Falx meningioma can be divided into anterior, middle, and posterior types, depending on their origin in the falx 1).
The anterior type extends from the floor of the anterior cranial fossa to the coronal suture, the middle type from the coronal suture to the lambdoid suture, and the posterior type extends from the lambdoid suture to the torcular Herophili.
Yasargil classified falcine meningiomas into outer and inner types. The former arises from the main body of the falx in the frontal (anterior or posterior), central parietal, or occipital regions, whereas inner falcine meningiomas arise in conjunction with the inferior sagittal sinus. 2).
Zuo et al classified FM into four types, according to tumor growth patterns on coronal MRI: Type I, hemispheroid-shaped tumors invaginating deeply into one hemisphere without shifting the falx (10 patients); Type II, olive-shaped tumors shifting the falx substantially to the contralateral side (six patients); Type IIIA, globular- or dumbbell-shaped tumors extending into both hemispheres, but to different extents (one patient); and Type IIIB, globular- or dumbbell-shaped tumors extending into both hemispheres to an approximately equal extent (three patients). An ipsilateral interhemispheric approach was performed for Type I tumors, and a contralateral transfalcine approach for Type II. Type IIIA tumor was approached from the side where the smaller tumour was located. Type IIIB tumors were approached from the non-dominant hemisphere 3).
Das et al. proposed a new classification schema:
Thirty-five patients with FM (mean age, 50.03 years; male/female ratio, 16:19) were classified into unilateral conventional (type I; n = 17), unilateral high (type II; n = 9), and bilateral FM (type III; n = 9) based on the coronal magnetic resonance imaging findings. We excluded the primary parasagittal meningiomas from our analysis.
Type II and III tumors were more common in males (unlike the overall cohort), presented more often with seizures, and were associated with less favorable postoperative outcomes. Preoperative motor weakness was almost exclusively seen with unilateral tumors (type I/II). Preexisting weakness (P = 0.02) was a strong predictor of the likelihood of postoperative motor power worsening, the major surgical complication in our series (n = 9; 25.7%). New-onset postoperative weakness (n = 2) recovered completely, whereas worsening of the preexisting weakness showed only a partial improvement (n = 6).
The proposed classification scheme characterizes FMs comprehensively. Bilaterality and parasagittal extensions in FMs affect their clinical presentation, increase surgical difficulty, and influence the surgical outcome adversely. Preexisting motor weakness portends a poor postoperative motor outcome 4).