Singapore Med J 2007; 48(12) : 1156
C a s e R e p o r t
During routine dissection in the department
of anatomy, the following anatomical
variations of the phrenic nerve were
observed on the right side of the neck of
a 30-year-old male cadaver. The phrenic
nerve, in its early course close to its
origin, gave a communicating branch
to the C5 root of the brachial plexus. At
the level of the root of neck just before
entering the thorax, the phrenic nerve
was located anterior to the subclavian vein.
This unique case of phrenic nerve variation
gains tremendous importance in the context
of subclavian vein cannulation, implanted
venous access portals, and supraclavicular
nerve block for regional anaesthesia.
Keywords: anatomical variations, brachial
plexus, neck anatomy, phrenic nerve
Singapore Med J 2007; 48(12):1156–1157
Variations of the phrenic nerve have been observed
and reported in the past.(1-3) Right subclavian vein
cannulation is a commonly-performed procedure for
vascular access for haemodialysis, and the phrenic
nerve palsy manifesting as hemidiaphragmatic paralysis
is an important complication associated with it.(4-8)
Right phrenic nerve paralysis is an acknowledged
immediate and late complication of implanted
venous access portals.(9) Bigeleisen reported a case
of simultaneous diaphragmatic and brachial plexus
stimulation, followed by a successful nerve block,
and demonstrated the necessity of a thorough
knowledge of anatomical variations and standard
anatomy, for the safe and efficient practice for
The following important variations were observed
only on the right side during routine dissection in a
30-year-old male cadaver. The phrenic nerve, in its
early course close to its origin, gave a communicating
branch to the C5 root of the brachial plexus (Fig. 1).
Prakash, Prabhu L V, Madhyastha S, Singh G
Centre for Basic
Prakash, MBBS, MD
Prabhu LV, MBBS,
Professor and Head
Madhyastha S, MSc,
Institute of Medical
Professor and Director
Vyhedi Institute of
Medical Sciences &
82 EPIP Area,
Tel: (91) 9480 229 670
Fax: (91) 8028 416 199
The phrenic nerve at the level of the root of the neck,
just before entering the thorax, was located in front
of the subclavian vein (Fig. 1). It is usually located
posteriorly, in between subclavian vein and artery.
This variation of phrenic nerve makes it highly
vulnerable to injury during subclavian catheterisation
for vascular access.
The accessory phrenic nerve proceeds caudally and
joins distally with phrenic nerve, and is present in up
to 75% of cadavers.(10) On the contrary, in this particular
case, the variation is not an accessory phrenic nerve;
as the communicating branch from the phrenic nerve
to the C5 root of the brachial plexus proceeded
distally and laterally in caudal direction and joined
the C5 root of the brachial plexus. Hollinshead
described that the entire phrenic nerve, in ten out of
138 (7.25%) sides of cadavers studied, passed anterior
to subclavian vein as it leaves the neck,(1) whereas in
the present case, this particular variation of phrenic
nerve was accompanied further by a communicating
branch to the C5 root of the brachial plexus.
A variation of the phrenic nerve:
case report and review
Fig. 1 Photograph shows the variations of the phrenic nerve.
AC: ansa cervicalis; CB: communicating branch to brachial
plexus; C5: C5 root of brachial plexus; PN: phrenic nerve;
IJV: Internal jugular vein; SCV: subclavian vein
Singapore Med J 2007; 48(12) : 1157
2 Anson BJ, McVay CB. Surgical Anatomy. 5th ed. Philadelphia:
WB Saunders, 1971.
Human Anatomical Variation. Baltimore: Urban and Schwarzenburg,
4 Islek I, Akpolat T, Danaci M. Phrenic nerve palsy caused by
subclavian vein catheterization. Nephrol Dial Transplant, 1998;
5 Porzionato A, Montisci M, Manani G. Brachial plexus injury following
subclavian vein catheterization: a case report. J Clin Anesth 2003;
6 Akata T, Noda Y, Nagata T, Noda E, Kandabashi T. Hemidiaphragmatic
paralysis following subclavian vein catheterization. Acta Anaesthesiol
Scand 1997; 41:1223-5.
7 D’Netto MA, Bender J, Brown RT, Herson VC. Unilateral
diaphragmatic palsy in association with a subclavian vein
thrombus in a very-low-birth weight infant. Am J Perinatol 2001;
8 Aggarwal S, Hari P, Bagga A, Mehta SN. Phrenic nerve palsy:
a rare complication of indwelling subclavian vein catheter. Pediatr
Nephrol 2000; 14:203-4.
9 Reeves JE Jr, Anderson WF. Permanent paralysis of the right
phrenic nerve. Ann Intern Med 2002; 137:551-2.
10 Bigeleisen PE. Anatomical variations of the phrenic nerve and its
clinical implication for supraclavicular block. Br J Anaesth 2003;
11 Sanes DH, Reh TA, Harris WA. Development of the Nervous System.
London: Academic Press, 2000.
Bigeleisen reported that more distal blocks,
such as a low interscalene or supraclavicular block,
may also give rise to a partial phrenic nerve block,
even if the phrenic nerve anatomy is standard.(10)
In the context of the present case, this will lead
to complete phrenic nerve block manifesting as
right diaphragmatic paralysis. The guidance of the
developing axons is regulated by expression of
chemoattractants and chemorepulsants, in a highly-
coordinated? site? specific? fashion.? Any? alterations? in?
signalling between mesenchymal cells and neuronal
probably in the present case, resulted in phrenic
nerve communication with the C5 root of the brachial
plexus, along with subclavian vein located posterior
to the phrenic nerve. Once formed, any developmental
differences would persist postnatally.(11)
1 Hollinshead WH. Anatomy for Surgeons. The Head and Neck. 3rd ed.
New York: Harper and Row Publishers, 1982.