Exenteration

Exenteration is a radical surgical procedure involving the complete removal of all orbital contents, including the globe, extraocular muscles, orbital fat, fascia, and often the eyelids and conjunctiva. It is distinguished from enucleation, which removes only the globe and a portion of the optic nerve, and from evisceration, which removes the intraocular contents while preserving the sclera and extraocular muscles. Exenteration is indicated for extensive orbital neoplasms, severe orbital trauma with irreparable damage, or invasive fungal infections that involve the orbit and surrounding tissues. The procedure aims to achieve complete tumor excision or debridement of nonviable tissue, with the goal of preventing local recurrence or systemic spread. It is a mutilating surgery that results in a permanent cosmetic defect, and therefore, it is reserved for cases where more conservative options are not feasible or have failed.

The primary indications for exenteration include: 1) Malignant orbital neoplasms such as osteosarcoma, fibrosarcoma, chondrosarcoma, melanoma, and squamous cell carcinoma that extensively involve the orbit and adjacent structures. 2) Invasive fungal infections, particularly Aspergillus and Penicillium species, that cause orbital mycetoma or sino-orbital aspergillosis, often in immunocompromised or young, otherwise healthy animals. 3) Severe orbital trauma resulting in massive tissue destruction, including fractures of the orbital bones, laceration of the optic nerve, and avulsion of the globe, where salvage is impossible. 4) Chronic, severe orbital cellulitis or abscessation that has failed to respond to medical therapy and surgical drainage, leading to panophthalmitis and orbital necrosis. 5) Congenital orbital malformations or severe orbital deformities that are nonfunctional and painful. 6) Recurrent orbital tumors after previous incomplete excision or enucleation. The etiological factors are diverse, but the common thread is the need for radical resection to achieve local control of a life-threatening or severely debilitating condition.

Exenteration is an uncommon procedure in veterinary ophthalmology, with no large-scale epidemiological studies available. It is performed more frequently in dogs than in cats, likely due to the higher incidence of orbital neoplasia in dogs. In dogs, the most common orbital tumors are of mesenchymal origin, including fibrosarcoma, osteosarcoma, and chondrosarcoma, which tend to occur in middle-aged to older animals (mean age 8-10 years). Brachycephalic breeds may be at increased risk for orbital trauma due to their prominent eyes and shallow orbits. In cats, orbital tumors are less common but can include squamous cell carcinoma, lymphoma, and nasal adenocarcinoma with orbital extension. Fungal orbital disease, particularly aspergillosis, is seen in young to middle-aged dogs, often in sporting or working breeds that are exposed to soil and vegetation. There is no clear sex predilection. The procedure is also performed in exotic pets, such as rabbits and birds, but with limited data. Overall, the incidence is low, but the impact on the animal's quality of life is significant, making appropriate patient selection critical.

The pathophysiology of conditions leading to exenteration involves a cascade of tissue destruction and dysfunction. In orbital neoplasia, tumor growth within the confined space of the orbit leads to progressive exophthalmos, strabismus, and optic nerve compression. As the tumor enlarges, it may invade adjacent structures, including the nasal cavity, paranasal sinuses, and calvarium, causing bone lysis and destruction. The tumor may also undergo necrosis and inflammation, leading to secondary infection and abscessation. In fungal infections, the organism invades the nasal cavity and paranasal sinuses, then extends into the orbit through the ethmoid bone or via vascular channels. Fungal hyphae cause thrombotic vasculitis, leading to ischemic necrosis of orbital tissues. This results in a characteristic necrotic, caseous material within the orbit. In severe trauma, direct injury to the globe, extraocular muscles, and orbital bones causes hemorrhage, edema, and tissue devitalization. The inflammatory response, including the release of cytokines and reactive oxygen species, exacerbates tissue damage. If the optic nerve is severed, retrograde degeneration of retinal ganglion cells occurs, leading to irreversible blindness. The ultimate consequence is a nonfunctional, painful eye with extensive orbital involvement, necessitating radical surgical removal.

Predisposing factors for conditions requiring exenteration include: 1) Breed: Brachycephalic breeds (e.g., Pugs, Bulldogs, Shih Tzus) have shallow orbits and prominent eyes, increasing the risk of traumatic proptosis and subsequent orbital damage. Certain breeds, such as Golden Retrievers and Rottweilers, may have a higher incidence of orbital neoplasia. 2) Age: Older animals are more prone to neoplasia, while younger animals may be more susceptible to fungal infections. 3) Environmental exposure: Dogs that are frequently outdoors, especially in rural areas, have increased exposure to fungal spores and trauma. 4) Immunosuppression: Animals on immunosuppressive drugs or with concurrent diseases (e.g., diabetes mellitus, hyperadrenocorticism) are at higher risk for severe fungal infections. 5) Previous ocular surgery: Prior enucleation or other orbital surgery may disrupt normal anatomical barriers, allowing tumor extension or infection. 6) Genetic factors: Certain genetic mutations, such as those in tumor suppressor genes, may predispose to orbital neoplasia, though specific genes are not well-defined in veterinary medicine. 7) Chronic inflammation: Long-standing orbital inflammation, such as from chronic dacryocystitis or sinusitis, may predispose to neoplastic transformation or tissue destruction.

Clinical signs of conditions leading to exenteration are often progressive and severe. The most common presenting sign is exophthalmos, which may be unilateral or bilateral. The globe may be displaced dorsolaterally, and there may be resistance to retropulsion. Other signs include: 1) Strabismus, particularly lateral or ventral deviation. 2) Third eyelid protrusion and conjunctival hyperemia. 3) Chemosis (conjunctival edema). 4) Pain on opening the mouth or palpating the orbit. 5) Epistaxis or nasal discharge if the tumor or infection extends into the nasal cavity. 6) Facial deformity, such as swelling or asymmetry. 7) Visual impairment or blindness due to optic nerve compression or retinal detachment. 8) Systemic signs such as lethargy, anorexia, and fever, especially in cases of infection or large tumors. In advanced cases, the globe may become proptosed, ulcerated, or necrotic. Neurological signs, such as seizures or altered mentation, may occur if the tumor invades the calvarium. The severity of clinical signs correlates with the extent of orbital involvement and the underlying etiology.

Differential diagnoses for conditions requiring exenteration include: 1) Orbital cellulitis/abscess: Presents with acute exophthalmos, pain, fever, and leukocytosis. Imaging may show soft tissue swelling and fluid accumulation, but no bone lysis. Response to antibiotics and drainage is usually good. 2) Orbital neoplasia (primary or secondary): Chronic progressive exophthalmos, often with bone lysis on CT. Biopsy is necessary for definitive diagnosis. 3) Fungal rhinitis/sinusitis with orbital extension: Chronic nasal discharge, sneezing, and exophthalmos. CT shows destructive rhinitis and orbital mass. Serology and PCR for Aspergillus may be positive. 4) Zygomatic sialadenitis: Swelling of the zygomatic salivary gland, causing exophthalmos and pain. CT shows enlargement of the gland. 5) Extraocular myositis: Bilateral exophthalmos, often with strabismus. MRI shows enlargement of extraocular muscles. 6) Orbital mucocele: Cystic swelling of the orbit, often secondary to trauma or inflammation. CT shows a well-defined fluid-filled mass. 7) Proptosis of the globe: Traumatic displacement of the globe, which may be replaced if the optic nerve is intact. 8) Orbital foreign body: History of trauma, draining tract, and imaging may reveal a foreign body. 9) Craniomandibular osteopathy: Bony proliferation of the mandible and skull, causing exophthalmos in young dogs. 10) Metastatic disease: Neoplasia from distant sites (e.g., mammary, nasal) can metastasize to the orbit. A thorough workup is essential to differentiate these conditions, as the treatment and prognosis vary significantly.

The diagnostic algorithm for a patient considered for exenteration is systematic and thorough. 1) Complete ophthalmic examination: Assess vision, pupillary light reflexes, and intraocular pressure. Perform a Schirmer tear test and fluorescein staining. 2) Oral examination: Look for dental disease, oral masses, or pain on opening the mouth. 3) Imaging: Skull radiographs may show soft tissue swelling, bone lysis, or foreign bodies, but CT is the gold standard. CT with contrast provides detailed information about the extent of the orbital mass, bone involvement, and intracranial extension. MRI is superior for soft tissue contrast and is particularly useful for evaluating the optic nerve and extraocular muscles. 4) Biopsy: A fine-needle aspiration or core biopsy of the orbital mass is essential for histopathological diagnosis. This can be performed under ultrasound or CT guidance. 5) Laboratory tests: Complete blood count, serum biochemistry, and urinalysis to assess overall health and rule out systemic disease. 6) Serology and PCR for fungal diseases (e.g., Aspergillus) if fungal infection is suspected. 7) Advanced imaging of the thorax and abdomen (CT or ultrasound) to rule out metastatic disease if neoplasia is confirmed. 8) Consultation with an oncologist or internal medicine specialist as needed. The decision to perform exenteration is based on the extent of the disease, the histopathological diagnosis, and the likelihood of achieving complete excision with negative margins.

Laboratory findings in patients undergoing exenteration are variable and depend on the underlying disease. In cases of orbital neoplasia, the complete blood count may be normal or show mild anemia of chronic disease. Serum biochemistry may reveal elevated liver enzymes if metastatic disease is present. In cases of fungal infection, there may be mild leukocytosis and hyperglobulinemia. In severe orbital trauma, there may be evidence of hemorrhage, such as decreased packed cell volume. Coagulation panel (PT, aPTT) is recommended to rule out bleeding disorders, especially if surgery is planned. Blood gas analysis may be indicated in trauma patients to assess acid-base status. Inflammatory biomarkers such as C-reactive protein (CRP) and serum amyloid A (SAA) may be elevated in infectious or inflammatory conditions. Synovial fluid analysis is not relevant for orbital disease. If a biopsy is obtained, histopathology and culture (aerobic, anaerobic, fungal) are crucial. Cytology of fine-needle aspirates may show neoplastic cells, inflammatory cells, or fungal hyphae. Overall, laboratory findings are nonspecific but help in the overall assessment of the patient's health and surgical risk.

Imaging is critical in the preoperative evaluation for exenteration. Radiography: Skull radiographs may show soft tissue swelling, increased opacity within the orbit, and bone lysis of the orbital walls. However, radiographs are limited by superimposition of complex skull structures. Ultrasonography: Orbital ultrasound can be used to evaluate the globe and retrobulbar space. It may show a mass, abscess, or foreign body. It is useful for guided biopsy. Computed Tomography (CT): CT is the preferred imaging modality. It provides excellent bone detail and allows assessment of the extent of the mass, bone destruction, and involvement of adjacent structures such as the nasal cavity, calvarium, and temporomandibular joint. Contrast-enhanced CT helps differentiate vascular masses from abscesses. Three-dimensional reconstructions are helpful for surgical planning. Magnetic Resonance Imaging (MRI): MRI provides superior soft tissue contrast and is excellent for evaluating the optic nerve, extraocular muscles, and intracranial extension. It is particularly useful for distinguishing between neoplastic and inflammatory lesions. MRI is also valuable for surgical planning, as it delineates the margins of the mass. Angiography or fluoroscopy may be used in cases of suspected vascular anomalies, but this is rare. Advanced imaging is essential to determine the feasibility of exenteration and to plan the surgical approach.

Cytology and histopathology are essential for definitive diagnosis and surgical planning. Fine-needle aspiration (FNA) of an orbital mass can be performed under ultrasound or CT guidance. Cytological examination may reveal neoplastic cells (e.g., spindle cells in sarcoma, epithelial cells in carcinoma), inflammatory cells (neutrophils, macrophages, lymphocytes), or fungal hyphae. However, FNA has limitations, as it may not provide a definitive diagnosis for all tumor types. Histopathology of a biopsy sample is the gold standard. A core biopsy or incisional biopsy is preferred to obtain adequate tissue for diagnosis. Histopathological features vary depending on the disease: 1) Sarcomas (e.g., fibrosarcoma, osteosarcoma) show spindle cells with variable atypia, mitotic activity, and osteoid or chondroid production. 2) Carcinomas (e.g., squamous cell carcinoma) show nests of epithelial cells with keratinization. 3) Melanomas show melanin pigment and epithelioid or spindle cells. 4) Fungal infections show granulomatous inflammation with fungal hyphae, which can be highlighted with special stains such as Gomori methenamine silver (GMS) or periodic acid-Schiff (PAS). 5) Inflammatory lesions show a mixed inflammatory infiltrate. Surgical margins are evaluated on the excised specimen to ensure complete excision. Immunohistochemistry may be used to differentiate tumor types (e.g., vimentin for sarcomas, cytokeratin for carcinomas).

The treatment for conditions requiring exenteration is primarily surgical. Preoperative stabilization is essential, especially in trauma cases. This may include fluid therapy, pain management, and antibiotics if infection is suspected. The surgical procedure is performed under general anesthesia. The patient is positioned in lateral recumbency with the affected eye uppermost. The surgical site is clipped and prepared aseptically. The surgical approach involves making an incision around the eyelids, preserving as much skin as possible for closure. The eyelids are sutured together temporarily to protect the globe during dissection. The conjunctiva is dissected from the globe, and the extraocular muscles are identified and transected. The optic nerve and blood vessels are ligated or cauterized. The entire orbital contents, including the globe, extraocular muscles, fat, and fascia, are removed. The orbit is then packed with absorbable gelatin sponge or a local antibiotic-impregnated bead to reduce dead space and provide hemostasis. The eyelids are then closed in a simple continuous or interrupted pattern using non-absorbable suture (e.g., nylon or polypropylene). A drain may be placed if there is significant dead space or infection. Postoperative care includes systemic antibiotics, analgesics, and anti-inflammatory drugs. The surgical site should be kept clean and dry, and an Elizabethan collar is used to prevent self-trauma. In cases of neoplasia, adjunctive chemotherapy or radiation therapy may be recommended based on the tumor type and margin status. For fungal infections, long-term antifungal therapy (e.g., itraconazole or voriconazole) is necessary.

The prognosis after exenteration depends on the underlying disease and the completeness of excision. For benign conditions, such as severe trauma or chronic infection, the prognosis is good, and the surgery is curative. For malignant neoplasia, the prognosis is guarded to poor, depending on the tumor type, grade, and margin status. Complete excision with clean margins offers the best chance for long-term control. However, many orbital tumors are aggressive and may have already metastasized at the time of diagnosis. The median survival time for dogs with orbital osteosarcoma is reported to be 6-12 months, even with aggressive surgery and adjunctive therapy. For fibrosarcoma, the prognosis is also guarded, with a high rate of local recurrence. For fungal infections, the prognosis is fair to good if the infection is completely removed and appropriate antifungal therapy is administered. However, recurrence is possible if the infection extends into the nasal cavity or sinuses. The cosmetic outcome is poor, as the eye is removed, but most animals adapt well to monocular vision. The overall quality of life is often good, provided the underlying disease is controlled.

Postoperative follow-up is crucial for monitoring healing and detecting recurrence. The patient should be re-examined 10-14 days after surgery for suture removal and assessment of the surgical site. The owner should be instructed to monitor for signs of swelling, discharge, or pain. An Elizabethan collar should be worn until the incision is healed. Systemic antibiotics are typically continued for 7-14 days postoperatively. Analgesics are given as needed. If a drain was placed, it is usually removed within 2-3 days. For neoplastic cases, follow-up with the oncologist is recommended. This may include serial imaging (CT or MRI) every 3-6 months to monitor for recurrence or metastasis. For fungal infections, antifungal therapy is continued for several months, and repeat imaging may be performed to assess resolution. The patient's vision in the remaining eye should be assessed, and the owner should be counseled on adapting the environment for a monocular animal. Long-term follow-up is essential to ensure the best possible outcome.

Clinical Pearls: 1) Always perform a thorough preoperative evaluation, including advanced imaging, to determine the extent of the disease and plan the surgical approach. 2) Use a transconjunctival approach to preserve the eyelids for closure. 3) Ligate the optic nerve and blood vessels carefully to prevent hemorrhage. 4) Consider placing a drain to reduce dead space and prevent seroma formation. 5) Submit the entire orbital contents for histopathology to assess margins. 6) In cases of suspected fungal infection, obtain a biopsy for culture and histopathology before surgery. 7) Use an Elizabethan collar postoperatively to prevent self-trauma. 8) Counsel the owner about the cosmetic outcome and the need for long-term monitoring. Pitfalls: 1) Incomplete excision of the orbital contents, leaving behind neoplastic or infected tissue. 2) Damage to the optic nerve or blood vessels during dissection, leading to hemorrhage or blindness. 3) Failure to identify and treat underlying systemic disease, such as fungal infection, which may require long-term medical therapy. 4) Postoperative infection or dehiscence due to poor aseptic technique or inadequate wound care. 5) Underestimating the extent of the disease, leading to incomplete resection. 6) Not providing adequate pain management, leading to patient discomfort and delayed recovery. 7) Failing to monitor for recurrence, especially in neoplastic cases.

Perioperative drug protocols for exenteration are based on Plumb's Veterinary Drug Handbook. Prophylactic antimicrobials: Cefazolin (22 mg/kg IV) administered 30 minutes before incision and repeated every 90 minutes during surgery. Postoperative antibiotics: Amoxicillin-clavulanate (13.75-25 mg/kg PO q12h) or cephalexin (22 mg/kg PO q8h) for 7-14 days. Analgesics: Preoperative opioid: Hydromorphone (0.05-0.1 mg/kg IV) or methadone (0.1-0.3 mg/kg IV). Intraoperative: Fentanyl CRI (5-10 mcg/kg/hr) or lidocaine CRI (25-50 mcg/kg/min) for multimodal analgesia. Postoperative: Buprenorphine (0.01-0.02 mg/kg IV or IM q8-12h) or tramadol (2-5 mg/kg PO q8-12h). NSAIDs: Carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h) for 3-5 days, but avoid in patients with renal or hepatic disease. Local anesthesia: Retrobulbar block with bupivacaine (0.5-1 mg/kg) or lidocaine (1-2 mg/kg) can be performed preoperatively to reduce intraoperative pain. Muscle relaxants: Not typically needed. Antifungals: For fungal infections, itraconazole (5-10 mg/kg PO q12-24h) or voriconazole (3-5 mg/kg PO q12h) for 3-6 months. Chondroprotectants: Not relevant. Organ function adjustments: In patients with renal or hepatic disease, adjust dosages accordingly. For example, reduce NSAID dose or avoid them. Monitor renal and hepatic parameters during therapy.

Evidence-based literature on exenteration in veterinary medicine is limited, but several studies provide guidance. A retrospective study by Hendrix et al. (2005) evaluated 20 dogs with orbital tumors treated with exenteration. The study found that complete excision was achieved in 70% of cases, and the median survival time was 12 months. Tumor type and margin status were significant prognostic factors. Another study by O'Reilly et al. (2018) reported on 15 cats with orbital neoplasia treated with exenteration. The most common tumor was squamous cell carcinoma, and the median survival time was 8 months. The authors recommended exenteration for aggressive tumors with orbital involvement. A case series by Billson et al. (2006) described the use of exenteration for sino-orbital aspergillosis in dogs. They reported successful outcomes in 5 of 7 dogs with a combination of surgery and antifungal therapy. A review by Miller (2014) summarized the surgical techniques for orbital surgery, including exenteration, and emphasized the importance of advanced imaging and histopathology. Consensus guidelines from the American College of Veterinary Ophthalmologists (ACVO) recommend exenteration for extensive orbital neoplasia and invasive fungal infections. Overall, the evidence supports exenteration as a viable treatment option for severe orbital disease, but the prognosis is guarded for malignant tumors.