Although lumbar spondylolysis is a widely known and easily recognizable condition in its typical presentation, there are some less well-known forms that may occasionally be challenging and/or demand special attention on imaging. Examples include: acute and/or incomplete lesions; unilateral defects; lesions at unusual levels (cervical, upper lumbar, and multi-level spondylolyses); iatrogenic lesions; non-isthmic spondylolysis; and spondylolysis related to underlying diseases. In addition to their atypical, uncommon or confusing imaging presentations, these forms of spondylolysis are far rarer than the classic type and have been described, to a great extent, in the surgical literature, thus reducing the awareness of radiologists about them and raising the potential for misdiagnosis and inadequate treatment. In this review the authors address these special manifestations of spondylolysis, stressing the more important features to be considered in the differential diagnosis and the impact of a precise diagnosis of spondylolysis on the patient's care.

-Cavernous angiomas (cavernomas) of the cavernous sinus are uncommon, with only scattered reports in literature. Unlike their parenchymatous counterparts, they are intensely enhancing para-sellar masses, iso/hypointense in T1-and hyperintense in T2-weighted images. Differential diagnosis with parasellar meningiomas and schwannomas can be difficult. We report three cases of this condition, describing findings of diffusion-weighted imaging in this kind of lesion for the first time in literature.KEY WORDS: cavernous angioma, cavernous sinus, magnetic resonance imaging, computed tomography, angiography.Angioma cavernoso do seio cavernoso: achados aos exames de imagem RESUMO -Angiomas cavernosos (cavernomas) do seio cavernoso são lesões incomuns, com poucos relatos na literatura especializada. Ao contrário dos cavernomas parenquimatosos, são massas para-selares intensamente captantes, isointensas a hipointensas em T1 e hiperintensas em T2 nas imagens de ressonância magnética. O diagnóstico diferencial com meningiomas e schwannomas para-selares pode ser difícil. Relatamos os achados de imagem de três casos desta entidade, descrevendo os achados da ressonância magné-tica ponderada em difusão neste tipo de lesão pela primeira vez na literatura. PALAVRAS-CHAVE: angioma cavernoso, seio cavernoso, ressonância magnética, tomografia computadorizada, arteriografia.Cavernous angioma of the cavernous sinus is an extremely rare condition, and its differential diagnosis with tumors, namely para-sellar meningiomas and schwannomas, is often difficult. They are richly vascularized lesions, made up of a network of dilated, thin-walled vessels, and are responsible for less than one percent of all intracranial masses. The advent of magnetic resonance imaging (MRI) raised new diagnostic perspectives for this condition as we report in the study. METHODThis study was approved by the committee of Ethics of Clinica Radiologia Vila Rica, Brasilia DF, Brazil.Three female patients, with 42-years-old (patient 1), 45-years-old (patient 2) and 37-years-old (patient 3), are, respectively, presented with complaints of right-sided cranial nerves deficits (III nerve [patients 2 and 3], V1 nerve [patient 2] and VI nerve [patients 1 and 2]) and headaches. All of them underwent magnetic resonance imaging and cerebral digital subtraction angiography (DSA). Patients 2 and 3 were also submitted to computed tomography (CT). In all patients, MRI revealed well-delimited right para-sellar lesions, uniformly isointense in T1-weighted images and hyperintense in T2-, T2-and FLAIRweighted images, brightly enhancing after intra-vascular infusion of gadolinium. Diffusion-weighted sequence, performed in patient 3, revealed an isointense mass.

The so-called "crowned dens" is a peculiar manifestation of calcium crystal deposition diseases, either caused by calcium pyrophosphate dihydrate or caused by calcium hydroxiapatite crystals, characterized by the presence of calcific deposits around the odontoid, often showing a crown-like configuration on imaging. It has protean clinical and radiological pictures, and care should be taken to avoid misinterpretation and diagnostic errors. Although asymptomatic in many patients, this entity may present as a predominantly algic or febrile condition, and in some cases, signs of compression of the spinal cord may be the major complaint. The detection of calcifications in the periodontoid tissues is the key to the diagnosis, erosive osseous changes, and variably calcified soft-tissue masses being occasionally associated. Computed tomography is the most important imaging study to be performed in this setting.