A lump or fullness behind the eye: orbital tumours, and what imaging and biopsy decide

A fullness behind one eye, an eye that sits a little further forward than the other, or a change in how the eye moves: these are the ways a growth in the eye socket can announce itself. Not every push is a tumour. Thyroid eye disease, inflammation, infection and injury are more familiar causes, and I cover them in the page on bulging eyes in adults. This article is about the growths: what they are, which symptoms should lead to a scan, what the scan can and cannot settle, and why a biopsy so often makes the final decision.

What is an orbital tumour, and which ones occur in adults?

An orbital tumour is an abnormal growth inside the orbit, the bony socket that holds the eye, its muscles, nerves, fat and tear gland. It can be benign or malignant, and it can start in the orbit or spread to it from elsewhere. The MSD Manual lists the common benign tumours in adults as meningiomas, mucoceles and cavernous venous malformations, and calls the cavernous venous malformation the most common benign orbital tumour. A mucocele is a fluid-filled sac, often arising from a sinus. A pleomorphic adenoma is a benign growth of the lacrimal gland, the tear gland that sits at the upper outer corner of the socket.

The malignant ones named by the same source are lymphoma, squamous cell carcinoma and metastatic disease, meaning cancer that has travelled from another organ. Adenoid cystic carcinoma of the lacrimal gland is less common and is described as aggressive. Lymphoma, a cancer of the lymphocytes that make up part of the immune system, is the most frequent malignant orbital tumour in adults, and I come back to it below.

Several things that are not tumours can look the same on a scan. Orbital inflammation and vascular malformations are described in my guide to orbital conditions. A smooth cyst at the upper outer corner of the lid is a separate problem, and the article on orbital dermoid cysts covers it.

Which symptoms behind the eye should lead to imaging?

An eye that is being pushed forward, or sideways, up or down. Laplant and Cockerham, in a review of primary malignant orbital tumours, name progressive proptosis, the medical word for a forward-pushed eye, as the main symptom. The MSD Manual adds displacement of the eyeball upward or downward, pain, double vision and loss of vision. A change like this that is new, affects one eye and does not settle is a reason to be examined, and the examination decides whether a scan is needed.

Two cautions. The first is that some tumours cause surprisingly little. The MSD Manual says orbital lymphoma may cause minimal symptoms despite significant findings on imaging, and that it can affect both sides. A painless fullness is therefore not reassuring by itself. The second is that the symptoms are not specific: thyroid eye disease, inflammation and infection produce much the same list. The examination, the history and the pattern over weeks are what separate them, and a scan is requested to answer a question the examination cannot. I set out how that choice is made in the page on which scan to have, so I will not repeat it here.

Loss of vision, double vision, or an eye that is painful or being pushed forward quickly should not wait for a routine appointment.

What do CT and MRI actually decide?

They decide where the mass is, how big it is, what it touches, and whether bone or the optic nerve is involved. They rarely decide what it is. Laplant and Cockerham state that CT is useful for the bony structures, while MRI is preferred for soft tissue and for tumours at the apex, the narrow back of the socket where the optic nerve enters. They also note that well-circumscribed lesions tend to be benign and that malignant lesions are more often irregular and poorly defined. That is a tendency, not a rule.

The limits are worth stating plainly, and a study I co-authored shows them clearly. In a ten-year series from one UK tertiary centre, 88 consecutive orbital biopsies were reviewed: 36 turned out to be lymphoma and 52 inflammatory disease. Before the biopsy, the radiological assessment had a sensitivity of 61.1% and a specificity of 88.5%. Put simply, when the scan raised suspicion of lymphoma it was usually right, but a scan that did not raise suspicion could not rule it out. Twelve lymphoma cases, a third of them, were missed by both the clinical and the radiological assessment. Almost every lymphoma in the series occurred in someone aged 55 or over, which fits the pattern Laplant and Cockerham describe in older adults.

That is one retrospective study from one centre. It shows what happened there, not what will happen to any one person. The authors' conclusion was that pre-biopsy assessment can raise suspicion when it is positive but cannot safely exclude lymphoma when it is negative.

When is a biopsy needed?

When the treatment depends on knowing what the tissue is and the scan cannot say. The MSD Manual puts it this way: the diagnosis is suspected from the history, examination and imaging, but confirmation often ultimately requires a biopsy. A biopsy takes tissue for a pathologist to examine under the microscope, usually with extra laboratory tests that name the exact cell type.

Laplant and Cockerham describe two kinds. An incisional biopsy takes part of the lesion, and an excisional biopsy removes all of it. The choice depends on the lesion and on how close it lies to structures that matter, such as the optic nerve and the eye muscles. Some benign growths, including the cavernous venous malformation and the tear gland pleomorphic adenoma, are managed by excision according to the MSD Manual, so the operation itself supplies the tissue.

The reason not to guess is that the treatments diverge. Inflammation and lymphoma can look alike and are treated in completely different ways, which is why my orbital conditions guide calls biopsy the step that decides. A case report on an inflammatory-looking orbit that hid lymphoma, published in Cureus, makes the same point and recommends a tissue biopsy by a minimally invasive route when the cause of inflammation is being sought. Surgery near the eye carries its own risks, which the surgeon explains beforehand, and that is why the scan comes first and the biopsy is planned.

What is ocular adnexal lymphoma?

It is a lymphoma arising in the tissues around the eyeball, the adnexa, which include the orbit. Reviews describe the commonest type as extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue, usually shortened to MALT lymphoma. In a series of 84 primary patients classified under the World Health Organization system, MALT lymphoma made up 57% and follicular lymphoma 18%.

The MSD Manual describes orbital lymphomas as typically B-cell and characteristically low grade, a term that means the cancer tends to behave slowly. Laplant and Cockerham report that lymphoproliferative lesions account for up to 20% of orbital masses and that lymphoma makes up 70 to 90% of them in adults older than 60. For that reason an older adult with a slowly growing orbital mass is assessed with lymphoma in mind, without assuming it.

What happens after the biopsy result?

The pathology report sets the next step, and for lymphoma that step moves beyond the eye surgeon. The Cureus report notes that an estimated 30 to 50% of patients with orbital lymphoma of all types present with, or go on to develop, disease elsewhere in the body. Staging is therefore done: a body CT scan, and in some cases a bone marrow biopsy. Treatment is decided with a haematologist and a radiation oncologist, not by the orbital surgeon alone.

What follows depends on the type. For low-grade lymphoma, the few mostly retrospective studies cited in the Cureus report suggest that radiotherapy alone may be enough, while aggressive lymphoma is treated with chemotherapy with or without radiotherapy. The MSD Manual also names the antibody rituximab. A radiation oncology series of ocular adnexal lymphoma found that some people with early-stage MALT lymphoma later had a relapse elsewhere, which is why long-term follow-up matters even after good local control.

If the biopsy shows a benign growth, the discussion becomes whether to remove it, which depends on where it sits and what it is doing to vision, comfort and the position of the eye. My part is the orbit: reaching the tissue safely, protecting sight and handing the result to the right team. If you have noticed a lump or fullness behind one eye, see an ophthalmologist, and bring any earlier scans and reports. For the wider map, see the orbit and thyroid eye disease section and my hub article on why eyes look tired.