6-year-old, male neutered Great Dane

• Large volume echogenic peritoneal effusion
• Multifocal soft tissue nodules are associated with the serosal margin of small intestines
• A sheet of soft tissue mass/masses is present in the near field, associated with the ventral peritoneal lining
• The near field imaging of the spleen suggests a large, mottled spleen; the spleen has  nodules on its serosal margin, similar to those on small intestines

Synthesis:

1. Large volume echogenic effusion
2. Numerous peritoneal nodules
3. Sheets of nodules/masses associated with the ventral peritoneal cavity
4. Diffuse hepatopathy with mottled architecture and nodules/masses

• Despite the history of corncob foreign body, disseminated neoplastic processes are prioritized (carcinomatosis).  A component of septic peritonitis could also be considered for such echogenic peritoneal effusion, but would not necessarily explain the peritoneal nodules/masses

• Two corn cobs are in a non-distended stomach
• Multifocal soft tissue nodules and masses are present throughout the peritoneum, surrounding peritoneal effusion, most notable along the ventrolateral peritoneal cavity; some of the sheetlike masses of the cranial abdomen are mineralized and continuous with masses of the caudoventral pleural cavity (limited exam of the thorax)
• Moderate to severe multifocal abdominal lymphadenopathy is most severe at the porta hepatis and right medial iliac lymph node
• The prostate is large, irregular in shape and heterogenously contrast enhancing
• Multifocal hypoattenuating cortical defects are present in the kidneys (infarcts)

CT Diagnosis:

• Disseminated peritoneal and pleural neoplasia, lymphadenopathy, and bicavitary effusion.
• Large irregular prostatic mass
• Non-obstructive gastric corn cob foreign bodies
  • The combination of findings is most suggestive of carcinomatosis and lymph node metastasis originating from a primary neoplasm in the prostate

Sampling of numerous abnormalities was performed over several days:

• Abdominal Effusion Cytology Sample #1 (7/28/22, 9:21AM):
  • Eosinophilic and mixed cell inflammation with atypical tissue cell proliferation; suspected markedly reactive mesothelial hyperplasia.
• Abdominal Effusion Cytology Sample #2 (7/29/22, 3:32PM):
  • Abdominal effusion sampling of marked eosinophilic and mixed cell inflammation with reactive mesothelial hyperplasia.
• Prostate Cytology (7/30/22, 9:48AM):
  • Large cell lymphoma
• Right Medical Iliac Lymph Node Cytology (7/30/22, 9:48AM):
  • Spindle cell proliferation with mild neutrophilic and macrophagic inflammation.
• Abdominal Effusion Cytology Sample #3 (8/12/22, 9:46AM):
  • Exudate, moderate neutrophilic, mild to moderate eosinophilic, and mild lymphocytic and macrophagic inflammation.
• Abdominal Effusion Cytology Sample #4 (8/12/22, 10:10AM):
  • Marked neutrophilic, moderate eosinophilic, and mild macrophagic inflammation with low numbers of atypical cells.
• Incisional Biopsy of Peritoneal Nodules (8/12/22, 5:55PM)
  • Pyogranulomatous and mild lymphoplasmacytic peritonitis

The dog was treated with steroids after these diagnostics were performed; there was no further follow-up at the Animal Medical Center. The dog presented DOA at the referral hospital 2 months after the initial ultrasound.

A definitive diagnosis proved challenging, especially considering our initial suspicion of carcinomatosis associated with prostatic neoplasia ¹.  The effusion never provided a diagnosis of neoplasia.  Based on the diagnosis of lymphoma from the prostate, we can surmise that the disseminated nodules/masses may be a sign of lymphomatosis.

In humans, as in dogs, malignant neoplasia causing peritoneal effusion and peritoneal nodules/nodules is most often associated with carcinomatosis, with lymphomatosis being rare.² Other disease processes that can mimic carcinomatosis in people include pseudomyxoma peritonei, peritoneal lymphomatosis, peritoneal malignant mesothelioma, and leiomyomatosis peritonealis disseminata.³   The CT appearance of lymphomatosis can overlap with carcinomatosis and sarcomatosis.⁴ Lymphomatosis may be more likely if the lymph node involvement is diffuse throughout the abdomen, not localized to one particular region or one abnormal organ.  The peritoneal lesions of lymphoma tend to be “bulky and homogenous” rather than multiple small nodules seen in peritoneal carcionomatosis.  In our case, the lymphadenopathy was most certainly multifocal, throughout the abdomen (not limited to the prostate).  However, the peritoneal masses were a combination of bulky, “caked-on” masses as well as small nodules.^4,5

The ultrasound description of abdominal carcinomatosis in dogs and cats have been described in numerous publications.^7,8,9 Regional organ-associated masses or nodules as well as aggregated bowel and peritoneal thickening were more associated with peritoneal neoplasia whereas localized, severely complex fluid collections were more associated with inflammatory peritoneal disease. Interestingly, the cytological evaluation of the peritoneal and pleural effusion in this case was consistently inflammatory, failing to yield neoplastic cells.  The cytologically interpretable yield for ultrasound-guided fine-needle sampling of carcinomatosis was 72.3% in one study ⁹ with no difference between cats and dogs, making this a worthwhile clinical procedure for most cases.