Mastectomy in the Cat — Complete Procedure (Fossum's Small Animal Surgery)

Overview

Anatomy of the Feline Mammary Chain

• Cranial thoracic (T1)
• Caudal thoracic (T2)
• Cranial abdominal (Ab1)
• Caudal abdominal (Ab2)

• Cranial glands (T1, T2) → axillary lymph nodes
• Caudal glands (Ab1, Ab2) → inguinal lymph nodes
• There is cross-drainage between T2 and Ab1, which is why unilateral complete (radical) mastectomy is recommended in cats rather than lumpectomy or regional mastectomy.

Indications

• Solitary or multiple mammary masses
• Suspected or confirmed mammary adenocarcinoma
• Mammary hyperplasia/fibroadenomatous change (less common indication for surgery)

Preoperative Evaluation

1. Staging workup (always recommended before surgery):
   • Thoracic radiographs ×3 views (check for pulmonary metastasis — most common site)
   • Abdominal ultrasound (liver, spleen, lymph nodes)
   • Fine-needle aspirate (FNA) of regional lymph nodes
   • CBC, serum chemistry, urinalysis
2. Tumor measurement and documentation — prognostic significance:
   • < 2 cm: median survival ~3 years
   • 2–3 cm: median survival ~2 years

   • 3 cm: median survival ~4–6 months

3. Ovariohysterectomy (OHE) — often performed concurrently; early spaying reduces mammary tumor risk, but OHE at time of mastectomy has not been shown to improve survival in cats with existing tumors. However, it eliminates progesterone stimulation.

Types of Mastectomy (Fossum Classification)

Fossum's recommendation for cats: Unilateral complete mastectomy is preferred because of the high malignancy rate and intercommunicating lymphatics. This removes all ipsilateral glands, the overlying skin, and the regional (inguinal) lymph node.

Patient Preparation

• Anesthesia: standard general anesthesia protocol; cats often require careful monitoring
• Clipping and sterile prep: clip from the axilla to the inguinal region on the affected side, extending well beyond the mammary chain
• Positioning: dorsal recumbency, limbs secured cranially and caudally
• The inguinal lymph node is included in the dissection (caudal end of the chain)

Surgical Procedure — Unilateral Complete Mastectomy

Step 1: Initial Incision

• Make an elliptical skin incision surrounding all mammary glands on the affected side
• The incision should include an adequate margin of normal skin (at least 1–2 cm) around the entire chain
• Extend the incision from the axillary region cranially to the inguinal region caudally
• The ellipse should encompass the nipples and any visible masses

Step 2: Cranial Dissection

• Begin dissection at the cranial end (thoracic glands)
• Using sharp and blunt dissection, elevate the mammary tissue off the underlying external abdominal oblique muscle fascia and pectoral muscles
• The plane of dissection is between the mammary gland and the deep fascia
• Ligate or cauterize the superficial epigastric vessels (cranial and caudal superficial epigastric arteries and veins), which run along the deep surface of the mammary chain
  • Caudal superficial epigastric vessels are the major blood supply; they enter at the caudal aspect

Step 3: Caudal Dissection and Inguinal Lymph Node Removal

• Continue dissection caudally toward the inguinal region
• Identify and include the inguinal lymph node in the excised specimen — it lies in the inguinal fat pad associated with Ab2
• Ligate the caudal superficial epigastric vessels close to their origin from the femoral vessels
• Complete the caudal skin ellipse

Step 4: Axillary Region

• At the cranial end, if the axillary lymph node is enlarged or suspicious, it may be removed (though it lies deeper and is not always included in routine dissection)
• Ligate the cranial superficial epigastric vessels at the axillary end

Step 5: Hemostasis

• Achieve thorough hemostasis using electrocautery, ligatures, or hemostatic clips
• Major vessels (superficial epigastric) should be double-ligated
• Inspect the entire wound bed before closure

Step 6: Dead Space Management

• After resection, there is significant dead space
• Options:
  • Closed-suction drain (Jackson-Pratt or similar) placed subcutaneously through a separate stab incision — recommended for large excisions
  • The drain exits away from the incision line

Step 7: Wound Closure

• Subcutaneous layer: absorbable suture (e.g., 3-0 or 2-0 Monocryl or PDS) in a simple continuous or interrupted pattern to obliterate dead space
• Subcuticular layer (if tension is present): additional absorbable sutures
• Skin closure: non-absorbable monofilament (e.g., 3-0 nylon) in simple interrupted or cruciate pattern, or skin staples
• Walking sutures (tension-relieving subcutaneous sutures): placed to reduce tension on the skin closure — particularly important in cats where skin mobility is limited
• If wound closure is under excessive tension, undermining of surrounding skin edges can help; if inadequate skin remains, a skin flap or second-stage closure may be necessary

Bilateral Staged Mastectomy

• When bilateral tumors are present, perform unilateral mastectomy first, allow healing (2–4 weeks), then perform the contralateral side
• Not performed simultaneously — bilateral simultaneous mastectomy creates excessive tension and wound closure complications
• The staging interval allows vascular reorganization and reduces anesthetic/surgical risk

Intraoperative Considerations

• Specimen handling: submit entire specimen for histopathology — assess margins, lymphovascular invasion, mitotic index, histologic grade
• Sentinel lymph node: inguinal lymph node always submitted separately; axillary lymph node submitted if enlarged
• Margin assessment: surgeon should mark margins (e.g., ink or sutures) before submitting specimen

Postoperative Care

• Analgesia: multimodal — opioids (buprenorphine in cats), NSAIDs, local blocks
• E-collar (Elizabethan collar): mandatory to prevent self-trauma
• Drain management (if placed):
  • Aseptic emptying 2× daily
  • Remove when drainage < 0.5 mL/kg/day, typically 3–5 days
• Activity restriction: cage rest for 10–14 days
• Suture/staple removal: 10–14 days postoperatively
• Wound monitoring: check for seroma, dehiscence, infection

Complications

Prognosis

• Histologic grade is the most important prognostic factor
• Tumor size at surgery is strongly predictive:
  • < 2 cm → best prognosis

  • 3 cm → poor prognosis

• Lymph node involvement → significantly reduced survival
• Adjuvant chemotherapy (doxorubicin ± cyclophosphamide): may be considered for high-grade tumors with lymphovascular invasion; evidence is limited in cats

Key Points from Fossum

Fossum emphasizes that in cats, unilateral complete mastectomy is the procedure of choice because it removes all glands with shared lymphatic drainage en bloc, minimizing the risk of leaving occult tumor foci. The high malignancy rate (~90%) justifies aggressive resection. The inguinal lymph node must always be excised with the caudal glands. Bilateral disease is managed by staged procedures, not simultaneous bilateral resection.