Corticated and non-corticated borders

A corticated border is a thin radiopaque line running around the edge of a radiolucent lesion on a radiograph. Cysts that arise within bone typically have one [1]. A non-corticated border lacks that line: the edge may still be sharp, or it may fade gradually into the surrounding bone, which is called an ill-defined border [2, 4].

Synonyms: corticated margin; non-corticated border

What is a corticated border on a radiograph?

Find the edge of the radiolucency and follow it all the way round. If a thin radiopaque line separates the dark lesion from the normal bone around it, the border is corticated.

Cysts that originate within bone typically show exactly this: a well-defined corticated margin, often seen as a thin radiopaque line [1]. Whether you're reading a periapical radiograph or a panoramic, the question you're asking is the same: what is the edge made of?

How does a corticated border differ from a non-corticated or ill-defined one?

Ask two things of any edge. Is it sharp, or does it fade? And if it's sharp, is there a radiopaque line along it, and how thick is that line?

Two words get used loosely here. Well-defined describes how sharp the edge is. Corticated describes the line along it. A lesion can be well-defined without being corticated, and the difference can matter. One eosinophilic granuloma in the anterior mandible was first diagnosed as a radicular cyst because it was an ovoid radiolucency with a well-defined border. On careful reading, its border was non-corticated, and that was one of the features that pointed away from a cyst [2].

What it's confused with

What does the border tell you about how a lesion is behaving?

The edge records how the bone around a lesion responded to it. In bone-tumour radiology, the reaction of the local bone depends on how fast the lesion grows, so growth rate can be estimated from a single radiograph [9]. A narrow zone of transition gives a sharp, well-defined border and is a sign of slow growth. A broad zone of transition gives an ill-defined border and is a sign of aggressive growth [4]. The presence of a sclerotic rim is one of the four descriptors in the Lodwick system for grading the growth rate of lytic bone tumours [9].

Those rules come from skeletal radiology, not from studies of the jaws. The jaw literature states the same tendency: lesions with well-defined margins are generally considered benign, and ill-defined margins tend to suggest more aggressive, inflammatory or neoplastic processes [1].

Jaw-specific follow-up data are thin. One retrospective study followed 85 untreated cystic and cyst-like jaw lesions on two panoramic radiographs taken 1 to 13 years apart. Only 26 of the lesions had a histological diagnosis [1].

• Lesions with no corticated margin at the start grew by a larger percentage than lesions that were corticated [1].
• Cortication appeared over time. Of the 44 lesions that were non-corticated on the first radiograph, 33 were corticated on the second. Radicular cysts followed this pattern: 8 of the 9 that started without cortication gained it [1].
• Cortication didn't mean growth had stopped. The three odontogenic keratocysts had well-defined corticated borders on both radiographs and still enlarged [1].

The authors draw no causal conclusion from these patterns, and they state that their data can't settle the clinical significance of corticated versus non-corticated borders [1]. Read the border as one clue to behaviour, not a verdict.

When does the border appearance mislead?

A sharp edge doesn't make a lesion benign. Beyond the eosinophilic granuloma above [2], malignant lesions can have sharp edges. In a series of 66 osteosarcomas of the jaws, 22% had defined but non-corticated borders and 78% had diffuse borders [10]. A systematic review of 50 cases of solitary plasmacytoma of the jaw found it commonly presents as a multilocular radiolucency with well-defined borders [11]. A skeletal bone-tumour teaching reference adds that in patients over 30, and particularly over 40, metastasis or plasmacytoma has to be considered even when the radiographic features look benign [4].

A fuzzy edge doesn't make a lesion malignant. Infection and eosinophilic granuloma are benign, but their aggressive biological behaviour can make them mimic a malignant bone tumour [4].

Multiple myeloma produces radiolucencies called punched-out lesions. At one Japanese centre, 18 of 98 patients with symptomatic myeloma (18.4%) had them in the mandible [12]. In three dimensions the picture is less tidy: on CBCT, myeloma lesions of the jaws tend to be poorly defined, and one series of 33 patients found no well-defined lesions [5]. A scoping review found ill-defined margins with irregular contours described in more studies (10) than punched-out lesions (5) [13].

Normal anatomy has edges too. An enlarged maxillary sinus with a prominent alveolar recess can mimic a periapical cyst [6, 7]. A Stafne bone cavity can present as a well-defined periapical radiolucency, and on CBCT it turns out to be a corticated, scooped-out defect on the lingual surface of the mandible [8]. In the reported cases, three-dimensional imaging (CT or CBCT) settled the question [7, 8]. More of these look-alikes are covered in normal structures mistaken for pathology.

A corticated or sclerotic edge isn't unique to cysts. In a series of 118 patients with osseous (cemento-osseous) dysplasia, 108 (91.5%) had lesions with well-defined, sclerotic or corticated margins, surrounded by a radiolucent border [14].

The projection can change the edge. On panoramic radiographs, cortication can look different because of projection, unequal magnification, geometric distortion and patient positioning, not only because of biology [1]. In the follow-up study above, agreement between the two radiographs on border cortication was weak [1]. Before you read a change in the border as a change in the lesion, ask whether it's a change in the image. It's the same discipline as telling radiographic artifact from pathology.