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HISTORY

One episode of vomiting and urinary incontinence 6 months prior to presentation to UGA. She was initially seen at a referral specialty hospital, where an abdominal ultrasound was done. The conclusion was a mass originating from either pancreas or lymph node and she was treated presumptively for lymphoma. She received one round of the CHOP protocol, which did not cause a significant decrease in the size of the mass. Since, two courses of prednisone were given (2 weeks at 30mg SID, 2 weeks at 20mg SID), which finished one month prior to presentation. She has no other pertinent medical history.

PHYSICAL EXAM: T: 101.1*F (38.4 Celcius) P: 160 bpm R: 40 bpm Wt: 27.0 kg
Bright, alert, and responsive. Mucous membranes are moist and pink with a capillary refill time less than two seconds.
Grade II-III/VI left systolic murmur. Her lungs sounded normal. Her abdomen is distended but non-painful on palpation. She has a large, firm mid-abdominal mass. Her peripheral lymph nodes palpate normally . Fundic exam (retinal exam) showed retinal hemorrhage on the right and mildly tortuous vessels on the left. The remainder of the physical exam was unremarkable.

DIAGNOSTICS:

  • Complete blood count: Hct – 39.4% (normal); platelets – 570,000 (normal); neutrophils – 21,000 (elevated)
  • Serum chemistry: all within normal limits
  • Urinalysis: USG – 1.026
  • Thoracic radiographs: unremarkable, no evidence of pulmonary metastasis
  • CT: See following

Abdominal CT, pre- and post-contrast

Pre- and post-contrast CT images of the abdomen from the level of T7 through the pelvis, acquired prior to and following the intravenous administration of 68mL Iohexol (350 mgI/mL). Images were acquired in 3mm helical slices with dorsal and sagittal reformations.

FINDINGS

Within the mid and caudal retroperitoneal space, and filling the peritoneum (when the patient is in dorsal recumbency), a large, irregularly marginated mass with heterogeneous soft tissue attenuation (HU = 24-52) is present. Following contrast administration, the mass undergoes heterogeneous enhancement. The internal architecture of the mass is markedly complex and/or disorganized. In maximum dimension, the mass measures 12.7 x 13.5 x 10 cm. The mass originates in the mesentery at the level of the cranial mesenteric artery and cranial mesenteric vein. As the mass is followed caudally, it partially to completely encircles the aorta, caudal vena cava, and the medial half of the left renal vein. The caudal vena cava and medial portion of the left renal vein are severely compressed by the mass, particularly with the patient in this position. The left renal artery is displaced dorsally and follows the left dorsolateral contour of the mass. The right renal vein and artery course along the dorsocranial margin of the mass. Complete venous obstruction is not seen, based on the post-contrast images, acquired during the venous phase. There is also no definitive evidence of thrombus or tumor invasion. Branching off the left renal vein, an enlarged gonadal vein (0.6 cm) courses caudally, branches into the caudal left portion of the mass, and then adjoins the cranial aspect of the left internal iliac vein. There is also an anomalous vessel communicating with the left phrenicoabdominal, which appears to originate in a plexus of vessels on the left lateral contour of the mass. Surrounding the mass, multiple small aberrant vessels are present; most are presumed venous based on diameter. The splenic vein is diffusely moderately enlarged. Cranial to the mass, the portal vein has an atypical leftward deviation before returning to a normal position and entering the porta hepatis. The mass ends at the level of the deep circumflex vessels, which are also mildly displaced by the mass. There is rightward displacement of the small intestines and craniolateral displacement of the left kidney.

The right adrenal is distinctly seen and the caudal pole measures 8mm in diameter. The cranial pole of the left adrenal gland is distinguishable and measures 8mm in diameter. The caudal pole is not definitively identified caudal to the left phrenicoabdominal vein. At this level, the mass effaces the ventral margin of the phrenicoabdominal vein.

Two medial iliac lymph nodes are present bilaterally, and are enlarged (right – 1.7 x 1.0 cm, 0.8 x 0.9 cm; left – 1.4 x 0.9 cm, 1.3 x 1.0 cm). These undergo mild heterogeneous contrast enhancement. Small (0.2 x 0.2 cm) hypogastric lymph nodes are also present bilaterally.

Increased soft tissue attenuation is noted in the dependent areas of the lungs, consistent with positional and/or general anesthesia-induced atelectasis.

SUMMARY

Large, heterogeneously enhancing retroperitoneal soft tissue mass with infiltration around mid and caudal abdominal major vasculature and peritoneal extension.

  • Malignant neoplasia is considered primarily, with tissues of origin including ovarian/ovarian remnant (neoplasia, granuloma), retroperitoneal soft tissues (sarcoma), paraganglioma or lymph node. A mass involving the ureter cannot be definitively excluded because they were difficult to trace, but would be considered less likely because of lack of pyelectasia or hydronephrosis proximal to the mass.

Bilateral medial iliac lymphomegaly.

  • Metastatic lymphadenopathy is the primary differential, but reactive lymphadenopathy cannot be definitively excluded.

DIAGNOSIS

Following the CT examination, ultrasound-guided fine needle aspirates of the mass were performed without complication. The patient’s recovery from anesthesia was uneventful, except elevated blood pressure measures. These persisted and were also noted the following day (average BP = 230 mmHg).

Cytology:

Intact cells are round with lightly basophilic cytoplasm that occasionally contains faint, eosinophilic granules. Nuclei of intact cells are round with a coarsely stippled chromatin pattern and occasional indistinct angular nucleoli/nucleolar rings. Rare micronuclei are observed. There is minimal anisocytosis and anisokaryosis in this cell population.

Cytologically most compatible with a neuroendocrine tumor; specifically the location and the fine, eosinophilic, intracytoplasmic granules is strongly suggestive of a pheochromocytoma.

Based on the identification of the majority of the left adrenal gland and the suspicion that the mass had grown cranially around the left renal vessels, this was considered a non-resectable extra-adrenal pheochromocytoma. This is also known as a paraganglioma. However, the owners elected medical management and this could not be confirmed.

DISCUSSION

Paraganglia tissue is distributed throughout the retroperitoneum in association with the autonomic nervous system, as well as in the sympathetic ganglia of abdominal viscera. The tissue is suspected to be derived from the neural crest. Neoplasms of this tissue can be non-functional or functional; the latter can synthesize and store catecholamines. Paraganglia neoplasms manifest in 3 forms, including pheochromocytomas, extra-adrenal pheochromocytomas, and chemodectomas. In veterinary patients, the most common paraganglioma is the chemodectoma. Extra-adrenal pheochromocytomas are rare, but case reports exist of sublumbar and mediastinal paragangliomas.

Pheochromocytomas are most commonly locally invasive, with a relatively low rate of metastases (one study reported 13% of the cases had metastases. Reported sites for metastases have included regional lymph nodes, liver, lung, kidney, spleen, and bone. There is also a relatively high frequency of concurrent neoplasia (54%) in patients that have a pheochromocytoma, which most commonly has manifested as multiple endocrine neoplasia (MEN).

REFERENCES

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