Discussion:
Left Atrium (LA) is a low pressure , thin wall chamber located inferoposteriorly and highly vulnerable and liable to compression by dorsal mediastinal structure (1). The postero lateral approach of pulmonic veins are also susceptible to be compressed by same structures.
The subdivision proposed by D’Cruz et al (1 ) is as follows
  1. Proximity – a contiguous or adjacent structure without chamber deformation.
  2. Encroachment – distortion of normal cardio vascular architecture without haemodynamic effect.
  3. Compression –where impression is responsible for development of haemodynamic instability and symptoms(2).
The above mentioned impressions is clearly seen on TTE as deformed and smaller LA which leads to low output state and causes symptoms like dyspnoea, reduced exercise tolerance , easy fatigue ability and even hemodynamic instability. Depending on the severity or degree of compression , LA pressure may rises to a level leading to pulmonary oedema mimicking heart failure or cardiac temponade (2).
TTE can easily visualise distorted shape of LA by conventional and unconventional views except (i) extreme obesity (ii)poor echo window (iii) previous cardio thoracic surgery (iv) patient on mechanical ventilation etc.
With the aid of color Doppler ,we can pick up turbulent flow due to compressed LA and pulmonic veins. Similarly by additional use of agitated saline contrast echo and ingestion of aerated drinks orally , the vascular and non vascular causes of LA impression can be ruled out (3).
However , Right heart catheterisation , Computed tomography , Cardiac MRI techniques may be finally conclusive , to aid into further management .
As reported before on the basis of its origin , the compression can be classified (4-7):
A: Gastrointestinal (GI) tract structures
B: Mediastinal structure
C: Aorta / Intrapericardial structure
D:Pulmonary structure
But the compression by dorsum spine is not reported in the literature . We , hereby report one such case of LA compression/ impression with dorsal spine , although we have seen two of them.