mesenchymal hamartomas ( mh ) are the second most common benign tumors of the liver in the pediatric age group and represent about 6% of all the primary hepatic tumors . a hepatoblastoma ( hb ) is the most common primary hepatic tumor in children , with 68% of cases manifesting in the first 2 years of life . on fine - needle aspiration ( fna ) a 9-month - old male infant presented to the pediatric outpatient department with complaints of progressively increasing abdominal distension since birth along with vomiting since 2 months . contrast - enhanced computed tomography ( cect ) abdomen revealed a large complex solid cystic lesion approximately 300 ( craniocaudal )  148 ( anteroposterior )  103 ( transverse ) mm abutting the undersurface of the right lobe of the liver . it was extending till the pubic symphysis inferiorly , crossing the midline and displacing intestinal loops laterally to the left . the possibilities of mh , hb , and undifferentiated embryonal sarcoma ( ues ) were considered radiologically . the serum alpha - fetoprotein ( afp ) levels were elevated , being 334.22 ng / ml ( normal : less than 10 ng / ml ) . the ultrasound - guided fna performed from the mass yielded 10 ml blood - mixed fluid and showed the presence of few loosely cohesive clusters of small round cells showing overlapping and vague acinar arrangement focally [ figure 1 ] . these cells had high nuclear / cytoplasmic ratios , indistinct cell boundaries , scant cytoplasm , and inconspicuous 0 - 1 nucleoli [ figure 2 ] . however , no spindle cells ( mesenchymal component ) , extramedullary hematopoiesis , necrosis , giant cells , hyaline globules , myxoid connective tissue , or mitosis was seen , thus ruling out the possibilities of mh and ues . loosely cohesive clusters comprised of small round cells with vague acinar arrangement present in a hemorrhagic background ( giemsa , 100 ) the individual cells comprising the clusters had high nuclear / cytoplasmic ratio , indistinct cell boundaries , scant cytoplasm , and inconspicuous 0 - 1 nucleoli . these cells were forming vague acini at places ( giemsa , 400 ) based on the clinicoradiological findings , cytological findings , and raised serum afp levels , a possibility of small round cell tumor , possibly hb , was given . thus after approximately 1 month , the liver mass was resected and sent for the histopathological evaluation . it was received in an already cut - open state , and was unencapsulated , gray - brown in color , measuring 14 cm  12 cm  8 cm in size . the cut surface was cystic - solid with a large cyst in the center measuring 7 cm in diameter , filled up with hemorrhagic fluid . the solid area surrounding it showed alternate dark brown ( congested ) and light areas , along with multiple cysts embedded in it varying in size from 0.2 cm to 0.5 cm and filled up with mucoid or hemorrhagic fluid . the microscopic sections showed unencapsulated tumor comprising multiple bile ducts , hepatocytic cords , and variably sized cysts embedded in a loose myxoid stroma with scattered infiltrate of lymphocytes and plasma cells [ figure 3 ] . bile duct proliferation in the form of numerous bile ducts was seen , with many showing branching and distorted contours . the hepatocytes , arranged in cords and small nests , were seen at the periphery of mesenchymal lobules . multiple sections taken did not show any features of hb . a final diagnosis of mh , liver was thus made . admixture of bile ducts , hepatocytic cords , and variably sized cysts seen in loose myxoid stroma along with scattered infiltrate of lymphocytes and plasma cells . the sinusoids present in between the hepatocytes showed vascular congestion ( h and e , 100 ) . left inset : cysts were lined by flat to cuboidal epithelium ( h and e , 400 ) after the histopathological diagnosis of mh , the cytological slides were reviewed again . however , no features supporting mh , such as spindle cells ( mesenchymal component ) , extramedullary hematopoiesis , myxoid connective tissue , or bile duct cells were found . our case showed few loosely cohesive clusters of small round cells showing overlapping and vague acinar arrangement focally on cytology . these cells had high nuclear / cytoplasmic ratio , indistinct cell boundaries , scant cytoplasm , and inconspicuous 0 - 1 nucleoli . various possibilities were thought based on these cytological features and radioclinical findings . these were hb , ues and mh . a hb is composed of epithelial and mesenchymal elements in varying stages of differentiation . the epithelial elements recapitulate the stages of hepatocyte development from primitive blastema through embryonal hepatocytes to fetal hepatocytes . the distinctive cytologic features of fna of hb include clusters of tumor cells showing acinar and trabecular patterns , smaller tumor cells with a high nuclear / cytoplasmic ratio and hyperchromatic nuclei having prominent nucleoli , and the presence of extramedullary hematopoiesis . another important differential diagnosis , ues shows combination of polygonal and spindle cells with few intracytoplasmic and extracytoplasmic eosinophilic globules . the polygonal cells are large , with round or lobulated nuclei , and occasionally multinucleated , with one or several nucleoli and variable cytoplasm with poorly defined borders . it varies greatly in size , from a few centimeters to up to 30 cm . seventy - five percent occur in the right side , with few occurring in the left and rarely involving both the lobes . it has been postulated that the lesion arises from the mesenchyme of the portal vein and thus represents a duct plate malformation . mh is considered under the hb family of tumors , with features of mesenchymal  epithelial transition [ under revised classification of pediatric liver cell tumors ( working formulation ) ] . on cytology , mh is characterized by the presence of clusters of predominantly bland - looking bile duct or cuboidal epithelial cells presumably arising from the lining of cystic and distorted ducts . these epithelial cells are usually seen in conjunction with single or groups of spindle stromal cells . these findings were missing in our case . because our case showed only the round cell component with high nuclear / cytoplasmic ratio with the absence of any other element on fine - needle aspirate , along with high serum afp levels , the embryonal or small - cell undifferentiated types of hb were considered as possibilities . however , of the different types of hb , mixed epithelial / mesenchymal hb is the most similar to mh , comprised of relatively bland - appearing hepatocytes ( of fetal type ) with spindle / stellate mesenchyme . however , the mesenchymal component was absolutely missing in the present case . on pathological examination , hepatocytes in a mh can be seen at the periphery as plates or in the central part of the tumor as small clusters or single cells , smaller than normal , with vacuolated cytoplasm and pyknotic nuclei . when hepatocytes are abundant , the mh can mimic a malignant or benign hepatocellular tumor , either cytologically or histologically . unal et al . and boman et al . reported similar cases of mh in the past , which were misdiagnosed as hb on fna smears . in the present case , the hepatocytes were found to be arranged as cords and small clusters at the periphery of the mesenchymal lobules on histopathological examination . thus , there is a possibility of selective sampling of this component on fna , which could have been the possible source of the round cell component on cytology slides . the selective sampling of this peripheral hepatocellular component along with raised serum afp levels and clinicoradiological findings led to a misdiagnosis of hb in the present case . unal et al . concluded that mh of the liver with increased serum afp levels can mimic hb if the cytological examination samples only the peripheral hepatocellular component of mh , thereby emphasizing the importance of knowing this in order to avoid any misdiagnosis . table 1 summarizes the comparison of cytological features between hb , mh , and ues . we would like to conclude that mh should be considered in the differential diagnosis of hepatic cystic masses on cytology even if serum afp level is elevated . it is important to note that mh is a benign tumor , while hb is a malignant tumor requiring chemotherapy . thus , a definite diagnosis is essential , requiring histopathology to avoid the unnecessary risk of chemotherapy to the patient .
the case of a 9-month - old infant who presented with an abdominal mass since birth is discussed here . fine - needle aspiration 
 ( fna ) cytology of this mass was performed , from which it was thought to be a small round tumor , possibly a hepatoblastoma ( hb ) . 
 histopathologically , however , it was found to be a mesenchymal hamartoma ( mh ) . 
 this case report thus highlights this cytological limitation .