Knee MRI: Vascular Pathology

Vascular complications after a multiligament knee reconstruction: A case report highlighting the role of preoperative imaging

Vascular injuries are serious complications of multiligament knee injuries and can result in catastrophic outcomes. These injuries can range from intimal flaps with no compromise of the distal perfusion to a complete occlusion or transection requiring emergent vascular intervention. Several diagnostic tests, including the measurement of the ankle-brachial index (ABI), conventional angiography, and computed tomography angiography (CTA), are commonly used as diagnostic tools to identify vascular injuries in the context of a multiligament knee injury. In this report, the authors discuss the case of a patient with a normal ABI and palpable distal pulses on physical examination who developed limb ischemia after a multiligament knee reconstruction under tourniquet. The patient underwent emergent embolectomy and had a favorable postoperative outcome. During vascular exploration, there was no evidence of injury to the popliteal artery. The two working diagnoses were that either the patient had an intimal flap complicated by the development of a thrombus during surgery or that the initial vascular injury was not detected by ABI and clinical examination. Therefore, intimal flaps in multiligament knee injuries can lead to limb threatening ischemia in the context of reconstructive knee surgery and are likely underdiagnosed with ABI assessment. The utilization of preoperative CTA may help identify these injuries in patients indicated for reconstructive surgeries.

Detecting Small Anatomical Structures in 3D Knee MRI Segmentation by Fully Convolutional Networks

Accurately identifying the pixels of small organs or lesions from magnetic resonance imaging (MRI) has a critical impact on clinical diagnosis. U-net is the most well-known and commonly used neural network for image segmentation. However, the small anatomical structures in medical images cannot be well recognised by U-net. This paper explores the performance of the U-net architectures in knee MRI segmentation to find a relative structure that can obtain high accuracies for both small and large anatomical structures. To maximise the utilities of U-net architecture, we apply three types of components, residual blocks, squeeze-and-excitation (SE) blocks, and dense blocks, to construct four variants of U-net, namely U-net variants. Among these variants, our experiments show that SE blocks can improve the segmentation accuracies of small labels. We adopt DeepLabv3plus architecture for 3D medical image segmentation by equipping SE blocks based on this discovery. The experimental results show that U-net with SE block achieves higher accuracy in parts of small anatomical structures. In contrast, DeepLabv3plus with SE block performs better on the average dice coefficient of small and large labels.

Telangiectatic soft tissue sarcoma and chronic expanding haematoma: a comparative review of MRI features

Soft tissue sarcomas containing a dominant component of haemorrhage are known to be aggressive tumours associated with a poor prognosis. Importantly, the clinical behaviour and imaging characteristics of extensively haemorrhagic soft tissue sarcomas (also termed telangiectatic soft tissue sarcomas) can resemble those of benign haematomas, particularly those that continue to expand over a prolonged period, so-called chronic expanding haematomas (CEH). The following review evaluates the current literature to identify the clinical, imaging and pathological characteristics of telangiectatic soft tissue sarcomas and to determine features that may help distinguish them from CEH. Ultimately, we suggest that lesions with sizeable regions of internal haemorrhage should be regarded with a high degree of suspicion for underlying malignancy and require referral to a tertiary sarcoma centre, where a carefully planned approach to biopsy and follow-up is needed to avoid errors in diagnosis.

Prevalence and characteristics of the aberrant anterior tibial artery: a single-center magnetic resonance imaging study and scoping review

Background

Planning surgical procedures of the lower leg benefits from considering the possibility of an aberrant anterior tibial artery (AATA), but previously published data on the frequency of this anatomic variant shows heterogeneity. We assessed the prevalence of AATA in a Latin American cohort using magnetic resonance imaging (MRI) and compared these with other studies reported in the literature.

Methods

We retrospectively included consecutive patients who had undergone multiplanar knee MRI at a radiology department in Lima, Peru. The MRI protocol included coronal T1 weighted, axial, sagittal and coronal proton density fat-saturated (PDFS) and sagittal T2 weighted images.

Two experienced radiologists assessed all images and were blinded to each other’s findings. The frequency of the AATA was compared to previous cohorts. A scoping review was undertaken to provide an overview of previously published data on the prevalence of ATAA.

Results

We analyzed 280 knee MRI examinations of 253 patients (median age 41 years (IQR 31–52), 53.8% male). The aberrant anterior tibial artery variant was present in 8 of 280 (2.9%) evaluated knees, resulting in a prevalence of 3.2% in our study population. The PDFS sequence in the axial or sagittal orientation was most effective to identify AATA. The frequency of AATA in the reviewed literature using different radiological modalities ranged from 0.4 to 6% (median 1%, IQR (0.5–2.3%).

Conclusions

The AATA is a frequent vascular variant that can be detected by MRI in the preparation of invasive interventions of the lower leg.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04801-9.

Relationship Between the Middle Genicular Artery and the Posterior Structures of the Knee: A Cadaveric Study

Background:

The middle genicular artery (MGA) is responsible for the blood supply to the cruciate ligaments and synovial tissue. Traumatic sports injuries and surgical procedures (open and arthroscopic) can cause vascular damage. Little attention has been devoted to establish safe parameters for the MGA.

Purpose:

To investigate the anatomy of the MGA and its relation to the posterior structures of the knees, mainly the posterior capsule and femoral condyles, and to establish safe parameters to avoid harming the MGA.

Study Design:

Descriptive laboratory study.

Methods:

Dissection of the MGA was performed in 16 fresh, unpaired adult human cadaveric knees with no macroscopic degenerative or traumatic changes and no previous surgeries. The specimens were meticulously evaluated with emphasis on preservation of the MGA. The distances from the MGA to the medial and lateral femoral condyles were measured. The Mann-Whitney test was used for statistical analysis.

Results:

In all specimens, the MGA emerged from the anterior aspect of the popliteal artery, distal to the superior genicular arteries, and had a short distal trajectory toward the posterior capsule where it entered proximal to the oblique popliteal ligament. The artery lay in the midportion between the condyles. The distance between the posterior aspect of the tibia and the point of entry of the MGA into the posterior joint capsule was 23.8 ± 7.3 mm (range, 14.72-35.68 mm). There was no correlation between an individual’s height and the distance of the entrance point of the MGA into the posterior joint capsule to the posterior superior corner of the tibia.

Conclusion:

The middle genicular artery lies in the midportion between the medial and lateral femoral condyles.

Clinical Relevance:

This knowledge is important for the preservation of the blood supply during posterior knee surgical procedures and to settle a secure distance between the posterior aspect of the tibia and the MGA input. This could decrease and prevent iatrogenic vascular injury risk to the MGA.

A diagnostic approach to popliteal fossa masses

There is a myriad of potential mass lesions that occur in the popliteal fossa, which present as palpable masses or are found incidentally on imaging. With a thorough knowledge and understanding of the appearances and locations of these different entities, one can narrow the differential diagnoses in the majority of cases. This will eliminate unnecessary additional investigations and enable a more rapid management. We present a review of frequently encountered and less common entities using an anatomical sieve, with the aim of providing a diagnostic approach to popliteal fossa masses.