CT HEAD & CERVICAL REGION: On the cranioventral margin of the left wing of the atlas there is a focus of irregularly marginated, ill-­defined periosteal new bone. Ventral to and associated with the ventral margin of the aforementioned periosteal reaction there is a discrete, peripherally enhancing, soft tissue attenuating mass measuring 19mm x 18mm x 14mm (L x W x H).

Associated with the right ventral aspect of the caudal C2 and cranial C3 endplates, there is irregularly marginated, well-­defined 10mm projection periosteal new bone. Ventral to and associated with this change there is a heterogeneously enhancing, soft tissue attenuating structure measuring 19mm x 16mm x 13mm (L xW x H).

Both medial retropharyngeal lymph nodes are markedly enlarged, irregularly marginated, and exhibit heterogeneous, but predominantly peripheral contrast enhancement with multifocal enhancing septations. On post-­contrast images the right medial retropharyngeal lymph node appears poorly encapsulated and extends laterally and ventrally into the adjacent tissues. The mandibular lymph nodes are moderately, bilaterally enlarged and exhibit heterogeneous but predominantly peripheral contrast enhancement.

At the level of the C5-­C6 intervertebral disc space within the dorsal aspect of the right semispinalis capitis (biventer cervicis) muscle there is an ovoid, mildly irregularly marginated 8.8mm x 2.3mm x 5mm (L x H x W) mineral attenuating structure. On the dorsal aspect of the left mid-­cervical region at the level of C3-­C4 intervertebral disc space there is a 5.4mm cutaneous soft tissue attenuating nodule. There patient is microchipped.

CT THORAX: Within the pulmonary parenchyma there are innumerable, smoothly marginated soft tissue attenuating nodules that measure up to 10mm in diameter. A cranial mediastinal lymph node is moderately enlarged. Multiple superficial cervical lymph nodes are asymmetrically (right > left) and moderately enlarged and exhibit heterogeneous contrast enhancement. Within the left lobe of the liver there is an irregularly marginated, mildly contrast enhancing (55 to 75 HU), hypoattenuating focus. Multiple small mineral attenuating foci are noted within the caudate lobe of the liver. An additional mineral focus is noted dorsal to the caudal vena cava.

CT ABDOMEN:

In addition to the previously noted liver findings the stomach and duodenum contain a few small mineral dense objects, consistent with non-­obstructive gastrointestinal foreign material. At the level of the L3 vertebra there is a 6.8mm wide ovoid mineral focus is noted within the left dorsal subcutaneous tissues. Incidentally, lumbar spondylosis deformans is noted.

SUMMARY:

1. Mass ventral to the left wing of atlas with associated periosteal reaction, lymphomegaly, and pulmonary nodules were thought to represent metastatic soft tissue sarcoma or carcinoma vs.  primary bone tumor (osteosarcoma, fibrosarcoma, chondrosarcoma) with metastases.
2. The well-­defined new bone with associated soft tissue mass at the level of the C2-­C3 disc space may represent spondylosis deformans (with atypical soft tissue component) or metastatic lesion.
3. Hepatic nodule may represent nodular hyperplasia (or other benign lesion) or metastatic lesion.
4. Multifocal mineral foci within muscles, subcutaneous tissues, and within the visible portion of the abdomen may represent dystrophic mineralization and are of unknown clinical significance.

Diagnosis and conclusions:

18G Tru-­cut biopsies were obtained of the cervical mass ventral to left wing of the atlas and of the left medial retropharyngeal lymph node. Metastatic squamous cell carcinoma was diagnosed on histopathology. The pulmonary nodules and multifocal lymphadenopathy (mandibular, right medial retropharyngeal, superficial cervical, cranial mediastinal) were presumed to be the result of additional metastatic lesions.

Due to the extent of disease, neither surgery nor radiation therapy were practical. The owners elected to pursue conservative management with meloxicam and omeprazole. Additional follow-­up information is not available.

Discussion:

Squamous cell carcinoma (SCC) is a common malignancy of small animals that exhibits a variety of clinical presentations. Staging recommendations for SCC often depend on the location of the primary tumor, as the metastatic potential between various primary sites varies considerably. Common primary sites for SCC include the skin, oral cavity (gingival, buccal, and lingual surfaces), nasal cavity and digits.¹ Less frequently, primary sites can include the tonsils, ear canals and salivary glands.¹ Although young animals may develop SCC, the average age of affected dogs and cats ranges from 8 to 10-­ and 10 to 12-­years-­old, respectively.¹ From a diagnostic imaging standpoint the appearance of SCC is variable, but reported computed tomographic descriptions of confirmed cases of oral SCC and oral papillary SCC include such findings as: visible mass lesion with heterogeneous post-­‐contrast enhancement; evidence of osteolysis (+/-­ osteoproliferation); and regional lymphadenomegaly.^2,3

The prognosis for SCC depends heavily on the tissue of origin. Typically, SCCs are highly locally invasive and can exhibit osteolysis when adjacent to bone.^1,2,3,4 For this reason, early surgery is often recommended as the primary intervention.¹ Radiation and other adjuvant therapies are recommended for incompletely excised tumors.¹ SCC is generally considered to be unresponsive to chemotherapy, but it may be recommended in cases where other interventions are impossible.¹ One study reports that surgery alone provides the longest disease free interval (594 days) compared with other single interventions such as RT.¹ Overall, distant metastasis is uncommon, but certain tissues of origin exhibit higher metastatic potential.¹ In particular, distant metastasis is relatively common in cases of SCC of the tonsils or digits.¹ The lungs, liver and spleen are common sites of distant metastasis for tonsillar SCC.¹ The lungs are the most common site of distant metastasis for digital SCC.

Tonsillar SCC is additionally characterized by rapidly growth and a highly locally invasive nature.⁵ Despite the high overall malignancy of tonsillar SCC, it is relatively uncommon and represents only 9% of all canine oral tumors, according to one study.⁵ Retrospective studies of tonsillar SCC cases give variable survival data, but tonsillar SCC that has metastasized to the lymph nodes generally carries a poor prognosis.^5,6 Early surgical debulking with multimodal adjuvant therapy, prior to regional lymph node metastasis, carries the best prognosis with an average survival time of 17 months.⁶

The present case demonstrates a highly malignant, metastatic presentation of SCC with associated boney invasion, lymphadenomegaly and pulmonary metastasis. All computed tomographic findings of this case were similar to those published in the literature.^1,2,3,4,5 One of the particular challenges of this case is that we were unable to identify a primary oral or pharyngeal lesion. Based on the biologic behavior and literature, a tonsillar etiology could be suspected. However, no mass lesion was identified in this region, so the location of the primary disease remains open. Because the presentation of SCC is highly variable (grossly, some SCC lesions can be confused with inflammatory or traumatic lesions), it is important to confirm a diagnosis with cytology or biopsy.¹ Depending on the primary site, staging may include diagnostic imaging of the regional lymph nodes, thorax and abdomen. In the present case, computed tomography offered an excellent overview of the extent and distribution of the pathology and allowed pragmatic treatment decisions to be made.

References:

1. Webb JL, Burns RE, Brown HM, LeRoy BE, Kosarek CE. Squamous cell carcinoma. Compend Contin Educ Vet. 2009 March; 31(3):133-­142.
2. Gendler A, Lewis JR, Reetz JA, Schwarz T. Computed tomographic features of oral squamous cell carcinoma in cats: 18 cases (2002-­2008). J Am Vet Med Assoc. 2010 Feb; 236(3):319-­325.
3. Soukup JW, Snyder CJ, Simmons BT, Pinkerton ME, Chun R. Clinical, histological, and computed tomographic features of oral papillary squamous cell carcinoma in dogs: 9 cases (2008-­2011). J Vet Dent. 2009; 30(1):18-­24.
4. Yoshikawa H, Mayer MN, Linn KA, Dickinson RM, Carr AP. A dog with squamous cell carcinoma in the middle ear. Can Vet J. 2008; 49:877-­879.
5. Mas A, Blackwood L, Cripps P, Murphy S, DeVos J, Dervisis N, Martano M, Polton GA. Canine tonsillar squamous cell carcinoma – a multi-­center retrospective review of 44 clinical cases. J Small Anim Pract. 2011 July; 52(7):359-­64.
6. Kühnel S, Kessler M. Tonsillar squamous cell carcinoma in the dog. A retrospective study of 33 cases. Tierärztliche Praxis Kleintiere. 2010; 38(6):367-­373.