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Sebaceous gland carcinoma (SGC) of the eyelid is usually considered a rare tumour (1–5% of all cutaneous malignancies in the USA), but higher incidence rates have been seen in Asia (28–60%). It has a tendency for intraepithelial spread, as well as regional and distant metastases. Early diagnosis and timely management can help reduce morbidity and mortality. In the eyelids, it may arise from meibomian glands (most common), glands of Zeis or sebaceous glands associated with the caruncle. It is two to three times more common in the upper lids due to the higher number of meibomian glands. Any unilateral blepharoconjunctivitis with loss of eyelashes and thickening of lid margin that fails to respond to treatment should be biopsied, and so should an atypical or recurrent chalazion.

Orbital cellulitis refers to the infection of the soft tissues of the orbit. It is characterized by acute onset of fever and constitutional symptoms associated with lid swelling, conjunctival chemosis, proptosis and limitation of eye movements. In a severe case, it may be associated with visual loss. In the overwhelming majority (90%) of cases, the source of infection is the paranasal sinuses. Occasionally, an infection in the eyelid or lacrimal sac can extend posteriorly, resulting in orbital cellulitis. An external penetrating wound or a retained orbital foreign body may also be responsible for the cellulitis. In a rare event, an endogenous infective embolus can lodge in the orbital tissues causing orbital cellulitis. Occasionally other pathologies may mimic orbital cellulitis requiring radiological and histopathological confirmation.

Computed tomography (CT) scan was introduced in clinical practice in 1971 with single axial slice at a time scanning capability. This has progressively evolved into current modern CT scanners which perform volumetric imaging, with retrospectively reconstructing images in different planes and thicknesses providing high-resolution soft tissue and bone images in short scan durations.

Vascular lesions are classified into tumours and malformations, and malformations are further classified into high-flow and low-flow lesions depending on the haemodynamic characteristics, and there can be combinations of various lesions. The classification of vascular lesions are detailed in the ISSVA (International Society for the Study of Vascular Anomalies). Distensible venous malformation (Common venous malformation [Common VM]), previously known as varices, is the most common type of vascular malformation in the orbit and periorbital region. It is mostly sporadic, but in about 1–2% of cases, it can be familial. It occurs at the venous end of the vascular system and communicates with the venous circulation, thereby causing an increase in size with Valsalva manoeuvre. Common VM is usually present at birth and enlarges with hormonal changes during adolescence and adulthood. Occasionally, there is sudden expansion due to bleeding.

The term orbital pseudotumour was first coined in 1905 to describe an idiopathic condition that produced a mass effect and inflammatory features in the orbit, after exclusion of infection and malignancy. It is now increasingly replaced by the terms “orbital inflammatory disease” (OID) or “idiopathic orbital inflammation”, as its wide spectrum of clinical presentation is increasingly recognized. Orbital inflammatory disease can be divided into specific and non-specific orbital inflammations. Specific orbital inflammatory disorders include idiopathic sclerosing inflammation, granulomatous disorders, transitional lesions (e.g. Sjogren’s syndrome, Kimura disease), vasculitic disorders (e.g. granulomatosis with polyangiitis [Wegener’s granulomatosis]), and others. Non-specific inflammatory cases are a diagnosis of exclusion, and can be classified according to their location in the orbit: anterior, diffuse, apical, myositic, and lacrimal.

Pleomorphic adenomas (also known as benign mixed tumours) of the lacrimal gland arise from epithelial and mesenchymal elements such as ducts, myoepithelial components and stroma. Up to 50% of lacrimal gland tumours are epithelial, and a good number of them are pleomorphic adenomas. They typically occur in the 2nd to 5th decades of life, with no gender predilection. Clinically, they present as mass lesions, manifesting as slowly progressive, painless proptosis. Complete surgical removal along with pseudocapsule and a rim of normal tissue is the treatment of choice.

A mucocoele is a chronic, cystic lesion of the paranasal sinuses, lined by pseudostratified or low columnar epithelium. There is background inflammation, with the cyst filled with mucus, exerting pressure on the boundaries of the sinus due to obstruction of the sinus ostium. The obstruction is caused by congenital anomalies, allergy, infection, trauma, neoplasms and sinus surgery. Surgery is necessary for a complete cure. The ultimate goal of surgical intervention involves in re-establishing the sinus drainage and obliteration of the cavity with complete resection of the sinus mucosal lining.

Thyroid eye disease (TED), also known as thyroid-associated orbitopathy (TAO), is a chronic inflammation of the orbital tissues. It is an autoimmune process that mostly affects patients with Graves’ disease, but it can also affect patients with other autoimmune disorders of the thyroid. Middle-aged women are more prone; the gender ratio between women and men is 4:1. When males develop TED, it tends to be more severe. The disease is also severe in smokers. The diagnosis is often made with clinical signs along with the biochemical changes of thyroid hormone in the blood. Occasionally, imaging is necessary to differentiate it from other causes of muscle enlargement and space-occupying lesions of the orbit. Very rarely, a biopsy of the muscle is necessary to rule out other serious causes of muscle enlargement.

T-cell lymphomas of the ocular adnexa are extremely rare and when present may be a manifestation of known preexisting systemic disease. They arise primarily from the paranasal sinuses, more commonly in East Asians. While B-cell lymphomas are usually well recognized and more easily treated, T-cell lymphomas often carry a guarded prognosis.

Fibro-osseous lesions are a poorly defined group of lesions that affect the jaw and the craniofacial bones. The World Health Organization (WHO) classified these lesions in 2005, which include ossifying fibroma, fibrous dysplasia, and osseous dysplasia (Paget’s disease), in addition to reactive bone lesions. The diagnosis and management is challenging, often requiring multidisciplinary approach.