What Is Your Diagnosis?

Ronan A. Mullins Section of Veterinary Clinical Sciences, School of Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland.

Search for other papers by Ronan A. Mullins in
Current site
Google Scholar
PubMed
Close
 MVB
,
Chiara Bergamino Section of Veterinary Clinical Sciences, School of Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland.

Search for other papers by Chiara Bergamino in
Current site
Google Scholar
PubMed
Close
 DVM
, and
Barbara M. Kirby Section of Veterinary Clinical Sciences, School of Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland.

Search for other papers by Barbara M. Kirby in
Current site
Google Scholar
PubMed
Close
 DVM, MS

History

An 8-year-old 45-kg (99-lb) spayed female Labrador Retriever was referred because of a large, slowly expanding subcutaneous mass in the left cranioventral aspect of the abdominal wall. The mass was initially detected 11 months prior to hospital admission during a routine physical examination performed by the dog's primary veterinarian. Prior to referral, abdominal radiography revealed a large, ovoid, homogenous mass of fat opacity superimposed on the cranioventral aspect of the abdomen. Ultrasonography of the mass had revealed a well-defined, homogeneous, mildly echogenic mass that was consistent with adipose tissue and suspected to be located within the abdominal cavity.

Findings on physical examination were unremarkable, with the exception of obesity (body condition score, 4.5 to 5/5), the presence of a large (approx 15-cm-diameter) well-defined subcutaneous mass located in the left cranioventral aspect of the abdominal wall, and several other smaller soft subcutaneous masses palpable throughout the body.

Cytologic examination of fine-needle aspirates obtained from the mass revealed several clusters of adipocytes, with abundant poorly staining cytoplasm and peripherally located round-to-oval nuclei, supportive stromal tissue, and numerous long winding capillaries, with elongate nuclei and occasional entrapped erythrocytes. No inflammatory cells, microorganisms, or features of malignancy were identified.

No abnormalities were detected on hematologic evaluation. Serum biochemical analysis revealed moderate increases in alkaline phosphatase (845 U/L; reference range, 0 to 82 U/L), alanine aminotransferase (228 U/L; reference range, 0 to 36 U/L), lipase (387 U/L; reference range, 0 to 130 U/L), and amylase (1,802 U/L; reference range, 400 to 1,300 U/L) activities and cholesterol (10.72 mmol/L; reference range, 3.2 to 6.5 mmol/L) concentration. Urinalysis of a free-catch urine sample revealed 3+ protein, 1+ epithelial cells, leukocytes, and casts. The urine protein-to-creatinine ratio was high (4.4; reference range, < 0.5), although urine bacteriologic culture results were negative. No abnormalities were detected on ACTH stimulation, low-dose dexamethasone suppression, and thyroid function testing.

The dog was anesthetized, and plain and contrast CT of the caudal portion of the thorax and abdomen was performed (Figure 1).

Figure 1—
Figure 1—

Precontrast left parasagittal (A), dorsal plane (B), and transverse plane (C) CT images and postcontrast transverse plane (D) CT image of the abdomen and thorax of an 8-year-old 45-kg (99-lb) spayed female Labrador Retriever that was referred because of a large, slowly expanding, subcutaneous mass in the left cranioventral aspect of the abdominal wall. In all images, cranial (A) or right (B, C, and D) is to the left. Images are displayed in a soft tissue window (slice thickness, 2 mm; window width, 350 Hounsfield units [HU]; window level, 63 HU).

Citation: Journal of the American Veterinary Medical Association 250, 6; 10.2460/javma.250.6.615

Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →

Imaging Findings and Interpretation

A large (18 cm in length × 17 cm in width × 12 cm in height), ovoid, well-circumscribed fat-attenuating (−110 Hounsfield units [HU]), extraperitoneal mass is located between the muscles of the left cranioventral aspect of the abdominal wall, creating a marked mass effect on the adjacent peritoneal and extraperitoneal structures. The mass contains a number of well-defined, linear, thin, and uniform soft tissue–attenuating (30 HU) septa of variable orientation and length (Figure 2). There is dorsomedial displacement of the left 7th to 12th ribs, focally deforming the outline of the thoracic cage. The left medial and lateral liver lobes and the head of the spleen are dorsally displaced, whereas the splenic body and tail are displaced caudally. The intestinal loops and gastric fundus are displaced dorsally and toward the right. No mineralization or areas of necrosis are evident within the mass. Following IV administration of nonionic, water-soluble contrast medium (ioversol, 2 mL/kg), there is no contrast enhancement of the septa or fat-attenuating component of the mass.

Figure 2—
Figure 2—

Same CT images as in Figure 1. A—Notice the large, well-defined fat-attenuating mass (asterisk) in the cranioventral aspect of the abdomen. Soft tissue–attenuating septa are visible within the mass (arrow). The left medial and lateral liver lobes and the head of the spleen (pound sign) are dorsally displaced, and the splenic body or tail is displaced caudally (arrowhead). The intestinal loops and gastric fundus (double dagger) are displaced dorsally. B—The fat-attenuating mass (asterisk) is extraperitoneally located between the muscles of the left cranioventral aspect of the abdominal wall. The gastric fundus (dagger) and the intestinal loops are displaced toward the right (arrow), and the splenic body or tail is displaced caudally (arrowhead). C—There is a large, well-defined fat-attenuating mass (asterisk) causing dorsomedial displacement of the left 7th to 12th ribs. Septa of soft tissue attenuation are visible within the mass (arrows). D—There is no contrast enhancement of the fat-attenuating mass (asterisk).

Citation: Journal of the American Veterinary Medical Association 250, 6; 10.2460/javma.250.6.615

Treatment and Outcome

The dog underwent general anesthesia and midline celiotomy. An incision was made in the linea alba from the xiphoid to pubis, and dissection between aponeuroses of the left abdominal wall was performed. A large, well-defined, smooth-surfaced, encapsulated mass was identified between the transversus abdominis and obliquus internus abdominis muscles. The mass was easily excised with blunt finger dissection. Following removal of the mass, the ribs returned to their normal position. A closed suction drain was inserted into the resultant dead space between the left transversus abdominis and obliquus internus abdominis muscles to prevent seroma formation after surgery. The mass was not submitted for histologic analysis on the basis of financial constraints, cytologic results consistent with benign adipose tissue, and absence of any gross evidence of tumor invasion at the time of surgery. Follow-up telephone conversation with the owner at 5 months after surgery revealed complete healing of the celiotomy incision and no signs of tumor recurrence.

Comments

To the authors’ knowledge, intermuscular lipomas located between the muscles of the abdominal wall have not been previously reported in the veterinary literature. The CT findings in the dog of the present report were consistent with previously reported intermuscular lipomas in dogs involving the thoracic and pelvic limbs.1 The mass appeared as a well-circumscribed fat-attenuating mass (< 20 HU), with no evidence of invasion into surrounding structures (eg, adjacent muscle). In contrast, infiltrative lipomas are characteristically hypoattenuating, similar to usual subcutaneous fat, but are often associated with fine linear striations in adjacent muscle, indicating infiltration.2 Limited CT descriptions of liposarcomas are found in the veterinary literature; however, in humans, well-differentiated liposarcomas have a relatively characteristic appearance, consisting predominantly of adipose (> 75%) and nonadipose (septa, nodules, and globular areas) components.3 The presence of soft tissue–attenuating (30 HU) septa within the mass has previously been described in both benign and malignant lipomatous lesions in humans and intermuscular lipomas in dogs and is believed to represent fibrous tissue of the intermuscular space.1,4 Although the presence of thin septa is not specific to lipomas or well-differentiated liposarcomas in humans, the latter rarely demonstrate thin septa (< 10%). On the contrary, the presence of thick septa is a significant predictor of malignancy.5

Computed tomography proved instrumental for several reasons in the case described in the present report; it allowed exact determination of the anatomic location and extent of the mass and its relationship with surrounding structures, and guided the surgical approach. On initial palpation, the lipomatous mass was suspected to be in a subcutaneous location, although an intra-abdominal location could not be excluded.6

Surgical removal of the lipomatous mass in the dog of the present report was achieved by standard midline celiotomy and dissection between the aponeuroses of the transversus abdominis and obliquus internus abdominis muscles; it also permitted direct and easy access to the mass and its uncomplicated removal. This surgical approach, guided by CT imaging findings, avoided dissection between muscle fibers that would have resulted following incision directly over the mass in anticipation of the existence of a simple subcutaneous lipoma. Differentiation between intermuscular, invasive (intramuscular), and simple subcutaneous lipomas can only be made on the basis of findings on advanced imaging (eg, CT or MRI), direct examination during surgery, and histologic examination.1

At the time of referral, radiography or ultrasonography was not repeated because of the limitations of these modalities in differentiating between benign lipomatous lesions and evaluating local invasion. Radiographically, intermuscular, infiltrative (intramuscular), and simple lipomas all appear as fat-dense masses.1,2 Ultrasonographically, although the 3 lesion types can vary considerably in echogenicity, the presence of hyperechoic capsules, hyperechoic stripes or striations, and sharp borders are common features among all, making differentiation challenging.7

In a previous study1 on removal of benign intermuscular lipomas, recurrence was not reported following removal, with median follow-up times of 12 to 17 months. At 5 months after surgery, the dog of the present report had complete healing of the celiotomy incision and no signs of tumor recurrence.

References

  • 1. Case JB, MacPhail CM, Withrow SJ. Anatomic distribution and clinical findings of intermuscular lipomas in 17 dogs (2005–2010). J Am Anim Hosp Assoc 2012; 48:245249.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 2. McEntee MC, Thrall DE. Computed tomographic imaging of infiltrative lipoma in 22 dogs. Vet Radiol Ultrasound 2001; 42:221225.

  • 3. Peterson JJ, Kransdorf MJ, Bancroft LW, et al. Malignant fatty tumors: classification, clinical course, imaging appearance and treatment. Skeletal Radiol 2003; 32:493503.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4. Nishida J, Morita T, Ogose A, et al. Imaging characteristics of deep-seated lipomatous tumors: intramuscular lipoma, intermuscular lipoma, and lipoma-like liposarcoma. J Orthop Sci 2007; 12:533541.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 5. Kransdorf MJ, Bancroft LW, Peterson JJ, et al. Imaging of fatty tumors: distinction of lipoma and well-differentiated liposarcoma. Radiology 2002; 224:99104.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 6. Mayhew PD, Brockman DJ. Body cavity lipomas in six dogs. J Small Anim Pract 2002; 43:177181.

  • 7. Volta A, Bonazzi M, Gnudi G, et al. Ultrasonographic features of canine lipomas. Vet Radiol Ultrasound 2006; 47:589591.

Contributor Notes

Address correspondence to Dr. Mullins (ronan.mullins@ucdconnect.ie).
  • Figure 1—

    Precontrast left parasagittal (A), dorsal plane (B), and transverse plane (C) CT images and postcontrast transverse plane (D) CT image of the abdomen and thorax of an 8-year-old 45-kg (99-lb) spayed female Labrador Retriever that was referred because of a large, slowly expanding, subcutaneous mass in the left cranioventral aspect of the abdominal wall. In all images, cranial (A) or right (B, C, and D) is to the left. Images are displayed in a soft tissue window (slice thickness, 2 mm; window width, 350 Hounsfield units [HU]; window level, 63 HU).

  • Figure 2—

    Same CT images as in Figure 1. A—Notice the large, well-defined fat-attenuating mass (asterisk) in the cranioventral aspect of the abdomen. Soft tissue–attenuating septa are visible within the mass (arrow). The left medial and lateral liver lobes and the head of the spleen (pound sign) are dorsally displaced, and the splenic body or tail is displaced caudally (arrowhead). The intestinal loops and gastric fundus (double dagger) are displaced dorsally. B—The fat-attenuating mass (asterisk) is extraperitoneally located between the muscles of the left cranioventral aspect of the abdominal wall. The gastric fundus (dagger) and the intestinal loops are displaced toward the right (arrow), and the splenic body or tail is displaced caudally (arrowhead). C—There is a large, well-defined fat-attenuating mass (asterisk) causing dorsomedial displacement of the left 7th to 12th ribs. Septa of soft tissue attenuation are visible within the mass (arrows). D—There is no contrast enhancement of the fat-attenuating mass (asterisk).

  • 1. Case JB, MacPhail CM, Withrow SJ. Anatomic distribution and clinical findings of intermuscular lipomas in 17 dogs (2005–2010). J Am Anim Hosp Assoc 2012; 48:245249.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 2. McEntee MC, Thrall DE. Computed tomographic imaging of infiltrative lipoma in 22 dogs. Vet Radiol Ultrasound 2001; 42:221225.

  • 3. Peterson JJ, Kransdorf MJ, Bancroft LW, et al. Malignant fatty tumors: classification, clinical course, imaging appearance and treatment. Skeletal Radiol 2003; 32:493503.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4. Nishida J, Morita T, Ogose A, et al. Imaging characteristics of deep-seated lipomatous tumors: intramuscular lipoma, intermuscular lipoma, and lipoma-like liposarcoma. J Orthop Sci 2007; 12:533541.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 5. Kransdorf MJ, Bancroft LW, Peterson JJ, et al. Imaging of fatty tumors: distinction of lipoma and well-differentiated liposarcoma. Radiology 2002; 224:99104.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 6. Mayhew PD, Brockman DJ. Body cavity lipomas in six dogs. J Small Anim Pract 2002; 43:177181.

  • 7. Volta A, Bonazzi M, Gnudi G, et al. Ultrasonographic features of canine lipomas. Vet Radiol Ultrasound 2006; 47:589591.

Advertisement