Herausforderungen der magnetresonanztomografischen Diagnose der axialen Spondylarthritis

Zusammenfassung

In der Bildgebung der axialen Spondylarthritiden einschliesslich der ankylosierenden Spondylitis steht das konventionelle Röntgenbild der Sakroiliakalgelenke (SIG) an erster Stelle. Da sich pathologische Veränderungen hier jedoch erst spät nachweisen lassen, verzögert sich die Diagnosestellung im Schnitt um 5–9 Jahre. Die fehlende Sensitivität des Röntgenbildes für frühe Krankheitsstadien lässt also eine diagnostische Lücke entstehen, welche auch den Therapiebeginn erheblich verzögern kann. Mit der Magnetresonanztomografie (MRT) der SIG steht uns eine moderne, sehr sensitive Modalität zur Erkennung der frühen Spondylarthritis (SpA) zur Verfügung, welche diese Lücke schließen kann. Die heute flächendeckende Verfügbarkeit geeigneter MRT-Geräte und die immer genauere Klassifikation der SIG-Veränderungen machen sie zu einer Untersuchungsmethode, welche nicht mehr den großen Krankenhäusern vorbehalten ist, sondern überall im klinischen Alltag eingesetzt werden kann und sollte. Essenziell für die Bildinterpretation ist die Kenntnis der in der MRT sichtbaren Pathologien, welche in aktive und strukturelle Veränderungen eingeteilt werden. Zu den aktiven Veränderungen zählen paraartikuläre Osteitiden, Synovitiden, Kapsulitiden und Enthesitiden; zu den chronischen Veränderungen Erosionen, subchondrale Sklerosierungen, transartikuläre Knochenbrücken und periartikuläre Verfettungen. Sie lassen sich durch ihr jeweils typisches Signalverhalten und ihre Lage gut charakterisieren. Zusätzlich ist das Wissen über mögliche anatomischen Varianten und Differenzialdiagnosen relevant – in unklaren Fällen kann eine ergänzende computertomoprafische Bildgebung hilfreich sein. Die aktuelle Diskussion neuer Konzepte (wie bspw. das „Backfill“ in den SIG) zeigt, dass die diagnostischen Möglichkeiten auch hier in Zukunft noch vielfältiger werden. Eine interdisziplinäre Zusammenarbeit von Rheumatologen und Radiologen mit optimaler Ausschöpfung dieser „frühen“ diagnostischen und therapeutischen Möglichkeiten trägt zu einer Verbesserung der Patientenversorgung bei.

Abstract

Conventional radiography of the sacroiliac joints (SIJs) remains the first-line modality in the imaging diagnosis of axial spondyloarthritides including ankylosing spondylitis. However, radiographic SIJ changes occur late in the evolution of disease, delaying the radiographic diagnosis by an average of 5–9 years. Therefore, the lack of sensitivity of radiographs to early disease is a diagnostic gap that can considerably delay the initiation of appropriate treatment. This gap may be closed by magnetic resonance imaging (MRI) of the SIJs – a highly sensitive, state-of-the-art imaging modality for the detection of early spondyloarthritis (SpA). Suitable MRI systems are now widely available, and the classification of SIJ changes is becoming more and more accurate. Therefore, MRI can and should be used routinely everywhere today and is no longer confined to large hospitals. It is essential for radiologists interpreting the MRI findings to be familiar with the spectrum of abnormalities, which are subdivided into active disease processes and structural lesions. Active disease changes include para-articular osteitis, synovitis, capsulitis, and enthesitis; chronic abnormalities include erosions, subchondral sclerosis, transarticular bone bridging, and periarticular fatty lesions. Structural lesions have typical signal intensities and are found in typical locations, allowing good characterisation of these lesions. Moreover, knowledge of possible anatomic variants and differential diagnoses is relevant. If MRI is inconclusive, supplementary computed tomography may be helpful. The current discussion of new concepts (e. g. backfill of erosions) indicates that the spectrum of diagnostic options will expand further in the future. Interdisciplinary cooperation of rheumatologists and radiologists with optimal use of early diagnostic and therapeutic options will improve patient management.

Schlüsselwörter

MRT - Sakroiliitis - Spondyloarthritis - Osteitis condensans

Key words

MRI - sacroiliitis - spondyloarthritis - osteitis condensans

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