markedly hypoechoic in the surgical bed in the post - thyroidectomy neck ( 8) . although the size of the nodule was not helpful to differentiate recurrence from benign postoperative change at one time point ( 8) , the interval change of the nodule size could become one of the important imaging findings to differentiate recurrence from benign lesion . in our case , the shape and echogenicity of the lesion was changed over time , however , the lesion did not significantly increase in size during a follow - up , which suggested a benign status . ct and fdg - pet imaging findings in our patient were consistent with those of charcoal granulomas in the peritoneal cavity related to intraoperative , intraperitoneal chemotherapy ( 9 ) . the lesions showed high attenuation on precontrast ct with no remarkable enhancement on post - contrast scans . higher attenuation of the lesion compared to the adjacent muscles might be attributed to the high concentration of carbon particles ( 9 ) . both suture granulomas and charcoal granulomas can present hypermetabolic lesions due to increased utilization of glucose by activated multinucleated giant cells ( 9 , 10 ) . therefore , such foreign body granulomas can be a common cause of false positive findings in the evaluation of tumor recurrence in the postoperative neck . ultrasonography is the first line of imaging follow - up in patients with neck dissection or thyroid surgery . suture granulomas as a result of the knotted suture materials after thyroid surgery , usually had characteristic irregularly shaped , multiple or paired central or paracentral echogenic foci > 1 mm , and heterogeneous hypo- to isoechoic lesions on us ( 4 ) . although us alone is not easy to distinguish tumor recurrence from other benign lesions , initial hyperechogenicity might be a feature of a non - tumorous condition . ct may be helpful to differentiate the 2 entities because of the hyperattenuation of the charcoal granuloma . following imaging workup , us - guided fine - needle aspiration biopsy is generally indicated for the evaluation of recurrent nodal metastases . however , as in our patient , charcoal granuloma with charcoal materials may not be diagnosed properly with fine needle aspiration cytology alone . cases suspected of charcoal granuloma are better diagnosed by us - guided core - needle biopsy . in summary , we reported us , ct , and fdg - pet / ct findings of a charcoal granuloma in the neck after excision of a metastatic lymph node resulting from breast cancer . these findings included an irregular , heterogeneous hyperechoic nodule with subsequent decreased echogenicity and development of posterior acoustic shadowing on us , a high attenuating nodule on precontrast ct and a hypermetabolic lesion on pet / ct . charcoal granulomas should be included in the differential diagnosis of incidentally detected mass - like lesions at the site of presurgical localization using charcoal .
charcoal can be used for preoperative localization of metastatic lymph nodes in the neck . 
 charcoal remains stable without causing foreign body reactions during as hort period . 
 however , foreign body reactions may develop if charcoal is left in situ for more than 6 months . 
 we reported a case of charcoal granuloma mimicking local recurrence on fluorodeoxyglucose - positron emission tomography / computed tomography and ultrasonography in a 47-year - old woman who had cervical lymph node dissection due to metastatic invasive ductal carcinoma of the breast .