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OP10.5 | Enucleation, Evisceration and Exenteration Indications — SDL Guide (Part 2)

Enucleation: Indications and the Sympathetic Ophthalmia Prevention Rule

Enucleation removes the entire globe and is the procedure of choice whenever the globe itself must be completely removed — whether because it harbours a malignancy, because it is a source of sympathetic ophthalmia risk, or because the eye is so severely disrupted that it cannot be reconstructed. The oncological rationale for enucleation over evisceration in tumour cases is fundamental and must be understood, not merely memorised. Intraocular tumours — particularly retinoblastoma and choroidal melanoma — can spread beyond the globe through natural pathways: along the optic nerve sheath into the subarachnoid space (optic nerve extension of retinoblastoma); through emissary canals in the sclera (tiny channels through which vortex veins and ciliary vessels pass) into the orbital soft tissue; and through the choroid into the uveal vasculature. Evisceration removes only the intraocular contents and leaves the scleral shell — with all its emissary canals — intact in the orbit. If a retinoblastoma is present, viable tumour cells may have already penetrated scleral emissary canals; leaving the sclera means leaving those cells, and the warm, vascular orbital environment is an excellent culture medium for tumour growth and local spread. Enucleation removes the entire globe including the sclera and the anterior segment of the optic nerve, ensuring that no viable tumour tissue remains. Histopathological examination of the enucleated specimen then determines the surgical and optic nerve margin status, which guides the decision on adjuvant chemotherapy or radiotherapy.

Indications for enucleation:
1. Intraocular malignancy — retinoblastoma: In unilateral advanced retinoblastoma (IIRC Group D or E), where there is no functional vision and the tumour fills the vitreous cavity or has caused neovascular glaucoma, enucleation is the primary treatment. It provides histopathological confirmation of the diagnosis and extent, guides adjuvant chemotherapy decisions, and achieves cure for confined disease. Evisceration is absolutely contraindicated in retinoblastoma (and in any suspected intraocular tumour) because scleral penetration or emissary spread could seed the orbit.
2. Choroidal melanoma: Large melanomas (>10 mm height or >16 mm diameter) where vision-sparing treatments (brachytherapy, charged-particle radiotherapy) are not feasible or have failed.
3. Blind painful eye where tumour cannot be excluded: When a definitive preoperative diagnosis cannot be made and tumour must be excluded histologically, enucleation provides the specimen.
4. Prevention of sympathetic ophthalmia: After a severe penetrating or perforating injury to one eye that leaves the eye blind and disorganised, enucleation of the injured (exciting) eye within 10–14 days prevents the development of sympathetic ophthalmia in the fellow (sympathising) eye. Sympathetic ophthalmia is a bilateral granulomatous panuveitis that occurs weeks to months after uveal tissue is exposed to the systemic immune system through a penetrating wound. Once sympathetic ophthalmia has developed in the sympathising eye, enucleation of the exciting eye no longer cures it (though it may reduce the antigen load) and systemic immunosuppression is required.
5. Severely traumatised globe where reconstruction is futile and the risk of sympathetic ophthalmia is present.
6. Absolute glaucoma (blind eye with intractable pain from raised IOP) that has failed all medical and surgical IOP-lowering measures — though some surgeons prefer evisceration in this setting if tumour is excluded.

Exenteration: Indications for Orbital Malignancy and Mucormycosis

Exenteration is the most radical of the three procedures and is reserved for conditions where the disease has spread beyond the globe to involve the orbital soft tissues or where the orbital contents are the primary site of disease. The decision to perform exenteration must balance oncological effectiveness against the profound functional and cosmetic consequences of losing the entire orbit's contents. To appreciate why exenteration is sometimes the only viable option, consider the anatomy of orbital malignancy spread: the orbit is a bony cone with openings at the apex (optic canal, superior orbital fissure) connecting directly to the intracranial compartment, and laterally it is bounded only by thin bony walls separating it from the temporal fossa and maxillary sinus. A malignant tumour infiltrating the orbital fat has access to all of these pathways. Perineural tumours (adenoid cystic carcinoma of the lacrimal gland) travel along the frontal, lacrimal, and nasociliary nerve branches directly toward the trigeminal ganglion and the intracranial compartment — no amount of local resection will achieve clear margins if the perineural spread is not addressed radically. Mucormycosis invades blood vessel walls (angioinvasion), causing thrombosis of the ophthalmic artery and its branches and creating ischaemic necrosis of all orbital tissues while simultaneously tracking along the vessel walls toward the cavernous sinus and brain. In both situations, the orbital contents are already non-viable or tumour-infiltrated, and their removal — though devastating in terms of appearance — removes the source of ongoing spread and can be genuinely life-saving. Subtotal or piecemeal resections in these settings carry a very high rate of local recurrence and intracranial extension, which is why the radical approach is preferred despite its consequences.

Indications for exenteration — malignancy:
1. Squamous cell carcinoma (SCCa) of the eyelid or periocular skin with deep orbital invasion: When SCCa has penetrated through the tarsal plate into the orbital fat or around the globe, complete resection requires removing the orbital contents. Periorbital SCCa in patients with long-standing xeroderma pigmentosum or immunosuppression may require exenteration.
2. Adenoid cystic carcinoma of the lacrimal gland: A perineural-spreading malignancy with a strong tendency for intracranial extension; exenteration combined with removal of perineural tissue along the facial nerve branches offers the best locoregional control.
3. Conjunctival melanoma with orbital invasion: Melanoma originating in the conjunctiva that has invaded the orbit.
4. Sebaceous gland carcinoma (arising from Meibomian glands) with orbital spread: A particularly aggressive tumour with skip lesions and pagetoid spread; may require exenteration in advanced cases.
5. Rhabdomyosarcoma: The commonest primary orbital malignancy in children; usually treated with chemotherapy + radiotherapy, but exenteration may be required for chemotherapy-resistant disease.

Exenteration for orbital mucormycosis (life-saving emergency):
Mucormycosis is a rapidly invasive fungal infection caused by Mucorales species (Rhizopus, Mucor, Cunninghamella). It occurs almost exclusively in immunocompromised individuals — most classically, poorly controlled diabetes mellitus (the fungal hyphae thrive in the acidotic, hyperglycaemic, ketotic environment), but also patients on corticosteroids, haematological malignancy, solid organ transplantation, or COVID-19-associated mucormycosis (CAMO). The organism invades blood vessels (angioinvasion), causing thrombosis and tissue necrosis, and spreads rapidly along vascular channels from the rhinosinuses into the orbit and thence intracranially. Rhino-orbital-cerebral mucormycosis is the most common clinical syndrome. Once orbital invasion is confirmed and antifungal therapy (IV liposomal amphotericin B) is not arresting the spread, emergency orbital exenteration is performed to remove all infected tissue and provide a physical barrier to intracranial spread. The mortality from untreated rhino-orbital-cerebral mucormycosis approaches 100%; even with exenteration and antifungal therapy, mortality remains significant (30–50%). Control of the underlying diabetes (insulin infusion, normoglycaemia) is an essential parallel intervention.

Examination and Investigation Before Surgery

Before proceeding with any of these three procedures, a structured investigation pathway establishes the diagnosis, stage, and surgical plan. The pre-operative workup serves three simultaneous purposes: confirming the indication for surgery, excluding a contraindication (most critically, excluding intraocular tumour before proceeding with evisceration), and planning the operative approach and reconstructive strategy. The most important single investigation before any evisceration is B-scan ultrasound of the eye — a five-minute, non-invasive, readily available test that images intraocular structures through opaque media and detects any solid intraocular mass. Skipping this step has led to catastrophic errors: a phthisical eye that is blind, soft, and opaque may contain a choroidal melanoma that has outgrown its blood supply and presents clinically as a 'burned-out' eye with no visible tumour features on slit-lamp examination. Without B-scan, the surgeon proceeds with evisceration, leaves viable melanoma in the scleral shell, and seeds the orbit — converting a potentially curable enucleation case into an orbital and potentially metastatic recurrence. For retinoblastoma, MRI of the orbit and brain is the key pre-operative investigation — it identifies optic nerve involvement (which changes surgical approach and prognosis) and detects trilateral retinoblastoma (pineal gland involvement). For exenteration cases, CT and MRI together delineate bony erosion and soft tissue extent to guide the reconstructive plan.

Ophthalmic examination:
- Visual acuity (including light perception — a seeing eye is never removed unless there is an overriding oncological reason).
- Pupil reactions and extraocular movements.
- Slit-lamp examination: anterior segment for tumour extension, corneal and scleral involvement.
- Fundus examination under mydriasis: identify the intraocular lesion.

Imaging:
- Ultrasound B-scan: The most important initial investigation before any evisceration or enucleation. In a phthisical eye with opaque media, B-scan confirms the absence of an intraocular solid mass (which would contraindicate evisceration). In retinoblastoma, B-scan shows a dense echogenic mass with acoustic shadowing (calcium deposits — pathognomonic of retinoblastoma). In choroidal melanoma, B-scan shows the acoustic hollowness of the lesion.
- CT orbit (with and without contrast): Delineates bony orbital walls and detects calcification (retinoblastoma). Critical for exenteration planning to assess bony erosion.
- MRI orbit (with fat suppression + gadolinium): Superior soft-tissue resolution; detects extraocular extension of tumour, orbital fat infiltration, optic nerve sheath involvement, and perineural spread. Standard preoperative investigation before enucleation for retinoblastoma and before exenteration.
- CT chest + abdomen (for systemic staging of melanoma and other malignancies before surgery).

Biopsy: In orbital tumours requiring exenteration, a tissue diagnosis by incisional biopsy or fine-needle aspiration cytology (FNAC) should be obtained before proceeding — except in cases of aggressive mucormycosis where surgical speed is more important and the clinical diagnosis is clear. For retinoblastoma, biopsy of the intraocular tumour is CONTRAINDICATED (risk of orbital seeding); the diagnosis is clinical + imaging.

Systemic assessment: Full blood count, coagulation screen, metabolic panel (renal function, glucose — particularly important in diabetic mucormycosis patients), ECG, and anaesthetic fitness.