DSRCT is an exceptionally rare malignancy, first described by Gerald and Rosai in 1989 [1
]. Characterized by a predilection for young males, it typically presents as an intra-abdominal mass with multiple intra-peritoneal implants, and has a 5-year survival rate of 15% [2
]. Our patient died approximately 7 months following the onset of symptoms.
As with all medical diagnoses, that of DSRCT involves a thorough history, physical examination and series of investigations. Our patient certainly did not fit the usual demographics for DSRCT, a disease that typically affects adolescents and young adults. However, his clinical findings of abdominal pain, anorexia, and ascites, though non-specific for DSRCT, represent three of the more commonly described signs and symptoms of this malignancy [3
In Cao et al. report of 18 DSRCT cases, five of the patients presented with ascites [3
]. Lae et al. documented ascites occurring in only two of 18 DSRCT cases [4
]. Thus, ascites is a clinical component of this disease, though it rarely occurs in isolation. Furthermore, ascites has a broad differential diagnosis which warrants a methodical workup.
Cirrhosis accounts for more than 85% of cases of ascites, with the remaining 15% caused by congestive heart failure, malignancy, and other less common diseases. Malignancy accounts for approximately two-thirds of non-cirrhotic ascites [5
]. When confronted with ascites, a thorough clinical history is essential in differentiating hepatic from non-hepatic causes. A discussion of risk factors for liver disease, including alcohol use and viral hepatitis, as well as a history of cardiac disease should be sought. An episode of new onset ascites accompanied by abdominal pain is suspicious for malignancy [6
Physical examination is equally important in the workup of ascites. Fluid wave and shifting dullness are among the most specific markers of ascites (90% and 72%, respectively), whereas flank dullness, bulging flanks, and shifting dullness are the most sensitive (84%, 81%, and 77%, respectively) [7
]. Examination beyond the abdomen may demonstrate palmar erythema, gynecomastia, and spider nevi, suggestive of liver disease. An elevated jugular venous pressure suggests congestive heart failure or constrictive pericarditis. Generalized edema, particularly of the face and upper limbs, suggests nephrotic syndrome. The absence of these unique clinical findings pushes more towards a malignant etiology.
Malignant ascites often occurs when the malignancy is advanced or recurrent. Urinary bladder and ovarian malignancies, as well as cancers of the colon, stomach and pancreas can cause peritoneal carcinomatosis with associated ascites [8
]. DSRCT is an exceedingly rare cause of malignant ascites. However, features of ascitic fluid can narrow the differential within this malignancy-related group.
Ascitic fluid analysis should be routinely performed in any patient with new-onset ascites. 20 mL of fluid should be placed in two blood culture bottles at the bedside, and another 10 mL should be sent for cell count and albumin. Fluid cytology may be ordered if malignancy is high on the differential. A serum albumin should be drawn at the same time.
The gross appearance of ascitic fluid can be modestly helpful in elucidating the etiology. 20% of malignant ascites fluid is grossly bloody, as in our case, though more than half of such cases are due to hepatocellular carcinoma [8
]. Only 5% of cirrhotic ascites is bloody. Cell count and differential are useful in identifying spontaneous bacterial peritonitis, although the white cell count is generally also elevated in malignancy-related ascites [6
]. Cytology may be extremely valuable in suspected malignancy, being positive in 97-100% of cases of peritoneal carcinomatosis, but was surprisingly negative in our case [6
The SAAG, a parameter of oncotic pressure gradient, has been used for more than two decades to distinguish portal hypertension-related ascites from all other causes with a diagnostic accuracy of 97% [5
]. An elevated SAAG (11 g/L or greater) correlates with portal hypertension, whereas a low gradient indicates no portal hypertension. Table outlines common pathologies associated with both high and low SAAG values [6
]. In our case, a SAAG of 8 g/L, when combined with the patient's clinical features, certainly favoured a malignant diagnosis.
Ascites Etiologies by Serum-Ascites Albumin Gradient (SAAG)
Tumour analysis, most notably immunohistochemical and cytogenetic studies, has enhanced our ability to diagnose DSRCT and has identified it as a unique clinical entity. Microscopically, the biopsy samples in our case fit the well-documented description of small round blue tumour cells, although there was minimal surrounding desmoplastic stroma. Typically, the tumour cells are separated by plentiful stroma [9
Histologically and cytogenetically, DSRCT shares features with other round cell tumours including small cell carcinoma, mesothelioma, Wilms' tumour, and Ewing's sarcoma/peripheral neuroectodermal tumours (PNET). DSRCT cells are normally reactive for keratin, epithelial membrane antigen, desmin, vimentin, and neuron-specific enolase [4
]. Small cell carcinoma often lacks desmoplastic stroma and is not immunoreactive with desmin [16
]. In our case, desmin was positive and demonstrated the unique punctate and cystoplasmic staining. Interestingly, WT1 was negative, a finding unusual for DSRCT. More than 70% of DSRCT cases are positive for WT1 [17
], a finding which has also been shown with mesothelioma and Wilms' tumour [18
]. Mesothelioma can often be distinguished by positive calretinin expression [17
], while Wilms' tumour lacks the characteristic chromosomal translocation and occurs in a much younger patient population [9
]. In our patient, cytogenetic studies revealed the typical t(11;22) translocation involving the short arm of chromosome 11. Ewing's sarcoma, which shares many features with DSRCT, is distinguished by a similar translocation which instead involves the long arm of chromosome 11 [21