European Radiology: radioprognostic factors for synovial sarcoma of the extremities

Synovial sarcoma (SS) is an undifferentiated tumour that accounts for about 4-5%
of soft tissue sarcomas.
The extremities are the most common site (about 65%), but SS can also occur in the chest, abdomen, or head and neck, mainly in adolescents and young adults, with the pediatric type accounting for 10%, and older patients are rarely affected
.
Clinically, these lesions can develop
slowly over months or years.

Imaging is often used as an important tool in diagnosing, staging, and planning treatment of SS.

However, the radiographic features of SS are nonspecific
.
Computed tomography (CT) scans show low-density masses and calcifications
are visible in 30% of cases.
Magnetic resonance imaging (MRI) often presents as heterogeneous masses: on T2-weighted imaging (WI), SS presents a "triad" of low, medium, and high signal regions
.
Another radiographic finding is "pseudocystic" SS, which may be mistaken for cystic lesions
on T2WI.
Because clinical and radiographic features can be misleading, these tumors are often mistaken for benign tumors without prompt surgical treatment
.
A current knowledge gap is determining whether imaging phenotypes can be used to predict outcomes and outcomes
.
Radiographic variables should also be reproducible as clinically relevant prognostic factors (PFs).

Prognostic factors listed in the literature include age, grade, size, location, imaging features, and molecular variation
.
Metastasis of SS may develop very late (> 5 or even > 10 years) and adequate follow-up is essential
.
However, these clinical, pathological, and imaging PFs have not been independently studied
in large populations of patients with long-term follow-up.

Recently, a study published in the journal European Radiology explored whether the imaging phenotype of SS can provide added value for the currently known PF-age and pathological grade, predict overall survival (OS) and survival without local recurrence (LRFS), and provide imaging support
for early clinical diagnosis and non-invasive pathological classification.


This retrospective, multicenter study included consecutive children and adults with synovial sarcoma of the extremities between December 2002 and August 2020
.
The inclusion criteria were: (i) follow-up over five years; (ii) MRI prior to
treatment.
One subset of analyses included MRI and CT scans
.
Clinical, pathological, and imaging variables
were collected for all patients.
The primary endpoint was to evaluate the relationship of these variables to OS using univariate and multivariate Cox regression
.

Of the 428 patients screened, a total of 98 (mean age: 37.
1±15.
2 years) were included (MRI: n = 98/98, CT scan: n = 34/98; 35%)
.
The median OS was 75.
25 months (IQR = 55.
50-109.
12) in 36 patients (n = 36/98; 37%) died
during follow-up.
The recurrence rate was 12.
2% (n = 12/98).

SS lesions are mostly grade 2 (57/98; 58%)
.
On MRI, the average long-axis diameter of SS is 67.
5 ± 38.
3 mm
.
On CT scans, calcifications were present in 44% (15/34) of lesions.

Grade (hazard ratio [HR] = 2.
71; 95% CI = 1.
30-5.
66; p=0.
008), lesion size assessed on MRI (HR=1.
02; 95%CI=1.
01-1.
03; p<0.
001), and calcification on CT scan (HR=0.
10; 95%CI=0.
02-0.
50; p=0.
005) were independent PFs of OS
。

A 40-year-old patient with SS grade 3 FNCLCC shows a "triad" (A) on T2WI and no calcifications on CT scan (B).

This large lesion is manifested on contrast-enhanced MRI as necrosis and bleeding (C, D), pathology (E).

There is nodular strengthening around the lesion (D).

The patient died about 2 years after diagnosis

This study shows that the radiographic features of SS play a key
role in assessing the prognosis of patients and formulating treatment regimens.
In addition to age and histologic grade, MRI's assessment of lesion size is a major independent factor
.
The value of CT scans should also be emphasized in SS of the extremities, as calcified lesions often indicate a better prognosis
.

Original source:

Mickael Tordjman,Charles Honoré,Amandine Crombé,et al.
Prognostic factors of the synovial sarcoma of the extremities: imaging does matter.
DOI:10.
1007/s00330-022-09049-y